home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
C++ Games Programming
/
CPPGAMES.ISO
/
fgl
/
fglight
/
manuals.arj
/
USER05.DOC
< prev
next >
Wrap
Text File
|
1995-02-06
|
75KB
|
1,606 lines
Chapter 5
The Use of Color
68 Fastgraph User's Guide
Overview
The use of color is an important part of any text or graphics
application. This chapter explains color as it applies to text and graphics
modes. It also describes palettes and video DAC registers for the graphics
video modes that offer this functionality. Finally, an explanation of
Fastgraph's virtual colors is provided.
Text Modes
The term color is not really correct in text modes because each character
cell has an associated attribute that controls the character's appearance in
that cell. The meaning of the attribute differs for color and monochrome text
modes.
Color Text Modes
In color text modes (modes 0, 1, 2, and 3), the attribute determines a
character's foreground color (the color of the character itself), its
background color (the color of that part of the character cell not covered by
the character), and whether or not it blinks. Sixteen foreground colors
(numbered 0 to 15) are available, but only eight background colors (numbered 0
to 7) are available. The colors assigned to these values are listed in the
following table.
number color number color
0 black 8 dark gray
1 blue 9 light blue
2 green 10 light green
3 cyan 11 light cyan
4 red 12 light red
5 magenta 13 light magenta
6 brown 14 yellow
7 gray 15 white
At first it may seem the numbers have been arbitrarily assigned to the colors.
Upon further inspection, however, it becomes apparent this is not the case.
Each color number is a four bit quantity of the form IRGB, with I representing
the intensity, R the red component, G the green component, and B the blue
component. If the corresponding bit is 1, it means the intensity or color
component is set. For example, normal red would be represented by the IRGB bit
pattern 0100, which is 4 decimal, the color number for red.
The fg_setattr routine defines the current text attribute. Once
fg_setattr is called, Fastgraph displays all subsequent text using that
attribute. The first argument of fg_setattr defines the foreground color,
which must be an integer between 0 and 15. Its second argument defines the
background color, which must be between 0 and 7. Its third argument determines
if the foreground color blinks (1 means it blinks, 0 means it does not). For
example, the statement
fg_setattr(14,1,0);
Chapter 5: The Use of Color 69
specifies subsequent text will be displayed with a yellow foreground (14) on a
blue background (1) and will not blink (0).
Another Fastgraph routine, fg_setcolor, also can define text attributes.
The fg_setcolor routine packs the three values passed to fg_setattr into a
single argument, as shown here:
bits attribute
0-3 foreground color
4-6 background color
7 blinking
For example, calling fg_setcolor with an argument of 30 (1E hex) is equivalent
to calling fg_setattr with arguments of 14, 1, and 0.
The Fastgraph routine fg_getcolor returns the current text attribute, as
defined in the most recent call to fg_setattr or fg_setcolor. The fg_getcolor
routine has no arguments and returns the attribute as its function value. The
returned value is encoded using the same scheme for passing a text attribute
to fg_setcolor.
Monochrome Text Mode
In the monochrome text mode (mode 7), colors are obviously not available.
The attribute instead determines whether a character is invisible, normal,
bold, reversed, or certain combinations of these. The following table shows
the values assigned to the available display characteristics.
foreground background characteristic
0 0 invisible
0 7 reversed
1 0 underlined
7 0 normal
9 0 underlined bold
15 0 bold
Additionally, you can turn blinking on or off for each of these combinations.
Any combination of foreground and background values not listed in the above
table produces a normal display characteristic.
As in the color modes, the Fastgraph routines fg_setattr and fg_setcolor
define the current text attribute. For example, the statement
fg_setattr(0,7,1);
specifies subsequent text will be displayed in reverse video (0,7) and will
blink (1). The same attribute could be defined by calling fg_setcolor with an
argument of 240 (F0 hex). The fg_getcolor routine is also available and works
as it does in the color text modes.
70 Fastgraph User's Guide
Graphics Modes
In graphics modes, each pixel has an associated color value that
determines the color in which the pixel is displayed. The number of available
colors depends on the video mode and can be obtained through the fg_colors
function. Some graphics modes also have palette registers or video DAC
registers to provide additional color capabilities, such as choosing a set of
colors from a larger palette of colors. The example programs presented in this
section show the use of color in specific graphics video modes.
The following subsections will discuss the use of color in each graphics
video mode. In these discussions, there will be several references to a group
of colors called the standard color set. This is a set of 16 colors common to
many of the graphics video modes (and to the color text modes). The colors in
the standard color set are listed in the following table.
number color number color
0 black 8 dark gray
1 blue 9 light blue
2 green 10 light green
3 cyan 11 light cyan
4 red 12 light red
5 magenta 13 light magenta
6 brown 14 yellow
7 gray 15 white
At this point we must understand the difference between the terms color
number and color value. Color number refers to the number that defines a color
in the standard color set (for example, green is color number 2). Color value
refers to the actual value of a pixel in video memory, which ultimately
determines the color in which that pixel is displayed. The color value is
sometimes just called the color.
In each graphics mode, video memory is cleared when the fg_setmode
routine is called. This means all pixels are initially set to color value 0,
which by default is black. For this reason, color value 0 is often called the
background color in graphics video modes.
Fastgraph's fg_setcolor routine defines the color in which subsequent
graphics operations are performed. This color is called the current color.
Depending on the video mode, the current color can reference a color value (in
CGA and Hercules graphics modes), a palette register (in Tandy, EGA, and VGA
graphics modes), or a video DAC register (in 256-color modes). The fg_setcolor
routine takes a single integer argument that specifies the color. When
fg_setmode is called, it sets the current color to 0. The Fastgraph routine
fg_getcolor returns the current color, as defined in the most recent call to
fg_setcolor. The fg_getcolor routine has no arguments and returns the current
color as its function value.
CGA Color Modes
The CGA color modes (modes 4 and 5) have six sets of available colors,
called palettes, numbered 0 to 5. Each palette consists of four colors,
Chapter 5: The Use of Color 71
numbered 0 to 3. In each palette, the background color (color value 0) can be
selected from the standard color set, but the other 3 colors are fixed. The
following table shows the fixed colors assigned to each palette.
palette 0 palette 1 palette 2
color 1 light green light cyan light cyan
color 2 light red light magenta light red
color 3 yellow white white
palette 3 palette 4 palette 5
color 1 green cyan cyan
color 2 red magenta red
color 3 brown gray gray
Palette 1, with a black background, is the default palette when you select
mode 4. Palette 2, with a black background, is the default palette when you
select mode 5.
The CGA color modes have a border area called the overscan between the
addressable pixel space and the physical edges of the screen. The overscan
area is always displayed in the background color, regardless of which CGA
palette is used.
