render: fix root back pixmap binding in case of depth mismatch

backport of the previous commit to legacy backends. it also eliminates
the x_validate_pixmap function since it was only used in the
get_root_tile function and the fix implies and embeds it.

src/render.c

@@ -597,26 +597,32 @@ static bool get_root_tile(session_t *ps) {
 	bool fill = false;
 	xcb_pixmap_t pixmap = x_get_root_back_pixmap(ps->c, ps->root, 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, xcb_get_geometry(ps->c, pixmap), NULL);
+	}
 
 	// Create a pixmap if there isn't any
-	if (!pixmap) {
+	xcb_visualid_t vis;
+	if (!pixmap || !r) {
 		pixmap = x_create_pixmap(ps->c, (uint8_t)ps->depth, ps->root, 1, 1);
 		if (pixmap == XCB_NONE) {
 			log_error("Failed to create pixmaps for root tile.");
 			return false;
 		}
+		vis = ps->vis;
 		fill = true;
+	} else {
+		vis = x_get_visual_for_depth(ps->c, r->depth);
+		free(r);
 	}
 
 	// Create Picture
 	xcb_render_create_picture_value_list_t pa = {
 	    .repeat = true,
 	};
 	ps->root_tile_paint.pict = x_create_picture_with_visual_and_pixmap(
-	    ps->c, ps->vis, pixmap, XCB_RENDER_CP_REPEAT, &pa);
+	    ps->c, vis, pixmap, XCB_RENDER_CP_REPEAT, &pa);
 
 	// Fill pixmap if needed
 	if (fill) {
@@ -637,7 +643,7 @@ 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->vis, false);
+		return paint_bind_tex(ps, &ps->root_tile_paint, 0, 0, true, 0, vis, false);
 #endif
 
 	return true;

src/x.c

@@ -622,26 +622,6 @@ xcb_pixmap_t x_create_pixmap(xcb_connection_t *c, uint8_t depth, xcb_drawable_t
 	return XCB_NONE;
 }
 
-/**
- * Validate a pixmap.
- *
- * Detect whether the pixmap is valid with XGetGeometry. Well, maybe there
- * are better ways.
- */
-bool x_validate_pixmap(xcb_connection_t *c, xcb_pixmap_t pixmap) {
-	if (pixmap == XCB_NONE) {
-		return false;
-	}
-
-	auto r = xcb_get_geometry_reply(c, xcb_get_geometry(c, pixmap), NULL);
-	if (!r) {
-		return false;
-	}
-
-	bool ret = r->width && r->height;
-	free(r);
-	return ret;
-}
 /// Names of root window properties that could point to a pixmap of
 /// background.
 static const char *background_props_str[] = {

src/x.h

@@ -245,8 +245,6 @@ const char *x_strerror(xcb_generic_error_t *e);
 xcb_pixmap_t x_create_pixmap(xcb_connection_t *, uint8_t depth, xcb_drawable_t drawable,
                              int width, int height);
 
-bool x_validate_pixmap(xcb_connection_t *, xcb_pixmap_t pxmap);
-
 /**
  * Free a <code>winprop_t</code>.
  *