libweston: introduce weston_paint_node

This new object is created for every surface-view-output triplet. As
there is always exactly one surface for a view and it does not change
during a view's lifetime, this is really for a view-output pair or a
surface-output pair.

The object is created on-demand as a part of preparing for an output
repaint, so it applies only to surfaces that are going through repaint.
A prerequisite for that is that the surface is mapped, which means it
has a mapped view.

When any one of surface or view gets destroyed or output gets disabled,
all related paint nodes are destroyed.

In future, paint node will be useful for caching surface-output or
view-output pair dependent data:
- damage regions for overlapping outputs
- color transformations
- backend-specific bookkeeping (e.g. DRM KMS plane assigments)
- per-output repaint lists
- surface geometry transformed into output space

Suggested by Daniel Stone in
https://gitlab.freedesktop.org/wayland/weston/-/merge_requests/582#note_899406

PS. The call in weston_view_destroy() to
weston_compositor_build_view_list() might be so that if the view has
sub-surfaces, rebuilding the view list removes those those too and
automagically deletes their views.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

include/libweston/libweston.h

@@ -1,6 +1,6 @@
 /*
  * Copyright © 2008-2011 Kristian Høgsberg
- * Copyright © 2012, 2017, 2018 Collabora, Ltd.
+ * Copyright © 2012, 2017, 2018, 2021 Collabora, Ltd.
  * Copyright © 2017, 2018 General Electric Company
  *
  * Permission is hereby granted, free of charge, to any person obtaining
@@ -280,6 +280,9 @@ struct weston_output {
 	struct wl_list link;
 	struct weston_compositor *compositor;
 
+	/* struct weston_paint_node::output_link */
+	struct wl_list paint_node_list;
+
 	/** From global to output buffer coordinates. */
 	struct weston_matrix matrix;
 	/** From output buffer to global coordinates. */
@@ -1268,6 +1271,9 @@ struct weston_view {
 	struct wl_list surface_link;
 	struct wl_signal destroy_signal;
 
+	/* struct weston_paint_node::view_link */
+	struct wl_list paint_node_list;
+
 	struct wl_list link;             /* weston_compositor::view_list */
 	struct weston_layer_entry layer_link; /* part of geometry */
 	struct weston_plane *plane;
@@ -1427,6 +1433,9 @@ struct weston_surface {
 	struct weston_compositor *compositor;
 	struct wl_signal commit_signal;
 
+	/* struct weston_paint_node::surface_link */
+	struct wl_list paint_node_list;
+
 	/** Damage in local coordinates from the client, for tex upload. */
 	pixman_region32_t damage;
 

libweston/compositor.c

@@ -1,7 +1,7 @@
 /*
  * Copyright © 2010-2011 Intel Corporation
  * Copyright © 2008-2011 Kristian Høgsberg
- * Copyright © 2012-2018 Collabora, Ltd.
+ * Copyright © 2012-2018, 2021 Collabora, Ltd.
  * Copyright © 2017, 2018 General Electric Company
  *
  * Permission is hereby granted, free of charge, to any person obtaining
@@ -93,11 +93,47 @@ weston_output_transform_scale_init(struct weston_output *output,
 				   uint32_t transform, uint32_t scale);
 
 static void
-weston_compositor_build_view_list(struct weston_compositor *compositor);
+weston_compositor_build_view_list(struct weston_compositor *compositor,
+				  struct weston_output *output);
 
 static char *
 weston_output_create_heads_string(struct weston_output *output);
 
+static struct weston_paint_node *
+weston_paint_node_create(struct weston_surface *surface,
+			 struct weston_view *view,
+			 struct weston_output *output)
+{
+	struct weston_paint_node *pnode;
+
+	assert(view->surface == surface);
+
+	pnode = zalloc(sizeof *pnode);
+	if (!pnode)
+		return NULL;
+
+	pnode->surface = surface;
+	wl_list_insert(&surface->paint_node_list, &pnode->surface_link);
+
+	pnode->view = view;
+	wl_list_insert(&view->paint_node_list, &pnode->view_link);
+
+	pnode->output = output;
+	wl_list_insert(&output->paint_node_list, &pnode->output_link);
+
+	return pnode;
+}
+
+static void
+weston_paint_node_destroy(struct weston_paint_node *pnode)
+{
+	assert(pnode->view->surface == pnode->surface);
+	wl_list_remove(&pnode->surface_link);
+	wl_list_remove(&pnode->view_link);
+	wl_list_remove(&pnode->output_link);
+	free(pnode);
+}
+
 /** Send wl_output events for mode and scale changes
  *
  * \param head Send on all resources bound to this head.
@@ -336,6 +372,7 @@ weston_view_create(struct weston_surface *surface)
 	wl_signal_init(&view->destroy_signal);
 	wl_list_init(&view->link);
 	wl_list_init(&view->layer_link.link);
+	wl_list_init(&view->paint_node_list);
 
 	pixman_region32_init(&view->clip);
 
