The Devil's Doorknob BBS Capture (1996-2003)

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Chapter 5 The Use of Color 48 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 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 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 white 15 bright 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 Chapter 5: The Use of Color 49 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); 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 be used to define text attributes. The fg_setcolor routine packs the three values passed to fg_setattr into a single argument, as shown below. 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 the fg_setcolor routine. Monochrome 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. 50 Fastgraph User's Guide 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. 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. Some of the graphics modes also have palette registers or video DAC registers to provide additional color capabilities. 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 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 white 15 bright white At this point it is important to 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 zeroed 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. The Fastgraph routine fg_setcolor defines the color in which subsequent graphics operations are performed. This color is called the current color. Chapter 5: The Use of Color 51 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, 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 bright white bright white palette 3 palette 4 palette 5 color 1 green cyan cyan color 2 red magenta red color 3 brown white white 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, the fg_setcolor routine 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 the fg_palette routine 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 the fg_palette and fg_setcolor routines 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. 52 Fastgraph User's Guide Example 5-1. #include <fastgraf.h> void main(void); void main() { int mode; mode = fg_getmode(); fg_setmode(4); fg_palette(0,1); fg_setcolor(3); fg_text("Hello",5); 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 bright white by default, but it can be changed to any of the colors in the standard color set. It should be mentioned that changing the foreground color works on true CGA adapters, but there are very few EGA and VGA adapters that correctly implement changing the foreground color in their mode 6 emulation. In mode 6, the fg_setcolor routine 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). To be consistent with the other graphics modes, the fg_palette routine 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 the fg_palette and fg_setcolor routines 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; mode = fg_getmode(); fg_setmode(6); Chapter 5: The Use of Color 53 fg_palette(0,14); fg_setcolor(1); fg_text("Hello",5); fg_waitkey(); fg_setmode(mode); fg_reset(); } 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, the fg_setcolor routine 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 the fg_palette routine 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. Whereas the fg_palette routine 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 the fg_setrgb routine 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); 54 Fastgraph User's Guide could be used to define palette register 1 as light cyan in mode 9. Example 5-3 demonstrates the use of the fg_palette and fg_setcolor routines 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 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 bright 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; 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 the fg_setcolor routine 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. Chapter 5: The Use of Color 55 Example 5-4. #include <fastgraf.h> void main(void); void main() { int mode; 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 half 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 the fg_setcolor routine 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; mode = fg_getmode(); fg_setmode(12); fg_setcolor(3); fg_text("Hello",5); fg_waitkey(); 56 Fastgraph User's Guide fg_setmode(mode); fg_reset(); } 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, the fg_setcolor routine 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 the fg_palette routine 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 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 white 23 bright white You also can use the Fastgraph routine fg_setrgb to define the color assigned to a specific palette register. Whereas the fg_palette routine 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 the fg_setrgb routine 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 Chapter 5: The Use of Color 57 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, the color light cyan is represented by the color value 19, and it is 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 the fg_palette and fg_setcolor routines 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 bright 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; mode = fg_getmode(); fg_setmode(13); fg_palette(0,1); fg_palette(1,22); fg_setcolor(1); fg_text("Hello",5); fg_waitkey(); 58 Fastgraph User's Guide fg_palette(1,23); fg_waitkey(); fg_setmode(mode); fg_reset(); } 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 numbering scheme might seem rather strange at first, but it 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, the fg_setcolor routine 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 the fg_palette routine 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 the fg_palette and fg_setcolor routines 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; Chapter 5: The Use of Color 59 mode = fg_getmode(); fg_setmode(15); fg_setcolor(4); fg_text("Hello",5); fg_waitkey(); fg_palette(4,8); fg_waitkey(); 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, the fg_setcolor routine 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 the fg_palette routine 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 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 white 63 bright white 60 Fastgraph User's Guide 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. 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 of the 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. Whereas the fg_palette routine 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 the fg_setrgb routine 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 the fg_palette and fg_setcolor routines 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 the fg_palette routine 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. Chapter 5: The Use of Color 61 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; 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 high-resolution 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 62 Fastgraph User's Guide video DAC registers (1 through 15) contain the color value for bright white. This means background pixels (color value 0) are black by default, while foreground pixels (color value 1) are bright 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 bright white. Because the video DAC registers are 18 bits long, each DAC can specify one of 262,144 (218) colors. However, because the palette registers hold 1-bit quantities, only two of these colors can be displayed at 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, the fg_setcolor routine 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, the fg_palette routine specifies the video DAC register that a palette register references. The first argument of the fg_palette routine 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 the fg_setrgb routine 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 the fg_palette, fg_setrgb, and fg_setcolor routines 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, bright 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; mode = fg_getmode(); fg_setmode(17); fg_setrgb(0,0,0,42); fg_setrgb(1,63,63,21); Chapter 5: The Use of Color 63 fg_setcolor(1); fg_text("Hello",5); fg_waitkey(); fg_palette(1,15); fg_waitkey(); fg_setmode(mode); fg_reset(); } VGA 16-Color Mode The VGA high-resolution two-color mode (mode 18) 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. 