In CGA color modes, fg_setcolor defines the current color by referencing
one of the four color values. The fg_palette routine selects one of the six
palettes and defines the background color for that palette. The first argument
of fg_palette is an integer between 0 and 5 that specifies the palette number.
The second argument is an integer between 0 and 15 that defines the background
color, using the color numbers in the standard color set.
Example 5-1 demonstrates the use of fg_palette and fg_setcolor in mode 4.
After establishing the video mode, the program selects palette 0 and makes the
background color blue (color number 1). It then makes color 3 in palette 0
(yellow) the current color and displays the word "Hello". Finally, it restores
the original video mode and screen attributes before returning to DOS.
Example 5-1.
#include <fastgraf.h>
void main(void);
void main()
{
int mode;
fg_initpm();
mode = fg_getmode();
fg_setmode(4);
fg_palette(0,1);
fg_setcolor(3);
fg_text("Hello",5);
72 Fastgraph User's Guide
fg_waitkey();
fg_setmode(mode);
fg_reset();
}
CGA Two-Color Mode
The CGA two-color mode (mode 6) has a fixed background color (color value
0) and a user-definable foreground color (color value 1). The background color
is always black. The foreground color is white by default but can be changed
to any of the colors in the standard color set. We should mention that
changing the foreground color works on true CGA adapters, but there are very
few EGA, VGA, and SVGA adapters that correctly implement changing the
foreground color in their mode 6 emulation.
In mode 6, fg_setcolor defines the current color by referencing one of
the two color values. The fg_palette routine defines the actual foreground
color (that is, the color of pixels whose color value is 1). For consistency
with other graphics modes, fg_palette has two arguments, but the first one is
not used. The second argument is an integer between 0 and 15 that defines the
foreground color, using the color numbers in the standard color set.
Example 5-2 demonstrates the use of fg_palette and fg_setcolor in mode 6.
After establishing the video mode, the program makes the foreground color
yellow (color number 14). It then makes color 1 the current color and displays
the word "Hello". Finally, it restores the original video mode and screen
attributes before returning to DOS.
Example 5-2.
#include <fastgraf.h>
void main(void);
void main()
{
int mode;
fg_initpm();
mode = fg_getmode();
fg_setmode(6);
fg_palette(0,14);
fg_setcolor(1);
fg_text("Hello",5);
fg_waitkey();
fg_setmode(mode);
fg_reset();
}
Chapter 5: The Use of Color 73
Tandy and PCjr Modes
The supported Tandy 1000 or PCjr graphics mode (mode 9) has 16 color
values, numbered 0 to 15. Each color value references one of 16 user-definable
palette registers, often simply called palettes, also numbered 0 to 15. The
values assigned to the palette registers determine the colors in which pixels
are displayed. For example, if you assign palette register 2 the value for
red, then pixels whose color value is 2 will be red.
Each palette can assume one of the 16 colors in the standard color set.
By default, the values assigned to the 16 palettes correspond to the
identically numbered colors in the standard color set. In other words, palette
0 is assigned the value for black, palette 1 is assigned the value for blue,
and so forth.
In mode 9, fg_setcolor defines the current color by referencing one of
the 16 palette registers. The fg_palette routine defines the actual color
assigned to a specific palette register. The first argument of fg_palette is
an integer between 0 and 15 that specifies the palette number. The second
argument is an integer between 0 and 15 that defines the palette value (the
color assigned to the palette), using the IRGB color numbers in the standard
color set.
You also can use the Fastgraph routine fg_setrgb to define the color
assigned to a specific palette register. While fg_palette does this using a
color number from the standard color set, fg_setrgb defines a palette register
using red, green, and blue color components plus an intensity component. The
first argument of fg_setrgb is an integer between 0 and 15 that specifies the
palette register number. The remaining three arguments are each integer values
between -1 and 1 that respectively specify the red, green, and blue color
components for that palette register. The meanings of the color components
are:
-1 = color bit and intensity bit are set
0 = color bit is reset
1 = color bit is set
Since there is only one intensity bit in mode 9 color values, specifying -1
for any of the RGB color components produces an intense color. For example,
the color light cyan is color number 11 in the standard color set, and it is
produced by combining green and blue and setting the intensity bit. This means
any of these four statements
fg_palette(1,11);
fg_setrgb(1,0,-1,1);
fg_setrgb(1,0,1,-1);
fg_setrgb(1,0,-1,-1);
could be used to define palette register 1 as light cyan in mode 9.
Example 5-3 demonstrates the use of fg_palette and fg_setcolor in mode 9.
After establishing the video mode, the program defines palette 0 to be blue
(1) and palette 1 to be yellow (14). Note that defining palette 0 changes the
74 Fastgraph User's Guide
background color. It then makes color 1 the current color and displays the
word "Hello". After waiting for a keystroke, the program changes the color of
"Hello" by changing palette 1 to white (15). Finally, it restores the original
video mode and screen attributes before returning to DOS.
Example 5-3.
#include <fastgraf.h>
void main(void);
void main()
{
int mode;
fg_initpm();
mode = fg_getmode();
fg_setmode(9);
fg_palette(0,1);
fg_palette(1,14);
fg_setcolor(1);
fg_text("Hello",5);
fg_waitkey();
fg_palette(1,15);
fg_waitkey();
fg_setmode(mode);
fg_reset();
}
Hercules Mode
The Hercules graphics mode (mode 11) has a fixed background color (color
value 0) and a fixed foreground color (color value 1). The background color is
always black, and the foreground color is dependent on the monochrome display
being used (typically it is green, amber, or white).
The fg_setcolor routine defines the current color value by referencing
one of the two color values. The fg_palette routine has no effect in mode 11.
Example 5-4 demonstrates the use of fg_setcolor in mode 11. After
establishing the video mode, the program makes color 1 the current color and
displays the word "Hello". It then restores the original video mode and screen
attributes before returning to DOS.
Example 5-4.
#include <fastgraf.h>
void main(void);
void main()
{
Chapter 5: The Use of Color 75
int mode;
fg_initpm();
mode = fg_getmode();
fg_setmode(11);
fg_setcolor(1);
fg_text("Hello",5);
fg_waitkey();
fg_setmode(mode);
fg_reset();
}
Hercules Low-Resolution Mode
The Hercules low-resolution graphics mode (mode 12) has four color
values, numbered 0 to 3. The background color is always black, colors 1 and 2
are normal intensity, and color 3 is full intensity. Colors 1 and 2 both
produce normal intensity colors, but they do so with different pixel
patterns -- color 1 turns on the odd-numbered physical pixels, while color 2
turns on the even-numbered physical pixels. The appearance of colors 1 to 3 is
dependent on the monochrome display being used (typically it is green, amber,
or white).