@@ -553,6 +590,7 @@ weston_surface_create(struct weston_compositor *compositor)
 	region_init_infinite(&surface->input);
 
 	wl_list_init(&surface->views);
+	wl_list_init(&surface->paint_node_list);
 
 	wl_list_init(&surface->frame_callback_list);
 	wl_list_init(&surface->feedback_list);
@@ -1951,6 +1989,23 @@ weston_view_matches_output_entirely(struct weston_view *ev,
 	return true;
 }
 
+/** Find paint node for the given view and output
+ */
+WL_EXPORT struct weston_paint_node *
+weston_view_find_paint_node(struct weston_view *view,
+			    struct weston_output *output)
+{
+	struct weston_paint_node *pnode;
+
+	wl_list_for_each(pnode, &view->paint_node_list, view_link) {
+		assert(pnode->surface == view->surface);
+		if (pnode->output == output)
+			return pnode;
+	}
+
+	return NULL;
+}
+
 /* Check if a surface has a view assigned to it
  *
  * The indicator is set manually when mapping
@@ -2192,15 +2247,21 @@ weston_surface_reset_pending_buffer(struct weston_surface *surface)
 WL_EXPORT void
 weston_view_destroy(struct weston_view *view)
 {
+	struct weston_paint_node *pnode, *pntmp;
+
 	wl_signal_emit(&view->destroy_signal, view);
 
 	assert(wl_list_empty(&view->geometry.child_list));
 
 	if (weston_view_is_mapped(view)) {
 		weston_view_unmap(view);
-		weston_compositor_build_view_list(view->surface->compositor);
+		weston_compositor_build_view_list(view->surface->compositor,
+						  NULL);
 	}
 
+	wl_list_for_each_safe(pnode, pntmp, &view->paint_node_list, view_link)
+		weston_paint_node_destroy(pnode);
+
 	wl_list_remove(&view->link);
 	weston_layer_entry_remove(&view->layer_link);
 
@@ -2223,6 +2284,7 @@ weston_surface_destroy(struct weston_surface *surface)
 	struct weston_frame_callback *cb, *next;
 	struct weston_view *ev, *nv;
 	struct weston_pointer_constraint *constraint, *next_constraint;
+	struct weston_paint_node *pnode, *pntmp;
 
 	if (--surface->ref_count > 0)
 		return;
@@ -2237,6 +2299,11 @@ weston_surface_destroy(struct weston_surface *surface)
 	wl_list_for_each_safe(ev, nv, &surface->views, surface_link)
 		weston_view_destroy(ev);
 
+	wl_list_for_each_safe(pnode, pntmp,
+			      &surface->paint_node_list, surface_link) {
+		weston_paint_node_destroy(pnode);
+	}
+
 	weston_surface_state_fini(&surface->pending);
 
 	weston_buffer_reference(&surface->buffer_ref, NULL);
@@ -2594,10 +2661,26 @@ surface_free_unused_subsurface_views(struct weston_surface *surface)
 	}
 }
 
+static struct weston_paint_node *
+view_ensure_paint_node(struct weston_view *view, struct weston_output *output)
+{
+	struct weston_paint_node *pnode;
+
+	if (!output)
+		return NULL;
+
+	pnode = weston_view_find_paint_node(view, output);
+	if (pnode)
+		return pnode;
+
+	return weston_paint_node_create(view->surface, view, output);
+}
+
 static void
 view_list_add_subsurface_view(struct weston_compositor *compositor,
 			      struct weston_subsurface *sub,
-			      struct weston_view *parent)
+			      struct weston_view *parent,
+			      struct weston_output *output)
 {
 	struct weston_subsurface *child;
 	struct weston_view *view = NULL, *iv;
@@ -2627,6 +2710,7 @@ view_list_add_subsurface_view(struct weston_compositor *compositor,
 	view->parent_view = parent;
 	weston_view_update_transform(view);
 	view->is_mapped = true;
+	view_ensure_paint_node(view, output);
 
 	if (wl_list_empty(&sub->surface->subsurface_list)) {
 		wl_list_insert(compositor->view_list.prev, &view->link);
@@ -2637,7 +2721,7 @@ view_list_add_subsurface_view(struct weston_compositor *compositor,
 		if (child->surface == sub->surface)
 			wl_list_insert(compositor->view_list.prev, &view->link);
 		else
-			view_list_add_subsurface_view(compositor, child, view);
+			view_list_add_subsurface_view(compositor, child, view, output);
 	}
 }
 
