XCB/ XCLCOLORMAP

The XCLCOLORMAP functions casts a Colormap object to an XCBCOLORMAP.

Function Prototype

static inline XCBCOLORMAP XCLCOLORMAP(Colormap src);

Example

#include <X11/xcl.h>
#include <stdlib.h>
#include <stdio.h>
#include <assert.h>

static const int red = 0xFFFF, green = 0x0, blue = 0x0; /* Test values. */

int main(void)
{
    Display *dpy = XOpenDisplay(NULL);
    int screen_num = DefaultScreen(dpy);
    XColor color;

    superduperColorAllocator(dpy, screen_num, &color);

    assert(color.red == red);
    assert(color.green == green);
    assert(color.blue == blue);

    printf("Closest supported color value = 0x%X\n"
           "Actual colors used:\n"
           "    red = 0x%X\n"
           "    green = 0x%X\n"
           "    blue = 0x%X\n", color.pixel, color.red, color.green, color.blue);

    return EXIT_SUCCESS;
}

Status superduperColorAllocator(Display* dpy, int screen_num, XColor *color)
{
    Status result;
    XCBConnection *c = XCBConnectionOfDisplay(dpy);
    XCBCOLORMAP cmap = XCLCOLORMAP(DefaultColormap(dpy, screen_num));
    XCBAllocColorCookie cookie = XCBAllocColor(c, cmap, red, green, blue);
    XCBAllocColorRep *color_rep = XCBAllocColorReply(c, cookie, 0);

    if (! color_rep)
        result = 0;
    else
    {
        result = 1;

        color->pixel = color_rep->pixel;
        color->red = color_rep->red;
        color->blue = color_rep->blue;
        color->green = color_rep->green;

        free(color_rep);
    }

    return result;
}

In this example, imagine the interface of superduperColorAllocator has been publicly released and can't be changed; however, since the XCL is binary compatible with Xlib, the internal implementation of this function can be ported to take advantage of XCB. Specifically, in this example, the result of DefaultColormap is cast from a Colormap to an XCBCOLORMAP using XCLCOLORMAP. After which, it allocates a new XCBAllocColorRep object using XCBAllocColor and XCBAllocColorReply in a way that is analogous to XAllocColor. This newly created XCBAllocColorRep object's data is then copied into the caller's XColor structure. Finally, like the Xlib's XAllocColor function, the new color must be freed because it is no longer needed. After returning to the client, the results are verified and printed.

See Also