Creating a Palette

To create a palette, an application must first call DevQueryCaps with the CAPS_ADDITIONAL_GRAPHICS option to determine whether the device supports palette functions. Next the application creates an array of RGB values or an array of RGB2 structures, then calls GpiCreatePalette. Next the applications calls GpiSelectPalette to select the palette for the presentation space and calls WinRealizePalette to map the RGB values to device colors for subsequent drawing. When the application is finished drawing, it calls GpiSelectPalette to disassociate the presentation space and the palette. Then it deletes the palette by calling GpiDeletePalette.

The following figure demonstrates these steps.

#define INCL_GPILOGCOLORTABLE
#define INCL_GPIBITMAPS
#include <os2.h>
void fncCOLR06(void){
    COLOR clrCurrent;
    HPAL hpal;
    HDC hdc;
    HPS hps;
    HAB hab;
    HWND hwnd;
    POINTL aptl[2], ptl;
    LONG cSimulColors, lPalSupport;
    SHORT j;
    RGB2 *prgb2ColorData;

    /* Determine how many colors the device can display at once.              */
    DevQueryCaps(hdc, CAPS_COLORS, 1, &cSimulColors);

    /* Determine if the device supports palette manager functions.            */
    DevQueryCaps(hdc, CAPS_ADDITIONAL_GRAPHICS, 1, &lPalSupport);

    /* Allocate space for the array of RGB2 structures.                       */
    DosAllocMem((PPVOID)&prgb2ColorData, cSimulColors * sizeof(RGB2), fALLOC);

    /* Fill the array of RGB2 structures with as many different               */
    /*    shades of blue as the device will support.                          */

    clrCurrent = 0x000000FF;
    for (j = 0; j < cSimulColors; j++) {
        prgb2ColorData[j].bRed = 0;
        prgb2ColorData[j].bGreen = 0;
        prgb2ColorData[j].bBlue = clrCurrent;
        prgb2ColorData[j].fcOptions = 0;
        clrCurrent = clrCurrent > 0 ? --clrCurrent : 0x000000FF;
    }

    if (lPalSupport & CAPS_PALETTE_MANAGER) {
        hpal = GpiCreatePalette(hab,       /* Create palette                  */
               0L,
               LCOLF_CONSECRGB,            /* Format of color table entries   */
               cSimulColors,               /* Number of entries in table      */
               (PULONG) prgb2ColorData);   /* Pointer to color table          */
    }

    GpiSelectPalette(hps, hpal);
    WinRealizePalette(hwnd, hps);
    GpiSelectPalette(hps, NULLHANDLE);     /* Restore default physical colors */
    GpiDeletePalette(hpal);                /* Delete palette                  */
} /* fncCOLR06 */