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 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 white 15 63 63 63 bright white Because the video DAC registers are 18 bits long, each DAC can specify one of 262,144 (218) 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. 64 Fastgraph User's Guide In mode 18, the fg_setcolor, fg_palette, and fg_setrgb routines function exactly as in mode 17 with one exception: there are 16 palette registers instead of just two. Example 5-9 on page 62 demonstrates the use of these routines in mode 17, but it also would work in mode 18 if that video mode number were specified in the call to fg_setmode. VGA and MCGA 256-Color Modes The VGA and MCGA 256-color modes (modes 19 through 23) 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. 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 bright 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, moderateintensity 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 bright white Chapter 5: The Use of Color 65 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 (218) 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 23 provide the capability of displaying 256 simultaneous colors from a group of 262,144. In the VGA and MCGA 256-color video modes, the fg_setcolor routine defines the current color by referencing on of the 256 video DAC registers. The fg_setrgb routine defines the actual color of a video DAC register. The first argument of the fg_setrgb routine 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 23. The first argument of the fg_palette routine 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 the fg_setcolor routine 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 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. Example 5-11. #include<fastgraf.h> #include <fastgraf.h> void main(void); void main(void); #define COLORS 256 void main() { void main() int old_mode; { int red,green, blue; int base; int color; old_mode = fg_getmode(); int mode; fg_setmode(19); 66 Fastgraph User's Guide int x; fg_setcolor(103); mode = fg_getmode(); fg_text("Hello",5); fg_setmode(19); fg_waitfor(18); x = 32; fg_getrgb(103,&red,&green,&blue); for (color=0; color<COLORS; color++) { while(red+green+blue > 0){ fg_setcolor(color); if (red > 0) red--; fg_rect(x,x,0,199); if (green > 0) green--; x++; if (blue > 0) blue--; } fg_setrgb(103,red,green,blue); fg_waitkey(); fg_waitfor(1); } fg_setmode(mode); fg_reset(); fg_setmode(old_mode); } fg_reset(); } Example 5-11 shows an interesting effect available in VGA and MCGA modes. The program uses the Fastgraph routine fg_waitfor (discussed in Chapter 14) 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 the Fastgraph routine 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. 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, using the fg_setdacs and fg_getdacs routines is more efficient. The fg_setdacs routine defines the values of a block of contiguous 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, Chapter 5: The Use of Color 67 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; int old_mode; char RGBvalues[21]; 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 video modes 17 and 18 as long as you just use the first 16 video DAC registers. 68 Fastgraph User's Guide 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 into 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; 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(); fg_setmode(old_mode); fg_reset(); } Chapter 5: The Use of Color 69 Defining All Palette Registers Fastgraph includes a routine fg_palettes that defines all 16 palette registers in modes 9, 13, 14, 16, and 18. You also can use the fg_palettes routine to define the first 16 video DAC registers in modes 19 through 23. It has no effect in other video modes. Using fg_palettes is much faster than calling the fg_palette routine 16 times. The argument to the fg_palettes routine 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; 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 in all graphics modes, even if a particular mode does not have 256 available colors. When you establish a video mode with the fg_setmode routine, 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, the fg_setmode routine initializes color indices 70 Fastgraph User's Guide 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 color 15 is white or bright 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 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. It is important 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. Example 5-15 demonstrates the use of virtual colors in mode 4. After establishing the video mode, the program uses the fg_defcolor routine 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. Chapter 5: The Use of Color 71 Example 5-15. #include <fastgraf.h> void main(void); void main() { int mode; 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 Even though 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> #include <stdio.h> #include <stdlib.h> void main(void); void main() { int mode, old_mode; char string[5]; 72 Fastgraph User's Guide /* Ask for the video mode number */ printf("Which video mode? "); scanf("%d",&mode); /* Make sure the entered value is valid */ if (mode < 0 || mode > 23) { printf("%d is not a valid video mode number.\n",mode); exit(1); } /* Make sure the requested video mode is available */ 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); } /* 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(); Chapter 5: The Use of Color 73 /* 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 the fg_cursor routine to make the cursor invisible. In CGA color modes (modes 4 and 5), the program uses the fg_palette routine 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 the fg_palette routine 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 the fg_defcolor routine to assign the value for normal intensity pixels to color 14. In VGA two-color mode (mode 17), the program uses the fg_palette routine to assign video DAC register 14 to palette register 1. It then defines video DAC register 14 to be yellow with the fg_setrgb routine and finally uses fg_defcolor to assign color 1 (that is, palette register 1) to virtual color 14. In all other video modes, 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_DEFCOLOR assigns a color value to a virtual color index. This routine is only meaningful in the 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 in VGA and MCGA graphics modes. 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 VGA and MCGA graphics modes. 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 the fg_palette routine. This routine is meaningful only in 16-color graphics video modes. 74 Fastgraph User's Guide 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 the 256-color MCGA and VGA 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 Tandy/PCjr, EGA, and VGA graphics modes), or the first 16 video DAC registers (in 256-color MCGA and VGA 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, the fg_setcolor routine 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 VGA and MCGA graphics modes. FG_SETRGB defines the value of a single palette register (in Tandy/PCjr and EGA graphics modes) or video DAC register (in VGA and MCGA 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.