render: fix binding the root background pixmap in case of depth mismatch

fix the same issue in the legacy backends, see the previous commit for
details. this commit also removes the x_validate_pixmap function because
it was used only in the get_root_tile function and the fix pretty much
implies and embeds it.

src/render.c

@@ -604,20 +604,27 @@ static bool get_root_tile(session_t *ps) {
 	bool fill = false;
 	xcb_pixmap_t pixmap = x_get_root_back_pixmap(&ps->c, ps->atoms);
 
-	// Make sure the pixmap we got is valid
-	if (pixmap && !x_validate_pixmap(&ps->c, pixmap)) {
-		pixmap = XCB_NONE;
+	xcb_get_geometry_reply_t *r;
+	if (pixmap) {
+		r = xcb_get_geometry_reply(ps->c.c, xcb_get_geometry(ps->c.c, pixmap), NULL);
 	}
 
 	// Create a pixmap if there isn't any
-	if (!pixmap) {
+	xcb_visualid_t visual;
+	if (!pixmap || !r) {
 		pixmap =
 		    x_create_pixmap(&ps->c, (uint8_t)ps->c.screen_info->root_depth, 1, 1);
 		if (pixmap == XCB_NONE) {
 			log_error("Failed to create pixmaps for root tile.");
 			return false;
 		}
+		visual = ps->c.screen_info->root_visual;
 		fill = true;
+	} else {
+		visual = r->depth == ps->c.screen_info->root_depth
+		             ? ps->c.screen_info->root_visual
+		             : x_get_visual_for_depth(&ps->c, r->depth);
+		free(r);
 	}
 
 	// Create Picture
@@ -625,7 +632,7 @@ static bool get_root_tile(session_t *ps) {
 	    .repeat = true,
 	};
 	ps->root_tile_paint.pict = x_create_picture_with_visual_and_pixmap(
-	    &ps->c, ps->c.screen_info->root_visual, pixmap, XCB_RENDER_CP_REPEAT, &pa);
+	    &ps->c, visual, pixmap, XCB_RENDER_CP_REPEAT, &pa);
 
 	// Fill pixmap if needed
 	if (fill) {
@@ -646,8 +653,7 @@ static bool get_root_tile(session_t *ps) {
 	ps->root_tile_paint.pixmap = pixmap;
 #ifdef CONFIG_OPENGL
 	if (BKEND_GLX == ps->o.backend) {
-		return paint_bind_tex(ps, &ps->root_tile_paint, 0, 0, true, 0,
-		                      ps->c.screen_info->root_visual, false);
+		return paint_bind_tex(ps, &ps->root_tile_paint, 0, 0, true, 0, visual, false);
 	}
 #endif
 

src/x.c

@@ -704,27 +704,6 @@ xcb_pixmap_t x_create_pixmap(struct x_connection *c, uint8_t depth, int width, i
 	return XCB_NONE;
 }
 
-/**
- * Validate a pixmap.
- *
- * Detect whether the pixmap is valid with XGetGeometry. Well, maybe there
- * are better ways.
- */
-bool x_validate_pixmap(struct x_connection *c, xcb_pixmap_t pixmap) {
-	if (pixmap == XCB_NONE) {
-		return false;
-	}
-
-	auto r = xcb_get_geometry_reply(c->c, xcb_get_geometry(c->c, pixmap), NULL);
-	if (!r) {
-		return false;
-	}
-
-	bool ret = r->width && r->height;
-	free(r);
-	return ret;
-}
-
 /// We don't use the _XSETROOT_ID root window property as a source of the background
 /// pixmap because it most likely points to a dummy pixmap used to keep the colormap
 /// associated with the background pixmap alive but we listen for it's changes and update

src/x.h

@@ -356,8 +356,6 @@ const char *x_strerror(xcb_generic_error_t *e);
 
 xcb_pixmap_t x_create_pixmap(struct x_connection *, uint8_t depth, int width, int height);
 
-bool x_validate_pixmap(struct x_connection *, xcb_pixmap_t pxmap);
-
 /**
  * Free a <code>winprop_t</code>.
  *