The fg_setcolor routine defines the current color value by referencing
one of the four color values. The fg_palette routine has no effect in mode 12.
Example 5-5 demonstrates the use of fg_setcolor in mode 12. After
establishing the video mode, the program makes color 3 the current color and
displays the word "Hello". It then restores the original video mode and screen
attributes before returning to DOS.
Example 5-5.
#include <fastgraf.h>
void main(void);
void main()
{
int mode;
fg_initpm();
mode = fg_getmode();
fg_setmode(12);
fg_setcolor(3);
fg_text("Hello",5);
fg_waitkey();
fg_setmode(mode);
fg_reset();
}
76 Fastgraph User's Guide
EGA 200-Line Modes
The 200-line EGA graphics modes (modes 13 and 14) have 16 color values,
numbered 0 to 15. Each color value references one of 16 user-definable palette
registers, often simply called palettes, also numbered 0 to 15. The values
assigned to the palette registers determine the colors in which pixels are
displayed. For example, if you assign palette register 2 the value for red,
then pixels whose color value is 2 will be red.
Each palette can assume one of the 16 colors in the standard color set.
By default, the values assigned to the 16 palettes correspond to the
identically numbered colors in the standard color set. In other words, palette
0 is assigned the value for black, palette 1 is assigned the value for blue,
and so forth.
In modes 13 and 14, fg_setcolor defines the current color by referencing
one of 16 available palette registers. The fg_palette routine defines the
actual color assigned to a specific palette register. The first argument of
fg_palette is an integer between 0 and 15 that specifies the palette number.
The second argument is an integer that defines the palette value (the color
assigned to the palette). Although the actual colors are taken from the
standard color set, the binary structure of a palette value is different from
the IRGB format used in the standard color set. In modes 13 and 14, the binary
structure of a palette value is IxRGB; bit 3 is ignored. The mode 13 and mode
14 palette values that correspond to the standard color set are thus:
value color value color
0 black 16 dark gray
1 blue 17 light blue
2 green 18 light green
3 cyan 19 light cyan
4 red 20 light red
5 magenta 21 light magenta
6 brown 22 yellow
7 gray 23 white
You also can use the Fastgraph routine fg_setrgb to define the color
assigned to a specific palette register. While fg_palette does this using a
color number from the standard color set, fg_setrgb defines a palette register
using red, green, and blue color components, plus an intensity component. The
first argument of fg_setrgb is an integer between 0 and 15 that specifies the
palette register number. The remaining three arguments are each integer values
between -1 and 1 that respectively specify the red, green, and blue color
components for that palette register. The meanings of the color components
are:
-1 = color bit and intensity bit are set
0 = color bit is reset
1 = color bit is set
Since there is only one intensity bit in mode 13 and 14 color values,
specifying -1 for any of the RGB color components produces an intense color.
For example, light cyan is represented by the color value 19, and it is
Chapter 5: The Use of Color 77
produced by combining green and blue and setting the intensity bit. This means
any of these four statements
fg_palette(1,19);
fg_setrgb(1,0,-1,1);
fg_setrgb(1,0,1,-1);
fg_setrgb(1,0,-1,-1);
could be used to define palette register 1 as light cyan in modes 13 and 14.
The Fastgraph routine fg_setcolor defines the color value (that is, the
palette number) in which subsequent graphics operations are performed. The
fg_setcolor routine takes a single integer argument that specifies this color.
When fg_setmode is called, it sets the color value to 0. The Fastgraph routine
fg_getcolor returns the current color value, as defined in the most recent
call to fg_setcolor. The fg_getcolor routine has no arguments and returns the
current color as the function value.
Example 5-6 demonstrates the use of fg_palette and fg_setcolor in mode
13. After establishing the video mode, the program defines palette 0 to be
blue (1) and palette 1 to be yellow (22). Note that defining palette 0 changes
the background color. It then makes color 1 the current color and displays the
word "Hello". After waiting for a keystroke, the program changes the color of
"Hello" by changing palette 1 to white (23). Finally, it restores the original
video mode and screen attributes before returning to DOS.
Example 5-6.
#include <fastgraf.h>
void main(void);
void main()
{
int mode;
fg_initpm();
mode = fg_getmode();
fg_setmode(13);
fg_palette(0,1);
fg_palette(1,22);
fg_setcolor(1);
fg_text("Hello",5);
fg_waitkey();
fg_palette(1,23);
fg_waitkey();
fg_setmode(mode);
fg_reset();
}
78 Fastgraph User's Guide
EGA Monochrome Mode
The EGA monochrome graphics mode (mode 15) assigns display attributes to
its four color values, numbered 0 to 3. Each color value references one of
four user-definable palette registers, often simply called palettes, numbered
0, 1, 4, and 5. This strange numbering results from the disabling of two of
the four video memory bit planes in mode 15. The values assigned to the
palette registers determine the pixel display attribute. For example, if you
assign palette register 1 the value for bold, then pixels whose value is 1
will be bold.
In mode 15, fg_setcolor defines the current color (actually, a display
attribute) by referencing one of the four palette registers. The fg_palette
routine defines the actual display attribute assigned to a specific palette
register. The first argument of fg_palette is an integer that specifies the
palette number. The second argument is an integer that defines the palette
value (the display attribute assigned to the palette). For each palette
register, the following table shows the default palette value and its
associated display attribute.
palette palette display
number value attribute
0 0 invisible
1 8 normal
4 24 bold
5 24 bold
Example 5-7 demonstrates the use of fg_palette and fg_setcolor in mode
15. After establishing the video mode, the program makes color 4 (actually,
palette 4, which is bold by default) the current color and displays the word
"Hello". After waiting for a keystroke, the program changes the display
attribute of "Hello" by changing palette 4 to normal intensity (palette value
8). Finally, it restores the original video mode and screen attributes before
returning to DOS.
Example 5-7.
#include <fastgraf.h>
void main(void);
void main()
{
int mode;
fg_initpm();
mode = fg_getmode();
fg_setmode(15);
fg_setcolor(4);
fg_text("Hello",5);
fg_waitkey();
fg_palette(4,8);
fg_waitkey();
Chapter 5: The Use of Color 79
fg_setmode(mode);
fg_reset();
}
EGA Enhanced Mode
The EGA enhanced graphics mode (mode 16) has 16 color values, numbered 0
to 15. Each color value references one of 16 user-definable palette registers,
often simply called palettes, also numbered 0 to 15. The values assigned to
the palette registers determine the colors in which pixels are displayed. For
example, if you assign palette register 2 the value for red, then pixels whose
color value is 2 will be red.
Each palette can assume one of 64 available colors. By default, the
values assigned to the 16 palettes correspond to the identically numbered
colors in the standard color set. In other words, palette 0 is assigned the
value for black, palette 1 is assigned the value for blue, and so forth. There
are a few EGA-compatible adapters that do not properly assign the default
colors to the 16 palette registers, so it is a good practice to do this
explicitly in mode 16.
In mode 16, fg_setcolor defines the current color value by referencing
one of the 16 palette registers. The fg_palette routine defines the actual
color assigned to a specific palette register. The first argument of
fg_palette is an integer between 0 and 15 that specifies the palette number.
The second argument is an integer that defines the palette value (the color
assigned to the palette). The binary structure of a palette value is different
from the IRGB format used in the standard color set. In mode 16, the binary
structure of a palette value is a 6-bit quantity of the form rgbRGB, where the
lower case letters represent the low intensity (1/3 intensity) color
components, and the upper case letters represent the normal intensity (2/3
intensity) color components. The mode 16 palette values that correspond to the
standard color set are:
value color value color
0 black 56 dark gray
1 blue 57 light blue
2 green 58 light green
3 cyan 59 light cyan
4 red 60 light red
5 magenta 61 light magenta
20 brown 62 yellow
7 gray 63 white
The normal intensity components in mode 16 produce the same normal
intensity colors as in other 16-color graphics modes. Similarly, combining the
low and normal intensities in mode 16 produces the high intensity colors of
the other modes. The only exception to this is for the default brown, formed
from the bit pattern 010100 (20 decimal). This value produces a more true
brown than the value 6 decimal, which is really an olive green.
80 Fastgraph User's Guide
The palette values used in mode 16 are 6-bit quantities, which means
there are 64 different colors available in mode 16. This group of 64 colors
consists of the 16 colors in the standard color set plus 48 additional colors
that are not available in any other EGA modes. However, because the EGA
palette registers hold 4-bit quantities, only 16 of these colors can be
displayed at the same time. In other words, the EGA enhanced mode provides the
capability of displaying 16 simultaneous colors from a group of 64.
You also can use the Fastgraph routine fg_setrgb to define the color
assigned to a specific palette register. While fg_palette does this using a
value between 0 and 63, fg_setrgb defines a palette register using red, green,
and blue color components. The first argument of fg_setrgb is an integer
between 0 and 15 that specifies the palette register number. The remaining
three arguments are each integer values between 0 and 3 that respectively
specify the intensities in thirds of the red, green, and blue color components
for that palette register. For example, the color cyan is represented by the
value 3 in the above table, and it is produced by combining normal intensity
(2/3 intensity) green and blue. This means either of the statements
fg_palette(1,3);
fg_setrgb(1,0,2,2);
could be used to define palette register 1 as cyan.
Example 5-8 demonstrates the use of fg_palette and fg_setcolor in mode
16. It uses the Fastgraph routine fg_rect (discussed in the next chapter) to
draw rectangles of a specified size. After establishing the video mode, the
program uses a for loop to draw 16 equal-size rectangles, one in each of the
16 color values. In the same loop, the program uses fg_palette to change each
palette to black. The while loop that follows performs four iterations. The
first iteration changes palette 0 to 0, palette 1 to 1, and so forth. Hence,
the 16 rectangles appear in the palette values 0 to 15. The rectangles remain
in these colors until is key is pressed to begin the next iteration. The
second iteration changes palette 0 to 16, palette 1 to 17, and so forth. This
makes the 16 rectangles appear in the palette values 16 to 31. Iterations
three and four are similar, so the overall effect of the program is to display
all 64 colors, 16 at a time. Finally, the program restores the original video
mode and screen attributes before returning to DOS.
Example 5-8.
#include <fastgraf.h>
void main(void);
#define COLORS 16
#define WIDTH 40
void main()
{
int base;
int color;
int minx, maxx;
int mode;
Chapter 5: The Use of Color 81
fg_initpm();
mode = fg_getmode();
fg_setmode(16);
base = 0;
minx = 0;
maxx = WIDTH - 1;
for (color = 0; color < COLORS; color++) {
fg_palette(color,0);
fg_setcolor(color);
fg_rect(minx,maxx,0,349);
minx = maxx + 1;
maxx = maxx + WIDTH;
}
while (base < COLORS*4) {
for (color = 0; color < COLORS; color++)
fg_palette(color,base+color);
base += COLORS;
fg_waitkey();
}
fg_setmode(mode);
fg_reset();
}
VGA and MCGA Two-Color Mode
The VGA and MCGA two-color mode (mode 17) has a background color (color
value 0) and a foreground color (color value 1). Each color value references
one of two user-definable palette registers, often simply called palettes,
also numbered 0 and 1. Each palette register in turn references one of 16
user-definable 18-bit video DAC registers, numbered 0 to 15. The values
assigned to the palette registers and video DAC registers determine the colors
in which pixels are displayed. For example, if palette register 1 contains the
value 3, and video DAC register 3 contains the color value for red, then
pixels whose color value is 1 (that is, the foreground pixels) will be red.
By default, palette register 0 references video DAC register 0, and
palette register 1 references video DAC register 1. In addition, video DAC
register 0 initially contains the color value for black, while the other 15
video DAC registers (1 through 15) contain the color value for white. This
means background pixels (color value 0) are black by default, while foreground
pixels (color value 1) are white.
The 18-bit video DAC values consist of three 6-bit red, green, and blue
color components. Hence, each color component is an integer between 0 and 63;
increasing values produce more intense colors. The default color components
for DAC register 0 are red=0, blue=0, and green=0, which produces black. The
default values for the other DAC registers are red=63, blue=63, and green=63,
which produces white. Because the video DAC registers are 18 bits long, each
DAC can specify one of 262,144 (2**18) colors. However, because the palette
registers hold 1-bit quantities, only two of these colors can be displayed at
82 Fastgraph User's Guide
the same time. In other words, mode 17 provides the capability of displaying
two simultaneous colors from a group of 262,144.
In mode 17, fg_setcolor defines the current color by referencing one of
the two palette registers. The fg_palette routine defines the value of a
palette register by referencing one of the 16 video DAC registers. That is,
fg_palette specifies the video DAC register that a palette register
references. The first argument of fg_palette is either 0 or 1 and specifies
the palette number. The second argument is an integer between 0 and 15 that
specifies the video DAC register for that palette.
The Fastgraph routine fg_setrgb defines the value of a video DAC register
in mode 17. The first argument of fg_setrgb is an integer between 0 and 15
that specifies the DAC register number. The remaining three arguments are each
integer values between 0 and 63 that respectively specify the red, green, and
blue color components for that DAC register.
Example 5-9 demonstrates the use of fg_palette, fg_setrgb, and
fg_setcolor in mode 17. After establishing the video mode, the program defines
DAC register 0 to be blue (red=0, green=0, blue=42) and DAC register 1 to be
yellow (red=63, green=63, blue=21). Note that defining DAC register 0 changes
the background color because palette 0 references DAC register 0. The program
then makes color 1 the current color (palette 1 still references DAC register
1) and displays the word "Hello" in yellow. After waiting for a keystroke, the
program changes the color of "Hello" by making palette 1 reference DAC
register 15 (which still contains its default value, white). Finally, it
restores the original video mode and screen attributes before returning to
DOS.
Example 5-9.
#include <fastgraf.h>
void main(void);
void main()
{
int mode;
fg_initpm();
mode = fg_getmode();
fg_setmode(17);
fg_setrgb(0,0,0,42);
fg_setrgb(1,63,63,21);
fg_setcolor(1);
fg_text("Hello",5);
fg_waitkey();
fg_palette(1,15);
fg_waitkey();
fg_setmode(mode);
fg_reset();
}
Chapter 5: The Use of Color 83
VGA/SVGA 16-Color Modes
The VGA and SVGA 16-color modes (modes 18, 28, and 29) have 16 color
values, numbered 0 to 15. Each color value references one of 16 user-definable
palette registers, often simply called palettes, also numbered 0 to 15. Each
palette register in turn references one of 16 user-definable 18-bit video DAC
registers, also numbered 0 to 15. The values assigned to the palette registers
and video DAC registers determine the colors in which pixels are displayed.
For example, if palette register 1 contains the value 3, and video DAC
register 3 contains the color value for red, then pixels whose color value is
1 will be red.
By default, each of the 16 palette registers references the video DAC
register of the same number. In addition, the 16 video DAC registers
respectively contain the color values for the 16 colors in the standard color
set.
The 18-bit video DAC values consist of three 6-bit red, green, and blue
color components. Hence, each color component is an integer between 0 and 63;
increasing values produce more intense colors. The default RGB color
components for the 16 video DAC registers are:
DAC R G B color DAC R G B color
0 0 0 0 black 8 21 21 21 dark gray
1 0 0 42 blue 9 21 21 63 light blue
2 0 42 0 green 10 21 63 21 light green
3 0 42 42 cyan 11 21 63 63 light cyan
4 42 0 0 red 12 63 21 21 light red
5 42 0 42 magenta 13 63 21 63 light magenta
6 42 21 0 brown 14 63 63 21 yellow
7 42 42 42 gray 15 63 63 63 white
Because the video DAC registers are 18 bits long, each DAC can specify one of
262,144 (2**18) colors. However, because the palette registers hold 4-bit
quantities, only 16 of these colors can be displayed at the same time. In
other words, mode 18 provides the capability of displaying 16 simultaneous
colors from a group of 262,144.
In the 16-color VGA and SVGA modes, fg_setcolor, fg_palette, and
fg_setrgb behave exactly as in mode 17 with one exception: there are 16
palette registers instead of just two. Example 5-9 demonstrates the use of
these routines in mode 17, but it also would work in mode 18, 28, or 29 if the
call to fg_setmode were changed accordingly.
256-Color Modes
The 256-color modes (modes 19 through 27) have 256 color values, numbered
0 to 255. Each color value directly references one of 256 user-definable 18-
bit video DAC registers, also numbered 0 to 255. The values assigned to the
video DAC registers determine the colors in which pixels are displayed. For
example, if video DAC register 3 contains the color value for red, then pixels
whose color value is 3 will be red.
84 Fastgraph User's Guide
By default, the first 16 video DAC registers (0 to 15) contain the color
values for the standard color set. The next 16 DAC registers (16 to 31)
contain the color values for a gray scale of gradually increasing intensity.
The next 216 DAC registers (32 to 247) contain three groups of 72 colors each,
with the first group (32 to 103) at high intensity, the second group (104 to
175) at moderate intensity, and the third group (176 to 247) at low intensity.
Each group consists of three ranges of decreasing saturation (increasing
whiteness), with each range varying in hue from blue to red to green. Finally,
the last 8 DAC registers (248 to 255) alternate between black and white. This
information is summarized in the following table.
DACs default color values
0 to 15 standard color set
16 to 31 gray scale of gradually increasing intensity
32 to 55 high saturation, high intensity colors
56 to 79 moderate saturation, high intensity colors
80 to 103 low saturation, high intensity colors
104 to 127 high saturation, moderate intensity colors
128 to 151 moderate saturation, moderate intensity colors
152 to 175 low saturation, moderate intensity colors
176 to 199 high saturation, low intensity colors
200 to 223 moderate saturation, low intensity colors
224 to 247 low saturation, low intensity colors
248 to 255 alternate between black and white
The 18-bit video DAC values consist of three 6-bit red, green, and blue
color components. Hence, each color component is an integer between 0 and 63;
increasing values produce more intense colors. Because the video DAC registers
are 18 bits long, each DAC can specify one of 262,144 (2**18) colors. However,
because the color values are 8-bit quantities, only 256 of these colors can be
displayed at the same time. In other words, modes 19 through 27 provide the
capability of displaying 256 simultaneous colors from a group of 262,144.
In the 256-color graphics modes, fg_setcolor defines the current color by
referencing one of the 256 video DAC registers. The fg_setrgb routine defines
the actual color of a video DAC register. The first argument of fg_setrgb is
an integer between 0 and 255 that specifies the DAC register number. The
remaining three arguments are each integer values between 0 and 63 that
respectively specify the red, green, and blue color components for that DAC
register. Another Fastgraph routine, fg_getrgb, returns the color components
for a specified DAC register. Its arguments are the same as for fg_setrgb,
except the last three arguments (the return values) are passed by reference
rather than by value.
You also can use the Fastgraph routine fg_palette to define the value of
a video DAC register in modes 19 through 27. The first argument of fg_palette
is an integer between 0 and 255 that specifies the DAC register number. The
second argument is an integer between 0 and 63 that specifies the color value
for that video DAC register, using the same 64 values as in the EGA enhanced
mode (mode 16).
Example 5-10 demonstrates the use of fg_setcolor in mode 19. The program
uses the Fastgraph routine fg_rect to draw vertical lines. After establishing
the video mode, the program uses a for loop to draw 256 vertical lines, one in
Chapter 5: The Use of Color 85
each of the 256 colors (using the default DAC values). Finally, the program
restores the original video mode and screen attributes before returning to
DOS.
Example 5-10.
