dwm-flexipatch/patch/bar_alpha.c

static int useargb = 0;
static Visual *visual;
static int depth;
static Colormap cmap;

void
xinitvisual()
{
	XVisualInfo *infos;
	XRenderPictFormat *fmt;
	int nitems;
	int i;

	XVisualInfo tpl = {
		.screen = screen,
		.depth = 32,
		.class = TrueColor
	};
	long masks = VisualScreenMask | VisualDepthMask | VisualClassMask;

	infos = XGetVisualInfo(dpy, masks, &tpl, &nitems);
	visual = NULL;
	for (i = 0; i < nitems; i ++) {
		fmt = XRenderFindVisualFormat(dpy, infos[i].visual);
		if (fmt->type == PictTypeDirect && fmt->direct.alphaMask) {
			visual = infos[i].visual;
			depth = infos[i].depth;
			cmap = XCreateColormap(dpy, root, visual, AllocNone);
			useargb = 1;
			break;
		}
	}

	XFree(infos);

	if (!visual) {
		visual = DefaultVisual(dpy, screen);
		depth = DefaultDepth(dpy, screen);
		cmap = DefaultColormap(dpy, screen);
	}
}