Hi, I am trying to find out whether I can use Render to modify the alpha
channel in a frame buffer that's in ARGB 8888 format. I modified Keith's
sample code slightly to render a red rectangle into the frame buffer with
the destination alpha set to 0x80. But I get 0x00FF0000 in the frame buffer
instead of the desired 0x80FF0000.
I have included the test program below. Is there any way to do this with
Render/fb or does it require special hacks?
Jonathan Bian
#include <X11/Xlib.h>
#include <X11/extensions/Xrender.h>
Pixmap color_pix;
Picture color;
Window window;
Picture picture;
Display *dpy;
int screen;
Visual *visual;
XRenderPictFormat *format_win, *format_pix;
#define SIZE 200
main ()
{
XRenderPictureAttributes pa;
XRenderPictFormat pf;
XEvent ev;
XRenderColor rc;
rc.red = 0xffff;
rc.green = 0x0;
rc.blue = 0x0;
rc.alpha = 0x8000;
dpy = XOpenDisplay (0);
XSynchronize (dpy, 1);
if (!dpy) exit(1);
screen = DefaultScreen (dpy);
visual = DefaultVisual (dpy, screen);
format_win = XRenderFindVisualFormat (dpy, visual);
if (!format_win) exit(1);
pf.depth = 32;
pf.type = PictTypeDirect;
pf.direct.alpha = 24;
pf.direct.alphaMask = 0xff;
pf.direct.red = 16;
pf.direct.redMask = 0xff;
pf.direct.green = 8;
pf.direct.greenMask = 0xff;
pf.direct.blue = 0;
pf.direct.blueMask = 0xff;
format_pix = XRenderFindFormat(dpy,
PictFormatType|
PictFormatDepth|
PictFormatRed|
PictFormatRedMask|
PictFormatGreen|
PictFormatGreenMask|
PictFormatBlue|
PictFormatBlueMask|
PictFormatAlpha|
PictFormatAlphaMask,
&pf, 0);
if (!format_pix) exit (1);
window = XCreateSimpleWindow(dpy, RootWindow (dpy, screen),
0, 0, SIZE, SIZE, 1, BlackPixel (dpy,
screen),
WhitePixel (dpy, screen));
picture = XRenderCreatePicture (dpy, window, format_win, 0, 0);
color_pix = XCreatePixmap(dpy, window, 1, 1, 32);
pa.repeat = True;
color = XRenderCreatePicture (dpy, color_pix, format_pix,
CPRepeat, &pa);
XSelectInput (dpy, window, ExposureMask);
XMapWindow (dpy, window);
for (;;)
{
XNextEvent (dpy, &ev);
if (ev.type == Expose && ev.xexpose.count == 0)
{
XClearArea (dpy, window, 0, 0, 0, 0, False);
XRenderFillRectangle(dpy, PictOpSrc, color, &rc, 0, 0, 1, 1);
XRenderComposite (dpy,
PictOpSrc,
color,
0,
picture,
0, 0, 0, 0, 0, 0, SIZE, SIZE);
}
}
}
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