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Chapter 6
Graphics Fundamentals
98 Fastgraph User's Guide
Overview
This chapter describes Fastgraph's fundamental graphics routines,
sometimes called graphics primitives. These routines perform such functions
as clearing the screen, drawing points, drawing solid and dashed lines,
drawing closed shapes (polygons, circles, and ellipses), drawing rectangles
(solid, hollow, and dithered), and filling arbitrary regions. Most of these
routines have no effect in text video modes, but there are a few exceptions,
and they will be noted in the descriptions of those routines.
Clearing the Screen
The Fastgraph routine fg_erase clears the entire screen in any video
mode. In text modes, fg_erase stores a space character (ASCII 32) with a
gray foreground attribute in each character cell. In graphics modes,
fg_erase sets each pixel to zero. This of course causes each pixel to be
displayed its background color. The fg_erase routine has no arguments.
The fg_erase routine always sets the entire screen to the background
color. Another routine, fg_fillpage, fills the screen with the current
color. In text modes, fg_fillpage stores a solid block character (ASCII 219)
with the current display attribute (as defined in the most recent call to
fg_setcolor or fg_setattr). In graphics modes, fg_fillpage sets each pixel
to the current color (as defined in the most recent call to fg_setcolor).
Like fg_erase, the fg_fillpage routine has no arguments.
Clipping
The suppression of graphics outside a pre-defined area is called
clipping. Many of Fastgraph's graphics-oriented routines provide clipping,
either automatically or through a special version of the routine.
Fastgraph includes two routines, fg_setclip and fg_setclipw, to define a
rectangular clipping region. The fg_setclip routine defines the clipping
region in screen space, while the fg_setclipw routine performs the same
function in world space. Each routine takes four arguments: the minimum x,
the maximum x, the minimum y, and the maximum y coordinate of the clipping
region. The arguments are integer quantities for fg_setclip and floating
point quantities for fg_setclipw. For example, the statement
fg_setclip(0,159,0,99);
would define the upper left quadrant of the screen as the clipping region in
a 320 by 200 graphics mode.
An implicit clipping region equal to the entire screen is defined as
part of the fg_setmode routine's initializations. Clipping is not supported
for text modes.
Chapter 6: Graphics Fundamentals 99
Points
The Fastgraph routine fg_point provides the most basic graphics
operation -- setting a pixel to a specified color. The fg_point routine has
two integer arguments. The first specifies the pixel's x coordinate, and the
second its y coordinate. The pixel is drawn using the current color value,
as specified in the most recent call to fg_setcolor. There is also a world
space version of this routine, fg_pointw, that uses floating point arguments.
Another Fastgraph routine is available for reading a pixel's color
value. The fg_getpixel routine has two integer arguments that specify the
(x,y) coordinates for the pixel of interest. There is no world space version
of the fg_getpixel routine, but you can obtain a pixel's color value in world
space by applying the fg_xscreen and fg_yscreen functions to the world space
coordinates and passing the resulting values to fg_getpixel.
Example 6-1 uses the fg_point routine to draw 100 random points in
random colors. It also uses the fg_getpixel routine to insure no two points
are adjacent. The program establishes a graphics video mode with the
fg_automode and fg_setmode routines. Next, it determines the maximum color
value for the selected video mode; note if we used virtual colors (color
indices above the maximum color value), some of the colors would be the
background color and would thus produce invisible points. The main part of
the program is a while loop that first generates a random pair of (x,y)
screen coordinates. It then calls the fg_getpixel routine to check the
pixels at (x,y) and the eight adjacent positions. If none of these pixels
are set, the program generates a random color value and draws a point in that
color. After doing this 100 times, the program waits for a keystroke,
restores the original video mode and screen attributes, and then returns to
DOS.
Example 6-1.
#include <fastgraf.h>
#include <stdlib.h>
void main(void);
void main()
{
int area;
int color, old_color;
int left;
int max_color, max_x, max_y;
int new_mode, old_mode;
100 Fastgraph User's Guide
int x, y;
old_mode = fg_getmode();
new_mode = fg_automode();
fg_setmode(new_mode);
if (new_mode == 4)
max_color = 3;
else if (new_mode == 11 || new_mode == 17)
max_color = 1;
else if (new_mode == 19)
max_color = 255;
else
max_color = 15;
left = 100;
max_x = fg_getmaxx() - 1;
max_y = fg_getmaxy() - 1;
while (left > 0) {
x = rand() % max_x + 1;
y = rand() % max_y + 1;
area = fg_getpixel(x-1,y-1)+fg_getpixel(x,y-1)+fg_getpixel(x+1,y-1)
+ fg_getpixel(x-1,y) +fg_getpixel(x,y) +fg_getpixel(x+1,y)
+ fg_getpixel(x-1,y+1)+fg_getpixel(x,y+1)+fg_getpixel(x+1,y+1);
Chapter 6: Graphics Fundamentals 101
if (area == 0) {
color = rand() % max_color + 1;
fg_setcolor(color);
fg_point(x,y);
left--;
}
}
fg_waitkey();
fg_setmode(old_mode);
fg_reset();
}
Sometimes you may want to display a pixel using an "exclusive or"
operation (usually called XOR) to guarantee its visibility. The color of a
pixel drawn in XOR mode will be c xor p, where c is the current color and p
is the color of the pixel already at that position. This means the pixel's
new color will be different from the background as long as the current color
is not zero. The Fastgraph routine fg_pointx displays a screen space pixel
in XOR mode, while fg_pointxw does the same thing in world space. Their
respective parameters are the same as for fg_point and fg_pointw.
The Graphics Cursor
Many of Fastgraph's graphics routines depend on the position of the
graphics cursor as a reference point. For example, Fastgraph includes
routines to draw lines from the graphics cursor position to a specified
position, and the bit-mapped image display routines discussed in Chapter 10
display or retrieve an image relative to the graphics cursor position. The
graphics cursor is not a cursor in the true sense; it is simply a pair of
(x,y) coordinates with a special meaning. The fg_setmode routine sets the
graphics cursor position to the screen space coordinates (0,0), and the
fg_initw routine sets it to the world space coordinates (0.0,0.0).
Fastgraph includes four routines for changing the graphics cursor
position. The fg_move routine sets it to an absolute screen space position,
while the fg_movew routine sets it to an absolute world space position. The
fg_moverel routine sets the graphics cursor position to a screen space
position relative to its current position. The fg_moverw routine does the
same in world space.
102 Fastgraph User's Guide
Each of these routines has two arguments that specify the (x,y)
coordinates of the new position. For the screen space routines, the
arguments are integer quantities. For the world space routines, the
arguments are floating point quantities.
