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                         Using Color and Mix Modes
 
You can use the color and mix-mode functions to perform the following
tasks:
 
♦  Create a logical color table.
 
♦  Determine the format and the starting and ending index values of the
   current logical color table.
 
♦  Determine the index value for an entry in the logical color table that is
   the closest match to an RGB value.
 
♦  Determine the RGB value associated with a particular entry in the logical
   color table.
 
♦  Determine and set the current foreground and background colors.
 
♦  Determine and set the current foreground and background mix modes.
 
Creating a Logical Color Table
 
To create a logical color table, you must perform the following tasks:
 
1  Create an array of RGB values that will replace the existing logical
   color table.
2  Call the GpiCreateLogColorTable function, using the LCOL_RESET and
   LCOLF_CONSECRGB flags.
 
The following code fragment demonstrates this process:
 
LONG alTable[] = {
    0xFFFFFF,  /* white */
    0xEDEDED,
    0xDBDBDB,
    0xC9C9C9,
    0xB7B7B7,
    0xA6A6A6,
    0x949494,
    0x828282,
    0x707070,
    0x5E5E5E,
    0x4D4D4D,
    0x3B3B3B,
    0x292929,
    0x171717,
    0x050505,
    0x000000 }; /* black */
 
GpiCreateLogColorTable(hps,
    LCOL_RESET,      /* begins with default         */
    LCOLF_CONSECRGB, /* consecutive RGB values      */
    0L,              /* starting index in table     */
    16L,             /* number of elements in table */
    alTable);
 
Determining the Color-Table Format and Index Values
 
To determine the format and the starting and ending index values of the
current logical color table, you can call the GpiQueryColorData function.
The following code fragment calls GpiQueryColorData to determine whether the
default logical color table is loaded and, if so, loads a new table:
 
LONG lClrData[3];
    .
    .
    .
GpiQueryColorData(hps, 3L, lClrData);
if (lClrData == LCOLF_DEFAULT)
    GpiCreateLogColorTable(hps,
        LCOL_RESET,      /* begins with default         */
        LCOLF_CONSECRGB, /* consecutive RGB values      */
        0L,              /* starting index in table     */
        16L,             /* number of elements in table */
        alTable);
 
Determining an Index Value for an RGB Value
 
To determine the logical-color-table index value associated with an RGB
value, you can call the GpiQueryColorIndex function. The following code
fragment shows how to determine which index value matches the RGB value for
pink (0x00FF00FF) and then use that index entry to set the foreground color
to pink for each of the primitive attributes:
 
LONG lIndex = 255;    /* logical-color-table index */
 
lIndex = GpiQueryColorIndex(hps, LCOLOPT_REALIZED, 0x00FF00FF);
if ((lIndex >= 0) && (lIndex <= 15))    /* checks for valid index */
    GpiSetColor(hps, lIndex);
 
Setting the Primitive Color Attributes
 
To set the color attributes for a single primitive, you can call the
GpiSetAttrs function, or you can set the color attributes for all of the
primitives in a presentation space by calling the GpiSetColor and
GpiSetBackColor functions.
 
The following code fragment shows how to use GpiSetAttrs to set the
line-primitive color attribute to dark gray:
 
LINEBUNDLE lbnd; /* line-primitive attribute bundle */
 
lbnd.lColor = CLR_DARKGRAY;
GpiSetAttrs(hps, PRIM_LINE, LBB_COLOR, 0L, &lbnd);
 
The next code fragment shows how to use GpiSetColor to set the foreground
color attribute for all of the primitives to dark gray:
 
GpiSetColor(hps, CLR_DARKGRAY);
 
 
                                      ♦