pixman-renderer: implement source clipping

Implement a way to do composition clipping with a region32 given in
source image space.

Pixman does not directly support this kind of operation at all. If you
pixman_image_set_clip_region32() on a source image, it will be ignored
unless you also
	pixman_image_set_source_clipping(image, 1);
	pixman_image_set_has_client_clip(image, 1);
but then it takes the region from source image and still uses it in the
destination coordinate space. For reference:
http://lists.freedesktop.org/archives/pixman/2015-March/003501.html
That is actually the intended behaviour in Pixman.

This patch implements source clipping by taking each rectangle of the
source clip region, wrapping that sub-rect of the source image in a new
pixman_image_t, and compositing it separately. This might be very heavy as
we are painting the whole damage the number of rectangles times, but
practically always the number of rectangles is one.

An alternative solution would be to use mask images of type PIXMAN_a1,
render the source clip region in it, and set the transformation. You'd
probably also want to cache those images. And because we use the mask to
apply view->alpha, you'd have to use PIXMAN_a8 in those cases.

v2: Fix a comment.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-By: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/pixman-renderer.c

@@ -211,16 +211,114 @@ region_intersect_only_translation(pixman_region32_t *result_global,
 	pixman_region32_intersect(result_global, result_global, global);
 }
 
+static void
+composite_whole(pixman_op_t op,
+		pixman_image_t *src,
+		pixman_image_t *mask,
+		pixman_image_t *dest,
+		const pixman_transform_t *transform,
+		pixman_filter_t filter)
+{
+	int32_t dest_width;
+	int32_t dest_height;
+
+	dest_width = pixman_image_get_width(dest);
+	dest_height = pixman_image_get_height(dest);
+
+	pixman_image_set_transform(src, transform);
+	pixman_image_set_filter(src, filter, NULL, 0);
+
+	pixman_image_composite32(op, src, mask, dest,
+				 0, 0, /* src_x, src_y */
+				 0, 0, /* mask_x, mask_y */
+				 0, 0, /* dest_x, dest_y */
+				 dest_width, dest_height);
+}
+
+static void
+composite_clipped(pixman_image_t *src,
+		  pixman_image_t *mask,
+		  pixman_image_t *dest,
+		  const pixman_transform_t *transform,
+		  pixman_filter_t filter,
+		  pixman_region32_t *src_clip)
+{
+	int n_box;
+	pixman_box32_t *boxes;
+	int32_t dest_width;
+	int32_t dest_height;
+	int src_stride;
+	int bitspp;
+	pixman_format_code_t src_format;
+	void *src_data;
+	int i;
+
+	/* Hardcoded to use PIXMAN_OP_OVER, because sampling outside of
+	 * a Pixman image produces (0,0,0,0) instead of discarding the
+	 * fragment.
+	 */
+
+	dest_width = pixman_image_get_width(dest);
+	dest_height = pixman_image_get_height(dest);
+	src_format = pixman_image_get_format(src);
+	src_stride = pixman_image_get_stride(src);
+	bitspp = PIXMAN_FORMAT_BPP(src_format);
+	src_data = pixman_image_get_data(src);
+
+	assert(src_format);
+
+	/* This would be massive overdraw, except when n_box is 1. */
+	boxes = pixman_region32_rectangles(src_clip, &n_box);
+	for (i = 0; i < n_box; i++) {
+		uint8_t *ptr = src_data;
+		pixman_image_t *boximg;
+		pixman_transform_t adj = *transform;
+
+		ptr += boxes[i].y1 * src_stride;
+		ptr += boxes[i].x1 * bitspp / 8;
+		boximg = pixman_image_create_bits_no_clear(src_format,
+					boxes[i].x2 - boxes[i].x1,
+					boxes[i].y2 - boxes[i].y1,
+					(uint32_t *)ptr, src_stride);
+
+		pixman_transform_translate(&adj, NULL,
+					   pixman_int_to_fixed(-boxes[i].x1),
+					   pixman_int_to_fixed(-boxes[i].y1));
+		pixman_image_set_transform(boximg, &adj);
+
+		pixman_image_set_filter(boximg, filter, NULL, 0);
+		pixman_image_composite32(PIXMAN_OP_OVER, boximg, mask, dest,
+					 0, 0, /* src_x, src_y */
+					 0, 0, /* mask_x, mask_y */
+					 0, 0, /* dest_x, dest_y */
+					 dest_width, dest_height);
+
+		pixman_image_unref(boximg);
+	}
+
+	if (n_box > 1) {
+		static bool warned = false;
+
+		if (!warned)
+			weston_log("Pixman-renderer warning: %dx overdraw\n",
+				   n_box);
+		warned = true;
+	}
+}
+
 /** Paint an intersected region
  *
  * \param ev The view to be painted.
  * \param output The output being painted.
  * \param repaint_output The region to be painted in output coordinates.
+ * \param source_clip The region of the source image to use, in source image
+ *                    coordinates. If NULL, use the whole source image.
  * \param pixman_op Compositing operator, either SRC or OVER.
  */
 static void
 repaint_region(struct weston_view *ev, struct weston_output *output,
 	       pixman_region32_t *repaint_output,
+	       pixman_region32_t *source_clip,
 	       pixman_op_t pixman_op)
 {
 	struct pixman_renderer *pr =
@@ -229,6 +327,7 @@ repaint_region(struct weston_view *ev, struct weston_output *output,
 	struct pixman_output_state *po = get_output_state(output);
 	struct weston_buffer_viewport *vp = &ev->surface->buffer_viewport;
 	pixman_transform_t transform;
+	pixman_filter_t filter;
 	pixman_image_t *mask_image;
 	pixman_color_t mask = { 0, };
 