You can obtain the screen space coordinates of the graphics cursor
position with the fg_getxpos and fg_getypos routines. These routines have no
arguments and respectively return the x and y coordinates of the graphics
cursor position as the function value. To obtain the world space coordinates
of the graphics cursor position, you can apply the fg_xworld and fg_yworld
functions to the return values of fg_getxpos and fg_getypos.
Solid Lines
Fastgraph includes eight routines for drawing solid lines. All of them
draw lines in the current color value and observe the clipping limits. The
fg_draw routine draws a line from the current graphics cursor position to an
absolute screen space position, while fg_draww draws a line to an absolute
world space position. The fg_drawrel routine draws a line from the current
graphics cursor position to a screen space position relative to it. The
fg_drawrw routine does the same in world space. You can draw absolute lines
in XOR mode with fg_drawx and relative XOR lines with fg_drawrelx, or with
their world space counterparts fg_drawxw and fg_drawrxw. XOR lines are often
used when drawing cursors (such as cross hairs) or rubberband boxes to insure
they are visible against colored backgrounds. Another useful property of XOR
lines is that drawing the same lines twice restores what was originally
beneath the lines.
Each of these routines has two arguments that specify the (x,y)
coordinates of the destination position. For the screen space routines, the
arguments are integer quantities. For the world space routines, the
arguments are floating point quantities. In either case the destination
position becomes the new graphics cursor position. This makes it possible to
draw connected lines without calling a graphics cursor movement routine
between successive calls to a line drawing routine.
Examples 6-2 and 6-3 each draw a pair of crossed lines that divide the
screen into quadrants. Example 6-2 does this using the fg_move and fg_draw
routines, while example 6-3 uses the fg_moverel and fg_drawrel routines.
Both examples draw the lines in white, the default for color 15 in all
graphics video modes.
Example 6-2. Example 6-3.
#include <fastgraf.h> #include <fastgraf.h>
void main(void); void main(void);
void main() void main()
{ {
int max_x, max_y; int max_x, max_y;
int mid_x, mid_y; int mid_x, mid_y;
int new_mode, old_mode; int new_mode, old_mode;
old_mode = fg_getmode(); old_mode = fg_getmode();
new_mode = fg_automode(); new_mode = fg_automode();
Chapter 6: Graphics Fundamentals 103
fg_setmode(new_mode); fg_setmode(new_mode);
max_x = fg_getmaxx(); max_x = fg_getmaxx();
max_y = fg_getmaxy(); max_y = fg_getmaxy();
mid_x = max_x / 2; mid_x = max_x / 2;
mid_y = max_y / 2; mid_y = max_y / 2;
fg_setcolor(15); fg_setcolor(15);
fg_move(mid_x,0); fg_move(mid_x,0);
fg_draw(mid_x,max_y); fg_drawrel(0,max_y);
fg_move(0,mid_y); fg_moverel(-mid_x,-mid_y);
fg_draw(max_x,mid_y); fg_drawrel(max_x,0);
fg_waitkey(); fg_waitkey();
fg_setmode(old_mode); fg_setmode(old_mode);
fg_reset(); fg_reset();
} }
Examples 6-4 and 6-5 are variations of example 6-2. Example 6-4 uses
world space rather than screen space to draw the crossed lines. Example 6-5
is the same as example 6-2 except it defines a clipping area to restrict
drawing to the upper left quadrant of the screen. The clipping suppresses
the right half of the horizontal line and the lower half of the vertical
line.
Example 6-4. Example 6-5.
#include <fastgraf.h> #include <fastgraf.h>
void main(void); void main(void);
void main() void main()
{ {
int new_mode, old_mode; int max_x, max_y;
int mid_x, mid_y;
old_mode = fg_getmode(); int new_mode, old_mode;
new_mode = fg_automode();
fg_setmode(new_mode); old_mode = fg_getmode();
fg_initw(); new_mode = fg_automode();
fg_setworld(-10.0,10.0,-10.0,10.0); fg_setmode(new_mode);
104 Fastgraph User's Guide
fg_setcolor(15); max_x = fg_getmaxx();
fg_movew(0.0,10.0); max_y = fg_getmaxy();
fg_draww(0.0,-10.0); mid_x = max_x / 2;
fg_movew(-10.0,0.0); mid_y = max_y / 2;
fg_draww(10.0,0.0);
fg_waitkey(); fg_setclip(0,mid_x,0,mid_y);
fg_setmode(old_mode); fg_setcolor(15);
fg_reset(); fg_move(mid_x,0);
} fg_draw(mid_x,max_y);
fg_move(0,mid_y);
fg_draw(max_x,mid_y);
fg_waitkey();
fg_setmode(old_mode);
fg_reset();
}
Dashed Lines
Fastgraph includes four routines for drawing dashed lines. All of them
draw lines in the current color value and observe the clipping limits. The
fg_dash routine draws a dashed line from the current graphics cursor position
to an absolute screen space position, while fg_dashw draws a dashed line to
an absolute world space position. The fg_dashrel routine draws a dashed line
from the current graphics cursor position to a screen space position relative
to it. The fg_dashrw routine does the same in world space.
Each of these routines has three arguments. The first two specify the
(x,y) coordinates of the destination position. For the screen space
routines, these arguments are integer quantities. For the world space
routines, these arguments are floating point quantities. The third argument
is a 16-bit pattern that defines the appearance of the dashed line. Bits
that are set in the pattern produce the visible part of the line, while bits
that are reset produce the invisible part. This pattern is repeated as
necessary to draw the entire line. For example, the pattern value 3333 hex
would produce a dashed line with the first two pixels off, the next two on,
Chapter 6: Graphics Fundamentals 105
the next two off, and so forth. Similarly, the pattern value FFFF hex would
produce a solid line.
The destination position passed to any of the dashed line routines
becomes the new graphics cursor position. This makes it possible to draw
connected dashed lines without calling a graphics cursor movement routine
between successive calls to a line drawing routine.
Example 6-6 draws a pair of crossed dashed lines that divide the screen
into quadrants. It does this using the fg_move and fg_dash routines and
draws the lines in white, the default for color 15 in all graphics video
modes. The dash pattern for each line is 3333 hex, which alternates two
pixels off and on.
Example 6-6.
#include <fastgraf.h>
void main(void);
void main()
{
int max_x, max_y;
int mid_x, mid_y;
int new_mode, old_mode;
old_mode = fg_getmode();
new_mode = fg_automode();
fg_setmode(new_mode);
max_x = fg_getmaxx();
max_y = fg_getmaxy();
mid_x = max_x / 2;
mid_y = max_y / 2;
fg_setcolor(15);
fg_move(mid_x,0);
fg_dash(mid_x,max_y,0x3333);
fg_move(0,mid_y);
fg_dash(max_x,mid_y,0x3333);
fg_waitkey();
fg_setmode(old_mode);
fg_reset();
}
Polygons
Fastgraph includes routines for drawing filled and unfilled polygons, as
well as a routine for determining if a given point is inside a convex
polygon. All the polygon routines observe the clipping limits.
