Inside Macintosh: QuickDraw GX Objects /

Chapter 4 - Colors and Color-Related Objects / Colors and Color-Related Objects Reference

Constants and Data Types

Color Values

Color-component values combine to form color values. Each color value is a complete specification of a single color in a given color space. QuickDraw GX recognizes the following ten fundamental types of color values:

• CMYK color value. It contains color-component values for cyan, magenta, yellow, and black. It is defined by the gxCMYKColor type definition:

   struct gxCMYKColor{
      gxColorValue   cyan;
      gxColorValue   magenta;
      gxColorValue   yellow;
      gxColorValue   black;
   };

• RGB color value. It contains color-component values for red, green, and blue. It is defined by the gxRGBColor type definition:

   struct gxRGBColor{
      gxColorValue   red;
      gxColorValue   green;
      gxColorValue   blue;
   };

• Alpha-channel RGB color value. It contains color-component values for red, green, and blue, plus a fourth (alpha) color-component value representing opacity. It is defined by the gxRGBAColor type definition:

   struct gxRGBAColor{
      gxColorValue   red;
      gxColorValue   green;
      gxColorValue   blue;
      gxColorValue   alpha;
   };

• HSV color value. It contains color-component values for hue, saturation, and value. It is defined by the gxHSVColor type definition:

   struct gxHSVColor{
      gxColorValue   hue;
      gxColorValue   saturation;
      gxColorValue   value;
   };

• HLS color value. It contains color-component values for hue, lightness, and saturation. It is defined by the gxHLSColor type definition:

   struct gxHLSColor{
      gxColorValue   hue;
      gxColorValue   lightness;
      gxColorValue   saturation;
   };

• XYZ color value. It contains color-component values for the X, Y, and Z tristimulus values. It is defined by the gxXYZColor type definition:

   struct gxXYZColor {
      gxColorValue   x;
      gxColorValue   y;
      gxColorValue   z;
   };

• Yxy color value. It contains color-component values for the Y, x, and y chromaticity axes. (Note that the Y component is identified in this color structure as capY.) It is defined by the gxYXYColor type definition:

   struct gxYXYColor {
      gxColorValue   capY;
      gxColorValue   x;
      gxColorValue   y;
   };

• L*u*v* color value. It contains color-component values for the L*, u*, and v* axes. It is defined by the gxLUVColor type definition:

   struct gxLUVColor {
      gxColorValue   l;
      gxColorValue   u;
      gxColorValue   v;
   };

• L*a*b* color value. It contains color-component values for the L*, a*, and b* axes. It is defined by the gxLABColor type definition:

   struct gxLABColor {
      gxColorValue   l;
      gxColorValue   a;
      gxColorValue   b;
   };

• YIQ color value. It contains color-component values for the Y, I, and Q axes. It is defined by the gxYIQColor type definition:

   struct gxYIQColor{
      gxColorValue   y;
      gxColorValue   i;
      gxColorValue   q;
   };

• Grayscale color value. It contains a single color-component value for luminance.
• Alpha-channel grayscale color value, containing a color-component value for luminance, plus a second (alpha) color-component value representing opacity. It is defined by the gxGrayAColor type definition:

   struct gxGrayAColor{
      gxColorValue   gray;
      gxColorValue   alpha;
   };

• Indexed color value. It contains an index value (of type gxColorIndex) and a reference to a color set object. The color is obtained by using the index value as an offset into the color set. Indexed color is defined by the gxIndexedColor type definition:

   typedef long gxColorIndex;

   struct gxIndexedColor{
      gxColorIndex   index;
      gxColorSet     set;
   };