@@ -236,12 +335,11 @@ repaint_region(struct weston_view *ev, struct weston_output *output,
 	pixman_image_set_clip_region32(po->shadow_image, repaint_output);
 
 	pixman_renderer_compute_transform(&transform, ev, output);
-	pixman_image_set_transform(ps->image, &transform);
 
 	if (ev->transform.enabled || output->current_scale != vp->buffer.scale)
-		pixman_image_set_filter(ps->image, PIXMAN_FILTER_BILINEAR, NULL, 0);
+		filter = PIXMAN_FILTER_BILINEAR;
 	else
-		pixman_image_set_filter(ps->image, PIXMAN_FILTER_NEAREST, NULL, 0);
+		filter = PIXMAN_FILTER_NEAREST;
 
 	if (ps->buffer_ref.buffer)
 		wl_shm_buffer_begin_access(ps->buffer_ref.buffer->shm_buffer);
@@ -253,15 +351,12 @@ repaint_region(struct weston_view *ev, struct weston_output *output,
 		mask_image = NULL;
 	}
 
-	pixman_image_composite32(pixman_op,
+	if (source_clip)
-				 ps->image, /* src */
+		composite_clipped(ps->image, mask_image, po->shadow_image,
-				 mask_image, /* mask */
+				  &transform, filter, source_clip);
-				 po->shadow_image, /* dest */
+	else
-				 0, 0, /* src_x, src_y */
+		composite_whole(pixman_op, ps->image, mask_image,
-				 0, 0, /* mask_x, mask_y */
+				po->shadow_image, &transform, filter);
-				 0, 0, /* dest_x, dest_y */
-				 pixman_image_get_width (po->shadow_image), /* width */
-				 pixman_image_get_height (po->shadow_image) /* height */);
 
 	if (mask_image)
 		pixman_image_unref(mask_image);
@@ -312,7 +407,7 @@ draw_view_translated(struct weston_view *view, struct weston_output *output,
 							  view);
 			region_global_to_output(output, &repaint_output);
 
-			repaint_region(view, output, &repaint_output,
+			repaint_region(view, output, &repaint_output, NULL,
 				       PIXMAN_OP_SRC);
 		}
 	}
@@ -323,7 +418,7 @@ draw_view_translated(struct weston_view *view, struct weston_output *output,
 						  &surface_blend, view);
 		region_global_to_output(output, &repaint_output);
 
-		repaint_region(view, output, &repaint_output,
+		repaint_region(view, output, &repaint_output, NULL,
 			       PIXMAN_OP_OVER);
 	}
 
@@ -331,6 +426,38 @@ draw_view_translated(struct weston_view *view, struct weston_output *output,
 	pixman_region32_fini(&repaint_output);
 }
 
+static void
+draw_view_source_clipped(struct weston_view *view,
+			 struct weston_output *output,
+			 pixman_region32_t *repaint_global)
+{
+	struct weston_surface *surface = view->surface;
+	pixman_region32_t surf_region;
+	pixman_region32_t buffer_region;
+	pixman_region32_t repaint_output;
+
+	/* Do not bother separating the opaque region from non-opaque.
+	 * Source clipping requires PIXMAN_OP_OVER in all cases, so painting
+	 * opaque separately has no benefit.
+	 */
+
+	pixman_region32_init_rect(&surf_region, 0, 0,
+				  surface->width, surface->height);
+	pixman_region32_init(&buffer_region);
+	weston_surface_to_buffer_region(surface, &surf_region, &buffer_region);
+
+	pixman_region32_init(&repaint_output);
+	pixman_region32_copy(&repaint_output, repaint_global);
+	region_global_to_output(output, &repaint_output);
+
+	repaint_region(view, output, &repaint_output, &buffer_region,
+		       PIXMAN_OP_OVER);
+
+	pixman_region32_fini(&repaint_output);
+	pixman_region32_fini(&buffer_region);
+	pixman_region32_fini(&surf_region);
+}
+
 static void
 draw_view(struct weston_view *ev, struct weston_output *output,
 	  pixman_region32_t *damage) /* in global coordinates */
@@ -357,12 +484,22 @@ draw_view(struct weston_view *ev, struct weston_output *output,
 		zoom_logged = 1;
 	}
 
-	/* TODO: Implement repaint_region_complex() using pixman_composite_trapezoids() */
 	if (view_transformation_is_translation(ev)) {
+		/* The simple case: The surface regions opaque, non-opaque,
+		 * etc. are convertible to global coordinate space.
+		 * There is no need to use a source clip region.
+		 * It is possible to paint opaque region as PIXMAN_OP_SRC.
+		 */
 		draw_view_translated(ev, output, &repaint);
 	} else {
-		region_global_to_output(output, &repaint);
+		/* The complex case: the view transformation does not allow
-		repaint_region(ev, output, &repaint, PIXMAN_OP_OVER);
+		 * converting opaque etc. regions into global coordinate space.
+		 * Therefore we need source clipping to avoid sampling from
+		 * unwanted source image areas, unless the source image is
+		 * to be used whole. Source clipping does not work with
+		 * PIXMAN_OP_SRC.
+		 */
+		draw_view_source_clipped(ev, output, &repaint);
 	}
 
 out: