pixman: make shadow buffer optional

Add a flag to pixman-renderer for initializing the output with a shadow
framebuffer. All backends were getting the shadow implcitly, so all
backends are modified to ask for the shadow explicitly.

Using a shadow buffer is usually beneficial, because read-modify-write
cycles (blending) into a scanout-capable buffer may be very slow. The
scanout framebuffer may also have reduced color depth, making blending
and read-back produce inferior results.

In some use cases though the shadow buffer might be just an extra copy
hurting more than it helps. Whether it helps or hurts depends on the
platform and the workload. Therefore let the backends control whether
pixman-renderer uses a shadow buffer for an output or not.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Signed-off-by: Fabien Lahoudere <fabien.lahoudere@collabora.com>
Reviewed-by: Ian Ray <ian.ray@ge.com>

libweston/compositor-drm.c

@@ -4109,7 +4109,8 @@ drm_output_init_pixman(struct drm_output *output, struct drm_backend *b)
 			goto err;
 	}
 
-	if (pixman_renderer_output_create(&output->base) < 0)
+	if (pixman_renderer_output_create(&output->base,
+					  PIXMAN_RENDERER_OUTPUT_USE_SHADOW) < 0)
 		goto err;
 
 	pixman_region32_init_rect(&output->previous_damage,

libweston/compositor-fbdev.c

@@ -511,7 +511,8 @@ fbdev_output_enable(struct weston_output *base)
 	output->base.start_repaint_loop = fbdev_output_start_repaint_loop;
 	output->base.repaint = fbdev_output_repaint;
 
-	if (pixman_renderer_output_create(&output->base) < 0)
+	if (pixman_renderer_output_create(&output->base,
+					PIXMAN_RENDERER_OUTPUT_USE_SHADOW) < 0)
 		goto out_hw_surface;
 
 	loop = wl_display_get_event_loop(backend->compositor->wl_display);

libweston/compositor-headless.c

@@ -172,7 +172,8 @@ headless_output_enable(struct weston_output *base)
 							 output->image_buf,
 							 output->base.current_mode->width * 4);
 
-		if (pixman_renderer_output_create(&output->base) < 0)
+		if (pixman_renderer_output_create(&output->base,
+					PIXMAN_RENDERER_OUTPUT_USE_SHADOW) < 0)
 			goto err_renderer;
 
 		pixman_renderer_output_set_buffer(&output->base,

libweston/compositor-rdp.c

@@ -460,7 +460,7 @@ rdp_switch_mode(struct weston_output *output, struct weston_mode *target_mode)
 	output->current_mode->flags |= WL_OUTPUT_MODE_CURRENT;
 
 	pixman_renderer_output_destroy(output);
-	pixman_renderer_output_create(output);
+	pixman_renderer_output_create(output, PIXMAN_RENDERER_OUTPUT_USE_SHADOW);
 
 	new_shadow_buffer = pixman_image_create_bits(PIXMAN_x8r8g8b8, target_mode->width,
 			target_mode->height, 0, target_mode->width * 4);
@@ -546,7 +546,8 @@ rdp_output_enable(struct weston_output *base)
 		return -1;
 	}
 
-	if (pixman_renderer_output_create(&output->base) < 0) {
+	if (pixman_renderer_output_create(&output->base,
+					  PIXMAN_RENDERER_OUTPUT_USE_SHADOW) < 0) {
 		pixman_image_unref(output->shadow_surface);
 		return -1;
 	}

libweston/compositor-wayland.c

@@ -782,7 +782,8 @@ cleanup_window:
 static int
 wayland_output_init_pixman_renderer(struct wayland_output *output)
 {
-	return pixman_renderer_output_create(&output->base);
+	return pixman_renderer_output_create(&output->base,
+				     PIXMAN_RENDERER_OUTPUT_USE_SHADOW);
 }
 
 static void

libweston/compositor-x11.c

@@ -849,7 +849,8 @@ x11_output_switch_mode(struct weston_output *base, struct weston_mode *mode)
 			return -1;
 		}
 
-		if (pixman_renderer_output_create(&output->base) < 0) {
+		if (pixman_renderer_output_create(&output->base,
+				PIXMAN_RENDERER_OUTPUT_USE_SHADOW) < 0) {
 			weston_log("Failed to create pixman renderer for output\n");
 			x11_output_deinit_shm(b, output);
 			return -1;
@@ -1021,7 +1022,8 @@ x11_output_enable(struct weston_output *base)
 			weston_log("Failed to initialize SHM for the X11 output\n");
 			goto err;
 		}
-		if (pixman_renderer_output_create(&output->base) < 0) {
+		if (pixman_renderer_output_create(&output->base,
+				PIXMAN_RENDERER_OUTPUT_USE_SHADOW) < 0) {
 			weston_log("Failed to create pixman renderer for output\n");
 			x11_output_deinit_shm(b, output);
 			goto err;

libweston/pixman-renderer.c

@@ -337,13 +337,19 @@ repaint_region(struct weston_view *ev, struct weston_output *output,
 	struct pixman_surface_state *ps = get_surface_state(ev->surface);
 	struct pixman_output_state *po = get_output_state(output);
 	struct weston_buffer_viewport *vp = &ev->surface->buffer_viewport;
+	pixman_image_t *target_image;
 	pixman_transform_t transform;
 	pixman_filter_t filter;
 	pixman_image_t *mask_image;
 	pixman_color_t mask = { 0, };
 