#include <fastgraf.h>
void main(void);
#define COLORS 256
void main()
{
int base;
int color;
int mode;
int x;
fg_initpm();
mode = fg_getmode();
fg_setmode(19);
x = 0;
for (color = 0; color < COLORS; color++) {
fg_setcolor(color);
fg_rect(x,x,0,199);
x++;
}
fg_waitkey();
fg_setmode(mode);
fg_reset();
}
Example 5-11 shows an interesting effect available in video modes that
support DAC registers. The program uses the Fastgraph routine fg_waitfor
(discussed in Chapter 16) to delay the program's execution. After establishing
the video mode, the program displays the word "Hello" in color 103, which by
default is a pastel blue. It then uses fg_getrgb to retrieve the color
components for this color. The while loop gradually decreases the color
components until all three components are zero, which makes the word "Hello"
smoothly fade to black. Finally, the program restores the original video mode
and screen attributes before returning to DOS.
Example 5-11.
#include <fastgraf.h>
void main(void);
void main()
{
int old_mode;
int red, green, blue;
86 Fastgraph User's Guide
fg_initpm();
old_mode = fg_getmode();
fg_setmode(19);
fg_setcolor(103);
fg_text("Hello",5);
fg_waitfor(18);
fg_getrgb(103,&red,&green,&blue);
while (red+green+blue > 0) {
if (red > 0) red--;
if (green > 0) green--;
if (blue > 0) blue--;
fg_setrgb(103,red,green,blue);
fg_waitfor(1);
}
fg_setmode(old_mode);
fg_reset();
}
The fg_setrgb and fg_getrgb routines work with individual DAC registers.
If you want to define or retrieve a block of consecutive DAC registers,
fg_setdacs and fg_getdacs are more efficient. The fg_setdacs routine defines
the values of a block of consecutive DAC registers. Its first argument is the
index of the first DAC register to define (between 0 and 255), and its second
argument is the number of DAC registers to define (between 1 and 256). The
third argument is a byte array containing the RGB color components for the DAC
registers being defined. The array's first three bytes contain the red, green,
and blue components for the first DAC, the next three for the second DAC, and
so forth. The size of this array must be at least three times the value of the
second argument. The fg_getdacs arguments are the same as those for
fg_setdacs, but the RGB array instead receives the current values of the
specified DAC registers. Both routines treat the DAC register numbers in a
circular fashion (for example, defining four DACs starting with number 254
will define DACs 254, 255, 0, and 1).
Example 5-12 is similar to example 5-11, but it fades many colors
simultaneously. The program displays seven asterisks, one each in colors 9
through 15. It uses fg_getdacs to obtain the current settings of the
corresponding DAC registers; these values are stored in the array RGBvalues.
The while loop gradually fades the RGB components to zero, using fg_setdacs to
update their values, similar to the method of example 5-11. This illustrates
an attractive way of turning an image into a blank screen.
Example 5-12.
#include <fastgraf.h>
void main(void);
void main()
{
int decreasing;
int i;
Chapter 5: The Use of Color 87
int old_mode;
char RGBvalues[21];
fg_initpm();
old_mode = fg_getmode();
fg_setmode(19);
for (i = 9; i <= 15; i++) {
fg_setcolor(i);
fg_text("*",1);
}
fg_getdacs(9,7,RGBvalues);
fg_waitfor(18);
do {
decreasing = 0;
for (i = 0; i < 21; i++)
if (RGBvalues[i] > 0) {
RGBvalues[i]--;
decreasing = 1;
}
fg_setdacs(9,7,RGBvalues);
fg_waitfor(1);
}
while (decreasing);
fg_setmode(old_mode);
fg_reset();
}
Note that examples 5-11 and 5-12 also would work in 16-color VGA and SVGA
video modes as long as you just use the first 16 video DAC registers.
Using Video DAC Registers in EGA Modes
The fg_getdacs and fg_setdacs routines also work in modes 13, 14, and 16
when used on a VGA or SVGA system. This lets you choose 16 colors from a
palette of 262,144 colors, as in mode 18. If you try to use these routines on
an EGA system, the results are unpredictable. Applications that use these
routines should therefore first insure they are running on a VGA or SVGA
system by checking if fg_testmode(18,0) returns a nonzero value.
Before trying to use fg_getdacs and fg_setdacs in modes 13, 14, and 16,
you should first be aware of the relationship between VGA palettes and DAC
registers. On the EGA, palette values directly determine the color displayed.
On the VGA and SVGA, however, there is an added level of indirection. VGA and
SVGA palette registers can be thought of as pointers to video DAC registers
whose RGB components determine the displayed color.
Each palette register in the VGA 640x480 16-color graphics mode (mode 18)
initially points to the DAC register of the same number. We can thus pretend
the indirection does not exist because changing DAC register n affects those
pixels whose color value is n (unless, of course, we've changed the value of
88 Fastgraph User's Guide
palette register n). In modes 13, 14, and 16, we can't ignore the indirection
because the palette registers contain different values. In mode 13, for
instance, palette register 8 contains the value 16 by default, not the value 8
as in mode 18.
The easiest way around this inconsistency is to set the palette and DAC
registers explicitly so they correspond to the default values of mode 18.
There are two cases to consider -- one for modes 13 and 14, and the other for
mode 16.
In modes 13 and 14, palettes 0 to 7 contain the values 0 to 7, but
palettes 8 to 15 contain the values 16 to 23. Hence, if you want to use
fg_getdacs and fg_setdacs in these modes, you should include the following
code after calling fg_setmode.
char RGBvalues[3];
int i;
for (i = 8; i < 16; i++) {
fg_getdacs(i+8,1,RGBvalues);
fg_setdacs(i,1,RGBvalues);
fg_palette(i,i);
}
This code will set the values of DACs 8 to 15 to the values of DACs 16 to 23.
It also sets palettes 8 to 15 to point to DACs 8 to 15. You can then ignore
the palette-DAC indirection because setting DAC register n affects pixels of
color n.
In mode 16, palette 6 is initially assigned the value 20, and palettes 8
to 15 are assigned the values 56 to 63. All other palettes point to the DAC of
the same number. Hence, if you want to use fg_getdacs and fg_setdacs in mode
16, you should include the following code after calling fg_setmode.
char RGBvalues[3];
int i;
fg_getdacs(20,1,RGBvalues);
fg_setdacs(6,1,RGBvalues);
fg_palette(6,6);
for (i = 8; i < 16; i++) {
fg_getdacs(i+48,1,RGBvalues);
fg_setdacs(i,1,RGBvalues);
fg_palette(i,i);
}
This code will set the values of DAC 6 to the values of DAC 20, and also DACs
8 to 15 to the values of DACs 56 to 63. It also sets palettes 6 and 8-15 to
point to the identically-numbered DACs. You can then ignore the palette-DAC
indirection because setting DAC register n affects pixels of color n.
Chapter 5: The Use of Color 89
While this might all seem complicated at first, it really isn't once you
understand the relationship between palettes and DACs. The ability to select
colors from a palette of 256K colors instead of 16 or 64 is usually well worth
the extra effort.
RGB Color Mapping
If you're developing an application that runs in 256-color and 16-color
graphics modes, you've probably noticed the inherent differences in defining
color values. In fact, the palette register values even use different
structures within the various 16-color modes. The Fastgraph routine fg_maprgb
helps simplify these differences. It maps three RGB color components (each
between 0 and 63) into a 16-color palette value suitable for the current video
mode. Of course, the range of available colors is much more restricted in the
16-color modes than in the 256-color modes, so fg_maprgb must map the RGB
components to the closest available color.
Example 5-13 runs in any 16-color or 256-color graphics mode and
demonstrates the use of the fg_maprgb routine. In 256-color modes, the program
simply uses fg_setrgb to define DAC register 1 to a pastel blue (red=45,
green=49, blue=63). In 16-color modes, however, the program calls fg_maprgb to
convert the color components into a palette value in IRGB, IxRGB, or rgbRGB
format (depending on the current video mode). The fg_maprgb return value is
passed to fg_palette to set palette register 1 to the closest available color
defined by the specified RGB components.
Example 5-13.
#include <fastgraf.h>
#include <stdio.h>
#include <stdlib.h>
void main(void);
void main()
{
int new_mode, old_mode;
fg_initpm();
new_mode = fg_bestmode(320,200,1);
if (new_mode < 0 || new_mode == 4 || new_mode == 12) {
printf("This program requires a 320 x 200 ");
printf("16-color or 256-color graphics mode.\n");
exit(1);
}
old_mode = fg_getmode();
fg_setmode(new_mode);
fg_setcolor(1);
if (new_mode <= 16)
fg_palette(1,fg_maprgb(45,49,63));
else
fg_setrgb(1,45,49,63);
fg_text("Hello",5);
fg_waitkey();
90 Fastgraph User's Guide
fg_setmode(old_mode);
fg_reset();
}
Defining All Palette Registers
Fastgraph includes a routine fg_palettes that defines all 16 palette
registers in 16-color graphics modes. You also can use fg_palettes to define
the first 16 video DAC registers in 256-color modes. It has no effect in other
video modes.
Using fg_palettes is much faster than calling fg_palette 16 times. The
argument to fg_palettes is a 16-element integer array that contains the color
values assigned respectively to palette registers (or video DAC registers) 0
to 15. Example 5-14 demonstrates how to zero the palette registers (that is,
change them all to black) in mode 13.
Example 5-14.
#include <fastgraf.h>
void main(void);
int zeroes[] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
void main()
{
int mode;
fg_initpm();
mode = fg_getmode();
fg_setmode(13);
fg_palettes(zeroes);
fg_setmode(mode);
fg_reset();
}
Of course, as this example is written, it appears to do nothing more than
blank the screen. Its purpose is to show an example of the fg_palettes
routine.
Virtual Colors
By this time it should be clear the use of color is rather specific to
each graphics video mode. One of the most obvious differences is the number of
available colors in each mode; it ranges from 2 to 256. By available colors,
we mean the number of colors that can be displayed simultaneously.
To simplify programming in graphics modes, Fastgraph provides 256 virtual
colors. The virtual colors are used in the graphics video modes having fewer
than 256 available colors. Virtual colors allow you to use 256 color indices
Chapter 5: The Use of Color 91
in all graphics modes, even if a particular mode does not have 256 available
colors.
When you establish a video mode with fg_setmode, Fastgraph initializes
all the virtual color indices. It does this by replicating the video mode's
color values through the 256 virtual color indices. For example, the CGA color
modes (4 and 5) have four color values, numbered 0 through 3. In these modes,
fg_setmode initializes color indices 0, 4, 8, ... , 252 to 0; color indices 1,
5, 9, ... , 253 to 1; color indices 2, 6, 10, ... , 254 to 2; and color
indices 3, 7, 11, ... , 255 to 3. Similarly, in 16-color graphics modes the
color indices 0, 16, 32, ... , 240 are set to 0, and so forth. In the
monochrome EGA graphics video mode (mode 15), the color values are numbered 0,
1, 4, and 5, so fg_setmode replicates the color indices in groups of eight,
even though there are only four available colors. An analysis of the color
value sequences reveals an often useful feature: by default, virtual color 0
is black and virtual colors 15 and 255 are white in all graphics video modes.
It is thus possible to write a multiple-mode program using the same color
indices for each graphics mode. For example, a program that contains the
statement fg_setcolor(5) would produce subsequent graphics in color 5 (magenta
by default) when running in a 16-color graphics mode. It would produce
subsequent graphics in color 1 (light cyan by default) when running in a CGA
color mode. This is because 1 is the default value assigned to virtual color
index 5 in the CGA color modes.
The fg_setmode routine establishes default values for the 256 virtual
color indices, but it might be desirable to assign other available colors to
them. Going back to the discussion in the previous paragraph, color number 2
is light magenta in the default CGA mode 4 palette. It might make more sense
if the color value 2 were assigned to virtual color index 5, as this would
make the graphics drawn in color 5 the same color in mode 4 as in other color
modes. The Fastgraph routine fg_defcolor is provided for this purpose.
The fg_defcolor routine assigns a color value to a virtual color index.
It has two arguments: the first specifies the virtual color index (between 0
and 255), and the second specifies the color value (between 0 and one less
than the number of available colors in the current video mode). For example,
the statement
fg_defcolor(5,2);
would assign the color value 2 to the color index 5. Another Fastgraph
routine, fg_getindex, returns the current value assigned to a specified color
index. After executing the above call to fg_defcolor, the statement
color = fg_getindex(5);
would store the value 2 (the current value of color index 5) in the integer
variable color.
We must be sure to understand the difference between virtual colors and
palette registers. Modifying the value of a palette register changes the color
of all pixels already drawn using that palette. Modifying a virtual color
index does not do this; it only specifies any graphics drawn in that color
from this point on will appear in the new color.
92 Fastgraph User's Guide
Example 5-15 demonstrates virtual colors in mode 4. After establishing
the video mode, the program uses fg_defcolor to define virtual color indices 0
and 255 to be 1, which by default is light cyan in mode 4. It then draws
characters using color indices 0, 1, and 255, and in each case the characters
appear in light cyan. Finally, the program restores the original video mode
and screen attributes before returning to DOS.
Example 5-15.
