wmaker: set the color pixel for TrueColor display

As mentioned in commit 67e2f5e1ca,
for TrueColor display it's not necessary to allocate a color but
it is required to set the pixel property of the XColor.

src/resources.c

@@ -35,20 +35,41 @@
 #include "resources.h"
 #include "screen.h"
 
+static unsigned long scale_color_component(unsigned short value, unsigned long mask)
+{
+	unsigned long m = mask;
+	int shift = 0, bits = 0;
+
+	if (!m)
+		return 0;
+
+	while (!(m & 1)) {
+		shift++;
+		m >>= 1;
+	}
+	while (m) {
+		bits++;
+		m >>= 1;
+	}
+
+	return ((unsigned long)(value >> (16 - bits)) & ((1UL << bits) - 1)) << shift;
+}
+
 int wGetColorForColormap(WScreen *scr, Colormap colormap, const char *color_name, XColor *color)
 {
-	if (scr->w_visual->class == TrueColor) {
-		XColor dummy_exact;
-		if (!XLookupColor(dpy, colormap, color_name, &dummy_exact, color)) {
-			wwarning(_("could not lookup color \"%s\""), color_name);
-			return False;
-		}
-		return True;
-	}
 	if (!XParseColor(dpy, colormap, color_name, color)) {
 		wwarning(_("could not parse color \"%s\""), color_name);
 		return False;
 	}
+
+	if (scr->w_visual->class == TrueColor) {
+		/* Compute pixel directly from RGB components using the visual's channel masks */
+		color->pixel = scale_color_component(color->red,   scr->w_visual->red_mask)
+		             | scale_color_component(color->green, scr->w_visual->green_mask)
+		             | scale_color_component(color->blue,  scr->w_visual->blue_mask);
+		return True;
+	}
+
 	if (!XAllocColor(dpy, colormap, color)) {
 		wwarning(_("could not allocate color \"%s\""), color_name);
 		return False;