The fg_polygon routine draws an unfilled polygon in screen space.
Fg_polygon requires an array of integer x coordinates as its first argument,
and an array of integer y coordinates as its second argument. Each (x,y)
coordinate pair from the two arrays is treated as a polygon vertex. In other
106 Fastgraph User's Guide
words, the x coordinate of the first polygon vertex is the first element of
the x coordinate array, and the y coordinate of the first vertex is the first
element of the y coordinate array. Similarly, the second elements of each
array define the second vertex, and so forth. The third argument for
fg_polygon is an integer quantity that specifies the number of elements in
the two coordinate arrays (that is, the number of polygon vertices).
Another routine, fg_polygonw, draws an unfilled polygon in world space.
The fg_polygonw routine is the same as the fg_polygon routine, except its x
and y coordinate arrays must contain floating point values instead of
integers.
The polygon drawing begins at the first vertex specified in the
coordinate arrays. The polygon routines then draw a solid line to the second
vertex, then to the third vertex, and continue in this manner through the
last vertex. If necessary, they then close the polygon by drawing a line
connecting the last vertex and the first vertex. Example 6-7 illustrates
unfilled polygon drawing using the fg_polygon routine in the EGA monochrome
or enhanced modes (modes 15 and 16). The program exits if neither of these
video modes are available.
Example 6-7.
#include <fastgraf.h>
#include <stdio.h>
#include <stdlib.h>
void main(void);
#define VERTICES 10
int x[] = {200,300,400,400,300,240,160,160,200,210};
int y[] = {100, 80,100,220,320,320,240,200,160,150};
void main()
{
int old_mode;
old_mode = fg_getmode();
if (fg_testmode(16,1))
fg_setmode(16);
else if (fg_testmode(15,1))
fg_setmode(15);
else {
printf("This program requires a 640 x 350 ");
printf("EGA graphics mode.\n");
exit(1);
}
fg_setcolor(1);
fg_polygon(x,y,VERTICES);
fg_waitkey();
fg_setmode(old_mode);
fg_reset();
}
Chapter 6: Graphics Fundamentals 107
As shown in this example, the fg_polygon routine expects the x and y
components defining the polygon vertices to be in separate arrays. Another
routine, fg_polyline, draws an unfilled polygon from polygon vertices in one
integer array. With fg_polyline, the first array element is the x component
of the first vertex, the second element is the y component of the first
vertex, the third element is the x component of the second vertex, and so
forth. The first fg_polyline argument is the vertex coordinate array of
alternating x and y components, and the second argument specifies the number
of vertices. In other respects, fg_polyline is identical to fg_polygon.
An additional feature available with fg_polyline but not fg_polygon is
the ability to specify vertex offsets. The fg_polyoff routine's two integer
arguments respectively define offset values that are added to each
fg_polyline vertex. This makes it possible to define polygon vertices as
relative values, that when combined with the offsets, determine the polygon's
absolute position.
Perhaps the most important polygon display routine is fg_polyfill, which
displays a filled convex polygon in screen space (the polygon is filled with
pixels of the current color). Its first argument is a vertex array in the
same format used by fg_polyline. The next argument is a work array used
internally. The size of the work array must be at least twice the polygon
height if defined as an integer array, or four times the polygon height if
defined as a byte array. The final argument specifies the number of polygon
vertices.
Example 6-8 illustrates the use of the fg_polyline, fg_polyoff, and
fg_polyfill routines. The program first draws an unfilled polygon, centered
within the left half of the screen. It then draws a filled version of the
same polygon, centered within the right half of the screen. In each case,
the centering is accomplished by passing appropriate values to fg_polyoff.
After waiting for a keystroke, the program establishes a clipping region in
the lower right corner and redraws the filled polygon at the same position
but in a different color. This of course results in only a portion of the
filled polygon being drawn. Like example 6-7, this example requires a 640 by
350 graphics mode.
Example 6-8.
#include <fastgraf.h>
#include <stdio.h>
#include <stdlib.h>
void main(void);
#define VERTICES 10
int xy[] = {200,100, 300, 80, 400,100, 400,220, 300,320,
240,320, 160,240, 160,200, 200,160, 210,150};
int work_array[700];
void main()
{
int old_mode;
old_mode = fg_getmode();
if (fg_testmode(16,1))
fg_setmode(16);
108 Fastgraph User's Guide
else if (fg_testmode(15,1))
fg_setmode(15);
else {
printf("This program requires a 640 x 350 ");
printf("EGA graphics mode.\n");
exit(1);
}
fg_setcolor(1);
fg_polyoff(-120,-25);
fg_polyline(xy,VERTICES);
fg_polyoff(200,-25);
fg_polyfill(xy,work_array,VERTICES);
fg_waitkey();
fg_setcolor(2);
fg_setclip(480,639,175,349);
fg_polyfill(xy,work_array,VERTICES);
fg_waitkey();
fg_setmode(old_mode);
fg_reset();
}
The fg_polyfill routine fills convex polygons. From Fastgraph's
perspective, a polygon is convex if any horizontal line drawn through the
polygon crosses the left edge exactly once and the right edge exactly once
(excluding horizontal and zero-length edge segments). Note that this
definition includes shapes that are not convex in the traditional sense. In
addition, any non-convex polygon can be decomposed into two or more convex
polygons.
The filled convex polygon is a fundamental tool of three-dimensional
computer graphics. A common practice is to build an image or object from
several adjacent or connecting polygons. Such polygons typically overlap at
one or more edges. For instance, the coordinates defining the right edge of
one polygon may also define the left edge of another polygon immediately to
its right. For an overall image to appear correct, its component polygons
must fit together correctly. The fg_polyfill routine applies the following
rules to handle overlapping polygon edges:
Points located exactly on non-horizontal edges are drawn
only if the polygon's interior is directly to the right.
Points located exactly on horizontal edges are drawn only
if the polygon's interior is directly below them.
A vertex is drawn only if all lines ending at that point
meet the above two conditions.
These three rules ensure that no pixel is drawn more than once when filling
adjacent polygons. However, they may not be suitable for displaying polygons
that are not adjacent because some of the pixels on the polygon's edge will
not be included. If this is an issue, first draw the filled polygon with
fg_polyfill, then draw an unfilled polygon having the same vertices with
fg_polyline.
Chapter 6: Graphics Fundamentals 109
The final Fastgraph routine relating to polygons is fg_inside, which
checks if a specified point lies inside a convex polygon. Its first argument
is a vertex array in the same format used by fg_polyline and fg_polyfill.
The second argument is the number of vertices in the polygon, while the last
two arguments specify the screen space x and y coordinates of the point being
tested. The fg_inside function returns 1 if the point lies inside the
polygon and 0 if not. If the vertex array does not define a convex polygon,
the return value is undefined.
Circles and Ellipses
Fastgraph includes routines for drawing filled and unfilled circles and
ellipses. Both screen space and world space versions of these routines are
available, and all of them observe the clipping limits.
The fg_circle routine draws an unfilled circle in screen space, centered
at the graphics cursor position, using the current color. The routine's only
argument specifies the circle's radius in horizontal screen space units.
Another routine, fg_circlew, draws an unfilled circle where the radius is
measured in horizontal world space units. The analogous routines for drawing
filled circles are fg_circlef and fg_circlefw. All four circle drawing
routines leave the graphics cursor position unchanged.
The fg_ellipse routine draws an unfilled ellipse in screen space,
centered at the graphics cursor position, using the current color. The
routine requires two arguments that respectively specify the length of its
horizontal and vertical semi-axes. In other words, the first argument is the
absolute distance from the center of the ellipse to its horizontal extremity,
and the second argument is the absolute distance from the center to the
vertical extremity. Another routine, fg_ellipsew, draws an unfilled ellipse
in world space. The analogous routines for drawing filled ellipses are
fg_ellipsef and fg_ellipsfw. All four ellipse drawing routines leave the
graphics cursor position unchanged.
Example 6-9 illustrates the use of the fg_circlew and fg_ellipsew
routines. The program first uses the fg_automode routine to propose a
graphics video mode and then uses the fg_setmode routine to select that video
mode. It then makes color 15 the current color, which by default is white in
all color graphics modes and "on" in the monochrome graphics modes. Next, it
establishes a 200-unit by 200-unit world space coordinate system. The
program then uses fg_ellipsew to draw an ellipse and fg_circlew to draw a
circle, both centered at the middle of the screen (which is the origin of our
world space coordinate system). The circle has a radius of 1/16 the width of
the screen (12.5 horizontal world space units), and the ellipse is
horizontally inscribed within the circle.
Example 6-10 illustrates the use of the fg_circle and fg_ellipse
routines. It is functionally identical to example 6-9, but it uses screen
space rather than world space coordinates to draw the circle and ellipse.
Note the arguments to the fg_circle and fg_ellipse routines are dependent on
the maximum x and y coordinates of the selected video mode. If we didn't
compute these arguments in this manner, the actual size of the circle and
ellipse would be proportional to the pixel resolution of the video mode. No
such dependency exists when using world space, but we pay a price for this
feature in slightly slower execution speed.
110 Fastgraph User's Guide
Example 6-9. Example 6-10.
#include <fastgraf.h> #include <fastgraf.h>
void main(void); void main(void);
void main() void main()
{ {
int old_mode; int mid_x, mid_y;
int old_mode;
old_mode = fg_getmode(); int x,y;
fg_setmode(fg_automode());
fg_setcolor(15); old_mode = fg_getmode();
fg_setmode(fg_automode());
fg_initw(); fg_setcolor(15);
fg_setworld(-100.0,100.0,-100.0,100.0);
mid_x = fg_getmaxx() / 2;
fg_movew(0.0,0.0); mid_y = fg_getmaxy() / 2;
fg_ellipsew(12.5,12.5); x = mid_x / 8;
fg_circlew(12.5); y = mid_y / 8;
fg_waitkey();
fg_move(mid_x,mid_y);
fg_setmode(old_mode); fg_ellipse(x,y);
fg_reset(); fg_circle(x);
} fg_waitkey();
fg_setmode(old_mode);
fg_reset();
}
Chapter 6: Graphics Fundamentals 111
Solid Rectangles
Fastgraph includes four routines for drawing solid rectangles, two for
screen space and two for world space, with and without clipping. None of
these routines affect the graphics cursor position.
The fg_rect routine draws a solid rectangle in screen space, without
regard to the clipping limits, using the current color. Fg_rect requires
four integer arguments that respectively define the minimum x, maximum x,
minimum y, and maximum y screen space coordinates of the rectangle. The
minimum coordinates must be less than or equal to the maximum coordinates, or
else the results are unpredictable. The fg_clprect routine is identical in
all respects to the fg_rect routine, except it observes the clipping limits.
The world space versions of the solid rectangle drawing routines are
fg_rectw and fg_clprectw. Like fg_rect and fg_clprect, they require four
arguments that define the extremes of the rectangle, but the arguments are
floating point world space coordinates.
You also can use fg_rect in text modes. When used in a text mode,
fg_rect expects its four arguments to be expressed in character space (that
is, rows and columns) rather than screen space. This means the four
arguments respectively specify the minimum column, maximum column, minimum
row, and maximum row of the rectangle. Fastgraph constructs the rectangle by
storing the solid block character (ASCII decimal value 219) in each character
cell comprising the rectangle. The rectangle is drawn using the current
character attribute, but because the solid block character occupies the
entire character cell, the background component of the attribute is
essentially meaningless.
Example 6-11 demonstrates the use of the fg_rect routine by drawing 200
random-size rectangles in random colors. The program first uses the
fg_automode routine to propose a graphics video mode and then uses the
fg_setmode routine to select that video mode. Next, it determines the
horizontal and vertical screen resolution for the selected video mode, using
the fg_getmaxx and fg_getmaxy routines. The main part of the program is a
for loop that generates a random rectangle in each iteration. Inside the
loop, the C library function rand is used to generate the extremes of the
rectangle. If necessary, the program then exchanges the coordinates to make
the minimum coordinates less than or equal to the maximum coordinates.
Finally, it again uses rand to generate a random color number between 0 and
15, and then draws the rectangle in that color. After drawing all 200
rectangles, the program restores the original video mode and screen
attributes before returning to DOS.
Example 6-11.
#include <fastgraf.h>
void main(void);
#define RECTANGLES 200
#define SWAP(a,b,temp) { temp = a; a = b; b = temp; }
112 Fastgraph User's Guide
void main()
{
int i;
int minx, maxx, miny, maxy;
int old_mode;
int temp;
int xres, yres;
old_mode = fg_getmode();
fg_setmode(fg_automode());
xres = fg_getmaxx() + 1;
yres = fg_getmaxy() + 1;
for (i = 0; i < RECTANGLES; i++) {
minx = rand() % xres;
maxx = rand() % xres;
miny = rand() % yres;
maxy = rand() % yres;
if (minx > maxx)
SWAP(minx,maxx,temp);
if (miny > maxy)
SWAP(miny,maxy,temp);
fg_setcolor(rand()%16);
fg_rect(minx,maxx,miny,maxy);
}
fg_setmode(old_mode);
fg_reset();
}
Unfilled Rectangles
Fastgraph includes a routine for drawing unfilled rectangles. The
fg_box routine draws an unfilled rectangle in screen space, with regard to
the clipping limits, using the current color. The arguments to fg_box are
the same as those for fg_rect. The depth of the rectangle's edges is one
pixel by default, but you can change the depth by calling fg_boxdepth. The
fg_boxdepth routine expects two arguments. The first argument is the width
of the rectangle's left and right sides, while the second is the height of
its top and bottom sides. Once you call fg_boxdepth, fg_box draws all
unfilled rectangles using the depth values specified in the most recent call
to fg_boxdepth. Unlike fg_rect, the fg_box routine has no effect in text
video modes. The analogous world space routine is fg_boxw.
Example 6-12 is the same as example 6-11, but it draws unfilled instead
of solid rectangles. The program uses fg_box to draw the each rectangle and
fg_boxdepth to define the rectangle depth at three pixels in each direction.
Note that you don't need to call fg_boxdepth for each rectangle if you want
all of them to have the same depth.
Example 6-12.
#include <fastgraf.h>
void main(void);
Chapter 6: Graphics Fundamentals 113
#define RECTANGLES 200
#define SWAP(a,b,temp) { temp = a; a = b; b = temp; }
void main()
{
int i;
int minx, maxx, miny, maxy;
int old_mode;
int temp;
int xres, yres;
old_mode = fg_getmode();
fg_setmode(fg_automode());
fg_boxdepth(3,3);
xres = fg_getmaxx() + 1;
yres = fg_getmaxy() + 1;
for (i = 0; i < RECTANGLES; i++) {
minx = rand() % xres;
maxx = rand() % xres;
miny = rand() % yres;
maxy = rand() % yres;
if (minx > maxx)
SWAP(minx,maxx,temp);
if (miny > maxy)
SWAP(miny,maxy,temp);
fg_setcolor(rand()%16);
fg_box(minx,maxx,miny,maxy);
}
fg_setmode(old_mode);
fg_reset();
}
The fg_boxx and fg_boxxw routines are screen space and world space
"exclusive or" versions of the box drawing routines. They simplify
displaying rubberband boxes (hollow rectangles that move in response to
keystrokes or mouse movement) because drawing an object in XOR mode makes it
appear, but drawing it again in the same position and in the same color
restores what was under the object originally. Given this useful property,
here is an outline of what's necessary to draw a rubberband box:
1. Draw the box in its initial position with fg_boxx or
fg_boxxw.
2. Wait for a user response that signifies box movement.
3. Use fg_boxx or fg_boxxw to redraw the box in the same
position as in step 1. This restores what was there
originally.
4. Draw the box in its new position with fg_boxx or
fg_boxxw.
5. Repeat steps 2, 3, and 4 until the box is no longer
needed.
114 Fastgraph User's Guide
Example 6-13 shows a simple use of fg_boxx in the 320 by 200 MCGA/VGA
256-color mode (mode 19). The program fills the left and right halves of the
screen with different colors and then displays an XOR box the overlaps each
half. Even though the box is drawn in the same color as the right half, it
is still visible because drawing something in an XOR mode (except in color 0)
guarantees that it will be visible against its background. After a
keystroke, the program redraws the same box, which of course restores what
was there in the first place.
Example 6-13.
#include <fastgraf.h>
void main(void);
void main()
{
int old_mode;
old_mode = fg_getmode();
fg_setmode(19);
fg_setcolor(9);
fg_rect(0,159,0,199);
fg_setcolor(15);
fg_rect(160,319,0,199);
fg_waitkey();
fg_boxx(80,239,50,149);
fg_waitkey();
fg_boxx(80,239,50,149);
fg_waitkey();
fg_setmode(old_mode);
fg_reset();
}
Dithered Rectangles
The process of alternating different color pixels across a region of the
display area is called dithering. This technique is especially useful in the
graphics modes with few colors, such as CGA and Hercules modes, because you
can simulate additional colors through effective uses of dithering.
Fastgraph includes two routines for drawing dithered rectangles, one for
screen space and one for world space. Neither routine observes the clipping
limits, nor do they affect the graphics cursor position.
The fg_drect routine draws a dithered rectangle in screen space. Like
the fg_rect routine, fg_drect requires four integer arguments that
respectively define the minimum x, maximum x, minimum y, and maximum y screen
space coordinates of the rectangle. The minimum coordinates must be less
than or equal to the maximum coordinates, or else the results are
unpredictable. However, fg_drect also requires a fifth argument that defines
the dithering matrix, which in turn determines the pixel pattern used to
build the dithered rectangle. The size and format of the dithering matrix
are dependent on the video mode.
Chapter 6: Graphics Fundamentals 115
The world space version of the dithered rectangle drawing routine is
fg_drectw. Like fg_drect, it requires four arguments that define the
extremes of the rectangle, and a fifth argument that defines the dithering
matrix.
As mentioned earlier, the size and format of the dithering matrix are
dependent on the video mode. The dithering matrix is a four byte array in
all video modes except the 256 color graphics modes (modes 19 through 27),
where it is an eight byte array. This array contains a pixel pattern that
fg_drect or fg_drectw replicates across the rectangle's area. The structure
of the dithering matrix closely mimics the structure of video memory in each
graphics mode.
The remainder of this section will present some simple mode-specific
examples to illustrate the structure of the dithering matrix in the different
graphics modes. Suppose we would like to produce a "checkerboard" of light
blue and white pixels. That is, in a given row of a rectangle, consecutive
pixels will alternate between these two colors. Additionally, the pattern
for adjacent rows will be shifted such that there will always be a white
pixel above and below a light blue pixel, and vice versa. Hence this pixel
pattern would look something like
B W B W
W B W B
B W B W
W B W B
where each B represents a light blue pixel, and each W represents a white
pixel. The following examples describe the dithering matrix that could be
used to produce such a pixel pattern in each graphics mode.
CGA Four-Color Graphics Modes
The CGA four-color graphics modes (modes 4 and 5) use a four-byte
dithering matrix that Fastgraph treats as a four-row by one-column array.
Since each pixel in these modes requires two bits of video memory, each byte
of the dithering matrix holds four pixels. Thus, the pixel representation of
the dithering matrix would appear as shown below on the left; its translation
to numeric values appears on the right.
[3] B W B W [3] 01 11 01 11
[2] W B W B [2] 11 01 11 01
[1] B W B W [1] 01 11 01 11
[0] W B W B [0] 11 01 11 01
Because these modes do not offer a light blue color, we've used light cyan
(color value 1 in palette 1) to approximate light blue. The B pixels thus
translate to color value 1, or 01 binary. White is available as color value
3 in palette 1, so the W pixels translate to color value 3, or 11 binary.
