Merge pull request #1167 from absolutelynothelix/xrender-cache-present-region

temporary workaround for #1166

src/backend/xrender/xrender.c

@@ -56,6 +56,10 @@ typedef struct _xrender_data {
 	int target_width, target_height;
 
 	xcb_special_event_t *present_event;
+
+	/// Cache an X region to avoid creating and destroying it every frame. A
+	/// workaround for yshui/picom#1166.
+	xcb_xfixes_region_t present_region;
 } xrender_data;
 
 struct _xrender_blur_context {
@@ -597,6 +601,7 @@ static void deinit(backend_t *backend_data) {
 			xcb_free_pixmap(xd->base.c->c, xd->back_pixmap[i]);
 		}
 	}
+	x_destroy_region(xd->base.c, xd->present_region);
 	if (xd->present_event) {
 		xcb_unregister_for_special_event(xd->base.c->c, xd->present_event);
 	}
@@ -624,16 +629,15 @@ static void present(backend_t *base, const region_t *region) {
 		                     XCB_NONE, xd->back[xd->curr_back], orig_x, orig_y, 0,
 		                     0, orig_x, orig_y, region_width, region_height);
 
-		auto xregion = x_create_region(base->c, region);
-
 		// Make sure we got reply from PresentPixmap before waiting for events,
 		// to avoid deadlock
 		auto e = xcb_request_check(
-		    base->c->c, xcb_present_pixmap_checked(
-		                    xd->base.c->c, xd->target_win,
-		                    xd->back_pixmap[xd->curr_back], 0, XCB_NONE, xregion, 0,
-		                    0, XCB_NONE, XCB_NONE, XCB_NONE, 0, 0, 0, 0, 0, NULL));
-		x_destroy_region(base->c, xregion);
+		    base->c->c,
+		    xcb_present_pixmap_checked(
+		        base->c->c, xd->target_win, xd->back_pixmap[xd->curr_back], 0, XCB_NONE,
+		        x_set_region(base->c, xd->present_region, region) ? xd->present_region
+		                                                          : XCB_NONE,
+		        0, 0, XCB_NONE, XCB_NONE, XCB_NONE, 0, 0, 0, 0, 0, NULL));
 		if (e) {
 			log_error("Failed to present pixmap");
 			free(e);
@@ -929,6 +933,10 @@ static backend_t *backend_xrender_init(session_t *ps, xcb_window_t target) {
 		xd->vsync = false;
 	}
 
+	if (xd->vsync) {
+		xd->present_region = x_create_region(&ps->c, &ps->screen_reg);
+	}
+
 	// We might need to do double buffering for vsync, and buffer 0 and 1 are for
 	// double buffering.
 	int first_buffer_index = xd->vsync ? 0 : 2;

src/x.c

@@ -459,6 +459,34 @@ bool x_fetch_region(struct x_connection *c, xcb_xfixes_region_t r, pixman_region
 	return ret;
 }
 
+bool x_set_region(struct x_connection *c, xcb_xfixes_region_t dst, const region_t *src) {
+	if (!src || dst == XCB_NONE) {
+		return false;
+	}
+
+	int32_t nrects = 0;
+	const rect_t *rects = pixman_region32_rectangles((region_t *)src, &nrects);
+	if (!rects || nrects < 1) {
+		return false;
+	}
+
+	xcb_rectangle_t *xrects = ccalloc(nrects, xcb_rectangle_t);
+	for (int32_t i = 0; i < nrects; i++) {
+		xrects[i] =
+		    (xcb_rectangle_t){.x = to_i16_checked(rects[i].x1),
+		                      .y = to_i16_checked(rects[i].y1),
+		                      .width = to_u16_checked(rects[i].x2 - rects[i].x1),
+		                      .height = to_u16_checked(rects[i].y2 - rects[i].y1)};
+	}
+
+	bool success =
+	    XCB_AWAIT_VOID(xcb_xfixes_set_region, c->c, dst, to_u32_checked(nrects), xrects);
+
+	free(xrects);
+
+	return success;
+}
+
 uint32_t x_create_region(struct x_connection *c, const region_t *reg) {
 	if (!reg) {
 		return XCB_NONE;

src/x.h

@@ -321,6 +321,9 @@ x_create_picture_with_visual(struct x_connection *, int w, int h, xcb_visualid_t
 /// Fetch a X region and store it in a pixman region
 bool x_fetch_region(struct x_connection *, xcb_xfixes_region_t r, region_t *res);
 
+/// Set an X region to a pixman region
+bool x_set_region(struct x_connection *c, xcb_xfixes_region_t dst, const region_t *src);
+
 /// Create a X region from a pixman region
 uint32_t x_create_region(struct x_connection *c, const region_t *reg);