+	if (po->shadow_image)
+		target_image = po->shadow_image;
+	else
+		target_image = po->hw_buffer;
+
  	/* Clip rendering to the damaged output region */
-	pixman_image_set_clip_region32(po->shadow_image, repaint_output);
+	pixman_image_set_clip_region32(target_image, repaint_output);
 
 	pixman_renderer_compute_transform(&transform, ev, output);
 
@@ -363,11 +369,11 @@ repaint_region(struct weston_view *ev, struct weston_output *output,
 	}
 
 	if (source_clip)
-		composite_clipped(ps->image, mask_image, po->shadow_image,
+		composite_clipped(ps->image, mask_image, target_image,
 				  &transform, filter, source_clip);
 	else
 		composite_whole(pixman_op, ps->image, mask_image,
-				po->shadow_image, &transform, filter);
+				target_image, &transform, filter);
 
 	if (mask_image)
 		pixman_image_unref(mask_image);
@@ -379,14 +385,14 @@ repaint_region(struct weston_view *ev, struct weston_output *output,
 		pixman_image_composite32(PIXMAN_OP_OVER,
 					 pr->debug_color, /* src */
 					 NULL /* mask */,
-					 po->shadow_image, /* dest */
+					 target_image, /* dest */
 					 0, 0, /* src_x, src_y */
 					 0, 0, /* mask_x, mask_y */
 					 0, 0, /* dest_x, dest_y */
-					 pixman_image_get_width (po->shadow_image), /* width */
-					 pixman_image_get_height (po->shadow_image) /* height */);
+					 pixman_image_get_width (target_image), /* width */
+					 pixman_image_get_height (target_image) /* height */);
 
-	pixman_image_set_clip_region32 (po->shadow_image, NULL);
+	pixman_image_set_clip_region32(target_image, NULL);
 }
 
 static void
@@ -575,9 +581,12 @@ pixman_renderer_repaint_output(struct weston_output *output,
 		pixman_region32_copy(&hw_damage, output_damage);
 	}
 
+	if (po->shadow_image) {
 		repaint_surfaces(output, output_damage);
-
 		copy_to_hw_buffer(output, &hw_damage);
+	} else {
+		repaint_surfaces(output, &hw_damage);
+	}
 	pixman_region32_fini(&hw_damage);
 
 	pixman_region32_copy(&output->previous_damage, output_damage);
@@ -902,7 +911,7 @@ pixman_renderer_output_set_hw_extra_damage(struct weston_output *output,
 }
 
 WL_EXPORT int
-pixman_renderer_output_create(struct weston_output *output)
+pixman_renderer_output_create(struct weston_output *output, uint32_t flags)
 {
 	struct pixman_output_state *po;
 	int w, h;
@@ -911,6 +920,7 @@ pixman_renderer_output_create(struct weston_output *output)
 	if (po == NULL)
 		return -1;
 
+	if (flags & PIXMAN_RENDERER_OUTPUT_USE_SHADOW) {
 		/* set shadow image transformation */
 		w = output->current_mode->width;
 		h = output->current_mode->height;
@@ -931,6 +941,7 @@ pixman_renderer_output_create(struct weston_output *output)
 			free(po);
 			return -1;
 		}
+	}
 
 	output->renderer_state = po;
 
@@ -942,6 +953,7 @@ pixman_renderer_output_destroy(struct weston_output *output)
 {
 	struct pixman_output_state *po = get_output_state(output);
 
+	if (po->shadow_image)
 		pixman_image_unref(po->shadow_image);
 
 	if (po->hw_buffer)

libweston/pixman-renderer.h

@@ -30,8 +30,12 @@
 int
 pixman_renderer_init(struct weston_compositor *ec);
 
+enum pixman_renderer_output_flags {
+	PIXMAN_RENDERER_OUTPUT_USE_SHADOW = (1 << 0),
+};
+
 int
-pixman_renderer_output_create(struct weston_output *output);
+pixman_renderer_output_create(struct weston_output *output, uint32_t flags);
 
 void
 pixman_renderer_output_set_buffer(struct weston_output *output,