The hexadecimal equivalent of the binary value 11011101 (for array elements
[0] and [2]) is DD, and the hexadecimal equivalent of the binary value
01110111 (for array elements [1] and [3]) is 77. As shown in example 6-12,
116 Fastgraph User's Guide
these are precisely the values assigned to the elements of the dithering
matrix.
Example 6-14 uses mode 4 to display a 50-pixel by 50-pixel dithered
rectangle in the upper left corner of the screen. The dithering matrix
represents the blue and white checkerboard pattern discussed in the preceding
paragraph.
Example 6-14.
#include <fastgraf.h>
void main(void);
void main()
{
char matrix[4];
int old_mode;
old_mode = fg_getmode();
fg_setmode(4);
matrix[0] = matrix[2] = 0xDD;
matrix[1] = matrix[3] = 0x77;
fg_drect(0,49,0,49,matrix);
fg_waitkey();
fg_setmode(old_mode);
fg_reset();
}
CGA Two-Color Graphics Mode
The CGA two-color graphics mode (mode 6) uses a four-byte dithering
matrix that Fastgraph treats as a four-row by one-column array, as in the
other four-color CGA modes. However, each pixel in this mode only requires
one bit of video memory, so each byte of the dithering matrix holds eight
pixels. Thus, the pixel representation of the dithering matrix would appear
as shown below on the left; its translation to numeric values appears on the
right.
[3] B W B W B W B W [3] 0 1 0 1 0 1 0 1
[2] W B W B W B W B [2] 1 0 1 0 1 0 1 0
[1] B W B W B W B W [1] 0 1 0 1 0 1 0 1
[0] W B W B W B W B [0] 1 0 1 0 1 0 1 0
Mode 6 obviously does not offer a light blue color, so we've used black
(color value 0) in its place. The B pixels thus translate to color value 0.
White is available as color value 1, so the W pixels translate to color value
1. The hexadecimal equivalent of the binary value 10101010 (for array
elements [0] and [2]) is AA, and the hexadecimal equivalent of the binary
value 01010101 (for array elements [1] and [3]) is 55. Thus, to make example
Chapter 6: Graphics Fundamentals 117
6-14 run in mode 6, we only need to change the fg_setmode argument from 4 to
6 and change the dithering matrix values as shown below.
matrix[0] = matrix[2] = 0xAA;
matrix[1] = matrix[3] = 0x55;
Tandy/PCjr 16-Color Graphics Mode
The Tandy/PCjr 16-color graphics mode (mode 9) also uses a four-byte
dithering matrix that Fastgraph treats as a four-row by one-column array.
Each pixel in this mode requires four bits of video memory, so each byte of
the dithering matrix only holds two pixels. Thus, the pixel representation
of the dithering matrix would appear as shown below on the left; its
translation to numeric values appears on the right.
[3] B W [3] 1001 1111
[2] W B [2] 1111 1001
[1] B W [1] 1001 1111
[0] W B [0] 1111 1001
The B pixels translate to color value 9 (light blue), or 1001 binary, and the
W pixels translate to color value 15 (white), or 1111 binary. The
hexadecimal equivalent of the binary value 11111001 (for array elements [0]
and [2]) is F9, and the hexadecimal equivalent of the binary value 10011111
(for array elements [1] and [3]) is 9F. Thus, to make example 6-14 run in
mode 9, we only need to change the fg_setmode argument from 4 to 9 and change
the dithering matrix values as shown below.
matrix[0] = matrix[2] = 0xF9;
matrix[1] = matrix[3] = 0x9F;
Hercules Graphics Mode
The size and format of the dithering matrix in the Hercules graphics
mode (mode 11) are the same as in the CGA two-color mode (mode 6).
Hercules Low-Resolution Graphics Mode
The size and format of the dithering matrix in the Hercules low-
resolution graphics mode (mode 12) are the same as in the CGA four-color
modes (modes 4 and 5). As far as our checkerboard example goes, we'll use
black (color value 0) in place of light blue, and bold (color value 3)
instead of white. Thus, the B pixels translate to 00 binary, while the W
pixels translate to 11 binary. The hexadecimal equivalent of the binary
value 11001100 (for array elements [0] and [2]) is CC, and the hexadecimal
equivalent of the binary value 00110011 (for array elements [1] and [3]) is
33. Thus, to make example 6-14 run in mode 12, we only need to change the
118 Fastgraph User's Guide
fg_setmode argument from 4 to 12 and change the dithering matrix values as
shown below.
matrix[0] = matrix[2] = 0xCC;
matrix[1] = matrix[3] = 0x33;
EGA/VGA/SVGA 16-Color Graphics Modes
The EGA/VGA/SVGA 16-color graphics modes (modes 13 through 18, 28, and
29) use a four-byte dithering matrix that Fastgraph treats as a four-row by
one-column array. Unlike the other graphics modes, which allow you to store
pixels of several colors in the dithering matrix, these modes treat the
dithering matrix as a bit map for a specific color. Since each color in the
dither pattern must be stored in a separate bit map (that is, in a separate
dithering matrix), you must call fg_drect once for each color. Furthermore,
you must use the fg_setcolor routine before each call to fg_drect to define
the color used with the dithering matrix.
In all EGA/VGA/SVGA graphics modes, each byte of the dithering matrix is
a bit map that represents eight pixels. Using our familiar checkerboard
example, the pixel representation of the dithering matrix would appear as
shown below.
[3] B W B W B W B W
[2] W B W B W B W B
[1] B W B W B W B W
[0] W B W B W B W B
Translating this pattern to numeric values is simple. Just construct one
dithering matrix for each color in the pattern (there are two colors in this
example), where pixels of the current color translate to 1, and other pixels
translate to 0. Following our example, the translation for the B pixels
appears below on the left, while the translation for the W pixels appears on
the right.
[3] 1 0 1 0 1 0 1 0 [3] 0 1 0 1 0 1 0 1
[2] 0 1 0 1 0 1 0 1 [2] 1 0 1 0 1 0 1 0
[1] 1 0 1 0 1 0 1 0 [1] 0 1 0 1 0 1 0 1
[0] 0 1 0 1 0 1 0 1 [0] 1 0 1 0 1 0 1 0
The hexadecimal equivalent of the binary value 01010101 is 55, and the
hexadecimal equivalent of the binary value 10101010 is AA. As shown in
example 6-15, these are precisely the values assigned to the elements of the
dithering matrices.
Chapter 6: Graphics Fundamentals 119
Example 6-15 uses mode 13 to display our light blue and white
checkerboard pattern. Note you must call fg_drect twice -- once for the
light blue pixels (color value 9), and again for the white pixels (color
value 15). Note also how fg_setcolor is used before each call to fg_drect to
define the color of the pixels fg_drect will display.