#include <fastgraf.h>
void main(void);
void main()
{
int mode;
fg_initpm();
mode = fg_getmode();
fg_setmode(4);
fg_defcolor(0,1);
fg_defcolor(255,1);
fg_setcolor(0);
fg_text("0",1);
fg_setcolor(1);
fg_text(" 1",2);
fg_setcolor(255);
fg_text(" 255",4);
fg_waitkey();
fg_setmode(mode);
fg_reset();
}
A Multiple-Mode Example
Although the color capabilities differ between the supported video modes,
Fastgraph makes it easy to write a program that runs in many video modes. This
section will present an example of such a program.
Example 5-16 illustrates a program that will run in any of Fastgraph's
supported video modes. The program first asks for the video mode number,
checks if the mode number is valid, and then checks if the requested mode is
available on the user's system. After doing this, the program establishes the
video mode and performs its mode-specific code. It then displays a brief
message that includes the video mode number in which the program is running.
This information remains on the screen until a key is pressed, at which time
the program restores the original video mode and screen attributes before
returning to DOS.
Example 5-16.
#include <fastgraf.h>
Chapter 5: The Use of Color 93
#include <stdio.h>
#include <stdlib.h>
void main(void);
void main()
{
int mode, old_mode;
char string[5];
/* Ask for the video mode number */
printf("Which video mode? ");
scanf("%d",&mode);
/* Make sure the entered value is valid */
if (mode < 0 || mode > 29) {
printf("%d is not a valid video mode number.\n",mode);
exit(1);
}
/* Make sure the requested video mode is available */
fg_initpm();
if (mode > 23) fg_svgainit(0);
if (fg_testmode(mode,1) == 0) {
printf("Mode %d is not available on this system.\n",mode);
exit(1);
}
/* Establish the video mode */
old_mode = fg_getmode();
fg_setmode(mode);
/* Perform mode-specific initializations */
if (mode <= 3 || mode == 7) /* text modes */
fg_cursor(0);
else if (mode == 4 || mode == 5) { /* CGA color modes */
fg_palette(0,0);
fg_defcolor(14,3);
}
else if (mode == 6) { /* CGA two-color mode */
fg_palette(0,14);
fg_defcolor(14,1);
}
else if (mode == 11) /* Hercules mode */
fg_defcolor(14,1);
else if (mode == 12) /* Hercules low-res mode */
fg_defcolor(14,3);
else if (mode == 17) { /* VGA two-color mode */
fg_palette(1,14);
fg_setrgb(14,63,63,21);
fg_defcolor(14,1);
}
94 Fastgraph User's Guide
/* Display a message that includes the video mode number */
fg_setcolor(14);
fg_text("I'm running in mode ",20);
sprintf(string,"%d. ",mode);
fg_text(string,3);
/* Wait for a keystroke */
fg_waitkey();
/* Restore the original video mode and screen attributes */
fg_setmode(old_mode);
fg_reset();
}
Example 5-16 displays its message in yellow for those video modes that
offer color. In monochrome video modes, it displays the message in normal
intensity. The program uses virtual color 14, which by default is yellow in
many video modes; the mode-specific code in example 5-16 makes color 14 yellow
in other video modes. In text video modes (modes 0 to 3 and 7), the program
uses fg_cursor to make the cursor invisible. In CGA color modes (modes 4 and
5), the program uses fg_palette to select a CGA palette that contains yellow
as color 3 and then uses fg_defcolor to assign color 3 to virtual color 14. In
CGA two-color mode (mode 6), the program uses fg_palette to make color 1
yellow and then uses fg_defcolor to assign color 1 to virtual color 14. In the
Hercules modes (modes 11 and 12), the program uses fg_defcolor to assign the
value for normal intensity pixels to color 14. In VGA two-color mode (mode
17), the program uses fg_palette to assign video DAC register 14 to palette
register 1. It then defines video DAC register 14 to be yellow with fg_setrgb
and finally uses fg_defcolor to assign color 1 (that is, palette register 1)
to virtual color 14. In all other video modes, no color manipulation is needed
because color 14 is yellow by default.
Summary of Color-Related Routines
This section summarizes the functional descriptions of the Fastgraph
routines presented in this chapter. More detailed information about these
routines, including their arguments and return values, may be found in the
Fastgraph Reference Manual.
FG_COLORS returns the number of simultaneously available colors in the
current video mode. In text video modes, fg_colors returns zero.
FG_DEFCOLOR assigns a color value to a virtual color index. This routine
is only meaningful in graphics video modes that have fewer than 256 available
colors.
FG_GETCOLOR returns the current text attribute (in text modes) or color
index (in graphics modes), as specified in the most recent call to fg_setattr
or fg_setcolor.
FG_GETDACS retrieves the red, green, and blue color components for a
block of consecutively numbered video DAC registers. This routine is only
meaningful modes that use DAC registers.
Chapter 5: The Use of Color 95
FG_GETINDEX returns the color value assigned to a specified virtual color
index. In text modes and in graphics modes that have 256 available colors,
this routine returns the value passed to it.
FG_GETRGB returns the red, green, and blue color components for a
specified video DAC register. This routine is only meaningful in modes that
use DAC registers.
FG_MAPRGB maps six-bit red, green, and blue color components into a
suitable palette value for the current video mode. You can then pass this
value to fg_palette. This routine is meaningful only in 16-color graphics
video modes.
FG_PALETTE has different functions depending on the current graphics
video mode. For the CGA four-color modes, it establishes the current palette
(of six available) and defines the background color for that palette. In the
CGA two-color mode, it defines the foreground color. For the Tandy/PCjr, EGA,
and VGA graphics modes, it defines the value of a single palette register. For
256-color graphics modes, it defines the value of a single video DAC register.
The fg_palette routine has no effect in text modes or Hercules graphics modes.
FG_PALETTES defines all 16 palette registers (in 16-color graphics
modes), or the first 16 video DAC registers (in 256-color graphics modes). The
fg_palettes routine has no effect in text modes, CGA graphics modes, or
Hercules graphics modes.
FG_SETATTR establishes the current text attribute in text video modes.
This routine has no effect in graphics modes.
FG_SETCOLOR establishes the current color index (which may be a virtual
color index in graphics modes). In text modes, fg_setcolor provides an
alternate method of establishing the current text attribute.
FG_SETDACS defines the values of a block of consecutively numbered video
DAC registers by specifying their red, green, and blue color components. This
routine is only meaningful in modes that use DAC registers.
FG_SETRGB defines the value of a single palette register (in Tandy/PCjr
and EGA graphics modes) or video DAC register (in VGA, MCGA, and SVGA modes)
by specifying its red, green, and blue color components. The fg_setrgb routine
has no effect in text modes, CGA graphics modes, or Hercules graphics modes.
96 Fastgraph User's Guide