@@ -2649,11 +2733,13 @@ view_list_add_subsurface_view(struct weston_compositor *compositor,
  */
 static void
 view_list_add(struct weston_compositor *compositor,
-	      struct weston_view *view)
+	      struct weston_view *view,
+	      struct weston_output *output)
 {
 	struct weston_subsurface *sub;
 
 	weston_view_update_transform(view);
+	view_ensure_paint_node(view, output);
 
 	if (wl_list_empty(&view->surface->subsurface_list)) {
 		wl_list_insert(compositor->view_list.prev, &view->link);
@@ -2664,12 +2750,13 @@ view_list_add(struct weston_compositor *compositor,
 		if (sub->surface == view->surface)
 			wl_list_insert(compositor->view_list.prev, &view->link);
 		else
-			view_list_add_subsurface_view(compositor, sub, view);
+			view_list_add_subsurface_view(compositor, sub, view, output);
 	}
 }
 
 static void
-weston_compositor_build_view_list(struct weston_compositor *compositor)
+weston_compositor_build_view_list(struct weston_compositor *compositor,
+				  struct weston_output *output)
 {
 	struct weston_view *view, *tmp;
 	struct weston_layer *layer;
@@ -2684,7 +2771,7 @@ weston_compositor_build_view_list(struct weston_compositor *compositor)
 
 	wl_list_for_each(layer, &compositor->layer_list, link) {
 		wl_list_for_each(view, &layer->view_list.link, layer_link.link) {
-			view_list_add(compositor, view);
+			view_list_add(compositor, view, output);
 		}
 	}
 
@@ -2737,7 +2824,7 @@ weston_output_repaint(struct weston_output *output, void *repaint_data)
 	TL_POINT(ec, "core_repaint_begin", TLP_OUTPUT(output), TLP_END);
 
 	/* Rebuild the surface list and update surface transforms up front. */
-	weston_compositor_build_view_list(ec);
+	weston_compositor_build_view_list(ec, output);
 
 	/* Find the highest protection desired for an output */
 	wl_list_for_each(ev, &ec->view_list, link) {
@@ -6102,6 +6189,8 @@ weston_output_transform_coordinate(struct weston_output *output,
  *
  * The following happens:
  *
+ * - Destroys all paint nodes related to the output.
+ *
  * - The output assignments of all views in the current scenegraph are
  *   recomputed.
  *
@@ -6127,12 +6216,18 @@ static void
 weston_compositor_remove_output(struct weston_output *output)
 {
 	struct weston_compositor *compositor = output->compositor;
+	struct weston_paint_node *pnode, *pntmp;
 	struct weston_view *view;
 	struct weston_head *head;
 
 	assert(output->destroying);
 	assert(output->enabled);
 
+	wl_list_for_each_safe(pnode, pntmp,
+			      &output->paint_node_list, output_link) {
+		weston_paint_node_destroy(pnode);
+	}
+
 	wl_list_for_each(view, &compositor->view_list, link) {
 		if (view->output_mask & (1u << output->id))
 			weston_view_assign_output(view);
@@ -6483,6 +6578,7 @@ weston_output_enable(struct weston_output *output)
 
 	wl_list_init(&output->animation_list);
 	wl_list_init(&output->feedback_list);
+	wl_list_init(&output->paint_node_list);
 
 	/* Enable the output (set up the crtc or create a
 	 * window representing the output, set up the
@@ -6645,6 +6741,8 @@ weston_output_release(struct weston_output *output)
 	if (output->enabled)
 		weston_compositor_remove_output(output);
 
+	assert(wl_list_empty(&output->paint_node_list));
+
 	pixman_region32_fini(&output->region);
 	wl_list_remove(&output->link);
 

libweston/libweston-internal.h

@@ -1,7 +1,7 @@
 /*
  * Copyright © 2008-2011 Kristian Høgsberg
  * Copyright © 2017, 2018 General Electric Company
- * Copyright © 2012, 2017-2019 Collabora, Ltd.
+ * Copyright © 2012, 2017-2019, 2021 Collabora, Ltd.
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -40,6 +40,7 @@
  * features should either provide their own (internal) header or use this one.
  */
 
+#include <libweston/libweston.h>
 
 /* weston_buffer */
 
@@ -391,6 +392,29 @@ const uint64_t *
 weston_drm_format_get_modifiers(const struct weston_drm_format *format,
 				unsigned int *count_out);
 
+/**
+ * paint node
+ *
+ * A generic data structure unique for surface-view-output combination.
+ */
+struct weston_paint_node {
+	/* struct weston_surface::paint_node_list */
+	struct wl_list surface_link;
+	struct weston_surface *surface;
+
+	/* struct weston_view::paint_node_list */
+	struct wl_list view_link;
+	struct weston_view *view;
+
+	/* struct weston_output::paint_node_list */
+	struct wl_list output_link;
+	struct weston_output *output;
+};
+
+struct weston_paint_node *
+weston_view_find_paint_node(struct weston_view *view,
+			    struct weston_output *output);
+
 /* others */
 int
 wl_data_device_manager_init(struct wl_display *display);