Example 6-15.
#include <fastgraf.h>
void main(void);
void main()
{
char matrix[4];
int old_mode;
old_mode = fg_getmode();
fg_setmode(13);
matrix[0] = matrix[2] = 0x55;
matrix[1] = matrix[3] = 0xAA;
fg_setcolor(9);
fg_drect(0,49,0,49,matrix);
matrix[0] = matrix[2] = 0xAA;
matrix[1] = matrix[3] = 0x55;
fg_setcolor(15);
fg_drect(0,49,0,49,matrix);
fg_waitkey();
fg_setmode(old_mode);
fg_reset();
}
256-Color Graphics Modes
The 256-color graphics modes (modes 19 through 27) use an eight-byte
dithering matrix that Fastgraph treats as a four-row by two-column array.
Each pixel in these modes requires eight bits of video memory, so each byte
of the dithering matrix only holds a single pixel. We therefore need the two
column dithering matrix to produce a meaningful dither pattern. The pixel
representation of the dithering matrix would appear as shown below on the
left; its translation to numeric values appears on the right.
[6] B W [7] [6] 9 15 [7]
[4] W B [5] [4] 15 9 [5]
[2] B W [3] [2] 9 15 [3]
[0] W B [1] [0] 15 9 [1]
120 Fastgraph User's Guide
The B pixels translate to color value 9 (light blue), and the W pixels
translate to color value 15 (white). Example 6-16 uses mode 19 to draw our
light blue and white checkerboard pattern.
Example 6-16.
#include <fastgraf.h>
void main(void);
void main()
{
char matrix[8];
int old_mode;
old_mode = fg_getmode();
fg_setmode(19);
matrix[0] = matrix[3] = matrix[4] = matrix[7] = 15;
matrix[1] = matrix[2] = matrix[5] = matrix[6] = 9;
fg_drect(0,49,0,49,matrix);
fg_waitkey();
fg_setmode(old_mode);
fg_reset();
}
Closing Remarks
There are two other important items pertaining to the fg_drect and
fg_drectw routines. These items apply regardless of which graphics video
mode is being used.
First, the dithering matrix may not contain virtual color values. That
is, the pixel color values stored in the dithering matrix must be between 0
and the maximum color value for the current video mode. If any color value
is redefined using the fg_defcolor routine, Fastgraph always ignores the
redefinition and instead uses the actual color value. Note this does not
apply to palette registers or video DAC registers, because in these cases we
are redefining the color associated with a color value and not the color
value itself.
Second, Fastgraph aligns the dithering matrix to specific pixel rows.
Fastgraph draws the dithered rectangle starting with the pixel row specified
by the rectangle's lower limit (the maximum y coordinate for fg_drect, or the
minimum y coordinate for fg_drectw) and proceeds upward until reaching the
rectangle's upper limit. In all cases the dithering matrix used by fg_drect
and fg_drectw contains four rows. If we let r represent the pixel row
corresponding to the rectangle's lower limit, then the first row used in the
dithering matrix is r modulo 4 (assuming the dithering matrix rows are
numbered 0 to 3). This alignment enables you to use the same dithering
matrix in multiple calls to fg_drect and fg_drectw for building an object of
adjacent dithered rectangles (for example, an L-shaped area) and still have
the dither pattern match where the rectangles intersect.
Chapter 6: Graphics Fundamentals 121
Region Fill
Fastgraph includes routines for filling arbitrary regions. The fg_flood
and fg_paint routines fill a region with the current color value by
specifying a screen space point in the region's interior. The fg_floodw and
fg_paintw routine also fill a region, but they require the interior point to
be expressed in world space. All region fill routines have two arguments
that specify the (x,y) coordinates of the interior point. For fg_flood and
fg_paint, the arguments are integer quantities. For fg_floodw and fg_paintw,
they are floating point quantities. None of them change the graphics cursor
position. The difference between the "flood" and "paint" versions of these
routines is simple: fg_flood and fg_floodw will not extend the region fill
beyond the clipping limits, while fg_paint and fg_paintw ignore the clipping
limits. As a result, fg_paint and fg_paintw are significantly faster.
The region being filled must be a closed polygon whose boundary color is
different from that of the specified interior point. The region may contain
holes (interior areas that will not be filled). Fastgraph fills the region
by changing every interior pixel whose color is the same as the specified
interior point, to the current color. If the interior point is already the
current color, the region fill routines do nothing. It is important to note
fg_paint and fg_paintw do not treat the screen edges as polygon boundaries.
Filling an open polygon will cause these routines to behave unpredictably.
This is not the case with fg_flood and fg_floodw as long as the clipping
limits are not beyond the screen edges.
Example 6-17 illustrates a simple use of the fg_paint routine in a 320
by 200 graphics mode. The program uses fg_bestmode to select an available
video mode (if no 320 by 200 graphics mode is available, the program exits).
After establishing the selected video mode, the program uses fg_move and
fg_drawrel to draw a hollow rectangle in color 10 and a hollow diamond in
color 9. The diamond is drawn in the middle of the rectangle, thus making it
a hole with respect to the rectangle. The program leaves these shapes on the
screen until a key is pressed. At that time, it calls fg_paint to fill that
part of the rectangle outside the diamond with color 10. After waiting for
another keystroke, the program again uses fg_paint to fill the interior of
the diamond with color 15. Finally, the program waits for another keystroke,
restores the original video mode and screen attributes, and returns to DOS.
Example 6-17.
#include <fastgraf.h>
#include <stdio.h>
#include <stdlib.h>
void main(void);
void main()
{
int old_mode, new_mode;
new_mode = fg_bestmode(320,200,1);
if (new_mode < 0) {
printf("This program requires a 320 x 200 ");
printf("graphics mode.\n");
exit(1);
}
122 Fastgraph User's Guide
old_mode = fg_getmode();
fg_setmode(new_mode);
fg_setcolor(10);
fg_move(100,50);
fg_drawrel(120,0);
fg_drawrel(0,100);
fg_drawrel(-120,0);
fg_drawrel(0,-100);
fg_setcolor(9);
fg_move(160,80);
fg_drawrel(30,20);
fg_drawrel(-30,20);
fg_drawrel(-30,-20);
fg_drawrel(30,-20);
fg_waitkey();
fg_setcolor(10);
fg_paint(160,70);
fg_waitkey();
fg_setcolor(15);
fg_paint(160,100);
fg_waitkey();
fg_setmode(old_mode);
fg_reset();
}
Summary of Fundamental Graphics 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_BOX draws an unfilled rectangle in screen space, with respect to the
clipping region. The width of the rectangle's edges is one pixel unless
changed with the fg_boxdepth routine.
FG_BOXDEPTH defines the depth of rectangles drawn with the box display
routines. The fg_setmode routine initializes the box depth to one pixel.
FG_BOXW draws an unfilled rectangle in world space, with respect to the
clipping region. The width of the rectangle's edges is one pixel unless
changed with the fg_boxdepth routine.
FG_BOXX draws an unfilled rectangle in screen space, with respect to the
clipping region, in "exclusive or" mode. The width of the rectangle's edges
is one pixel unless changed with the fg_boxdepth routine.
Chapter 6: Graphics Fundamentals 123
FG_BOXXW draws an unfilled rectangle in world space, with respect to the
clipping region, in "exclusive or" mode. The width of the rectangle's edges
is one pixel unless changed with the fg_boxdepth routine.
FG_CIRCLE draws an unfilled circle in screen space. The circle is
centered at the graphics cursor position.
FG_CIRCLEF draws a filled circle in screen space. The circle is
centered at the graphics cursor position.
FG_CIRCLEFW draws a filled circle in world space. The circle is
centered at the graphics cursor position.
FG_CIRCLEW draws an unfilled circle in world space. The circle is
centered at the graphics cursor position.
FG_CLPRECT draws a solid (filled) rectangle in screen space, with
respect to the clipping region.
FG_CLPRECTW draws a solid (filled) rectangle in world space, with
respect to the clipping region.
FG_DASH draws a dashed line from the graphics cursor position to an
absolute screen space position. It also makes the destination position the
new graphics cursor position.
FG_DASHREL draws a dashed line from the graphics cursor position to a
screen space position relative to it. It also makes the destination position
the new graphics cursor position.
FG_DASHRW draws a dashed line from the graphics cursor position to a
world space position relative to it. It also makes the destination position
the new graphics cursor position.
FG_DASHW draws a dashed line from the graphics cursor position to an
absolute world space position. It also makes the destination position the
new graphics cursor position.
FG_DRAW draws a solid line from the graphics cursor position to an
absolute screen space position. It also makes the destination position the
new graphics cursor position.
FG_DRAWREL draws a solid line from the graphics cursor position to a
screen space position relative to it. It also makes the destination position
the new graphics cursor position.
FG_DRAWRELX draws a solid line in "exclusive or" mode from the graphics
cursor position to a screen space position relative to it. It also makes the
destination position the new graphics cursor position.
FG_DRAWRW draws a solid line from the graphics cursor position to a
world space position relative to it. It also makes the destination position
the new graphics cursor position.
FG_DRAWRXW draws a solid line in "exclusive or" mode from the graphics
cursor position to a world space position relative to it. It also makes the
destination position the new graphics cursor position.
124 Fastgraph User's Guide
FG_DRAWW draws a solid line from the graphics cursor position to an
absolute world space position. It also makes the destination position the
new graphics cursor position.
FG_DRAWX draws a solid line in "exclusive or" mode from the graphics
cursor position to an absolute screen space position. It also makes the
destination position the new graphics cursor position.
FG_DRAWXW draws a solid line in "exclusive or" mode from the graphics
cursor position to an absolute world space position. It also makes the
destination position the new graphics cursor position.
FG_DRECT draws a dithered rectangle in screen space, without regard to
the clipping region. The rectangle's dither pattern is defined through a
dithering matrix whose format is dependent on the video mode being used.
FG_DRECTW draws a dithered rectangle in world space, without regard to
the clipping region. The rectangle's dither pattern is defined through a
dithering matrix whose format is dependent on the video mode being used.
FG_ELLIPSE draws an unfilled ellipse in screen space. The ellipse is
centered at the graphics cursor position, and its size is determined by the
specified lengths of the semi-axes.
FG_ELLIPSEF draws a filled ellipse in screen space. The ellipse is
centered at the graphics cursor position, and its size is determined by the
specified lengths of the semi-axes.
FG_ELLIPSEW draws an unfilled ellipse in world space. The ellipse is
centered at the graphics cursor position, and its size is determined by the
specified lengths of the semi-axes.
FG_ELLIPSFW draws a filled ellipse in world space. The ellipse is
centered at the graphics cursor position, and its size is determined by the
specified lengths of the semi-axes.
FG_ERASE clears the screen in either text or graphics modes.
FG_FILLPAGE fills the screen with the current color in either text or
graphics modes.
FG_FLOOD fills an arbitrary closed region with the current color value,
with respect to the clipping limits. The region is defined by specifying a
screen space point within its interior.
FG_FLOODW fills an arbitrary closed region with the current color value,
with respect to the clipping limits. The region is defined by specifying a
world space point within its interior.
FG_GETPIXEL returns the color value of a specified pixel.
FG_GETXPOS returns the screen space x coordinate of the graphics cursor
position.
FG_GETYPOS returns the screen space y coordinate of the graphics cursor
position.
Chapter 6: Graphics Fundamentals 125
FG_INSIDE determines if the specified point is inside a given convex
polygon.
FG_MOVE establishes the graphics cursor position at an absolute screen
space point.
FG_MOVEREL establishes the graphics cursor position at a screen space
point relative to the current position.
FG_MOVERW establishes the graphics cursor position at a world space
point relative to the current position.
FG_MOVEW establishes the graphics cursor position at an absolute world
space point.
FG_PAINT fills an arbitrary closed region with the current color value,
without respect to the clipping limits. The region is defined by specifying
a screen space point within its interior.
FG_PAINTW fills an arbitrary closed region with the current color value,
without respect to the clipping limits. The region is defined by specifying
a world space point within its interior.
FG_POINT draws a point (that is, displays a pixel) in screen space.
FG_POINTW draws a point in world space.
FG_POINTX draws a point in "exclusive or" mode in screen space.
FG_POINTXW draws a point in "exclusive or" mode in world space.
FG_POLYFILL draws a filled convex polygon in screen space. The polygon
is closed if necessary.
FG_POLYGON draws an unfilled polygon in screen space, using two
coordinate arrays to define the polygon vertices. The polygon is closed if
necessary.
FG_POLYGONW draws an unfilled polygon in world space. It is the same as
the fg_polygon routine, except the coordinate arrays contain world space
values.
FG_POLYLINE draws an unfilled polygon in screen space, using a single
coordinate array to define the polygon vertices. The polygon is closed if
necessary.
FG_POLYOFF defines the screen space offset applied to each vertex for
polygons drawn with fg_polyfill or fg_polyline.
FG_RECT draws a solid (filled) rectangle in screen space or character
space, without regard to the clipping region.
FG_RECTW draws a solid (filled) rectangle in world space, without regard
to the clipping region.
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FG_SETCLIP defines the clipping region in screen space. The clipping
region is a rectangular area outside of which graphics are suppressed.
FG_SETCLIPW defines the clipping region in world space.
