[gtk/wip/chergert/glproto] add offscreen draw helper

[Christian Hergert <chergert src gnome org>]

commit d088c9a02d3ebd5b69cb37c8091ff52a97ed07e9
Author: Christian Hergert <chergert redhat com>
Date:   Sat Jan 2 23:16:04 2021 -0800

    add offscreen draw helper
    
    i find the struct approach much easier to reason about than the
    add_offscreen_ops() style even if it costs just a bit more setup
    to zero/flag fields. it also means we can do the whole thing with
    a single struct which based on what ive read on all the texturegion
    use cases, should be possible.

 gsk/next/gskglrenderjob.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)
---
diff --git a/gsk/next/gskglrenderjob.c b/gsk/next/gskglrenderjob.c
index 4ee60e3e70..f737480f7a 100644
--- a/gsk/next/gskglrenderjob.c
+++ b/gsk/next/gskglrenderjob.c
@@ -106,6 +106,8 @@ typedef struct _GskGLRenderOffscreen
   guint reset_clip : 1;
   guint do_not_cache : 1;
   guint linear_filter : 1;
+  guint flip_y : 1;
+  guint autorelease : 1;
 } GskGLRenderOffscreen;
 
 static void     gsk_gl_render_job_visit_node       (GskGLRenderJob       *job,
@@ -730,6 +732,52 @@ gsk_gl_render_job_draw (GskGLRenderJob *job,
   vertices[5].uv[1] = 0;
 }
 
+static void
+gsk_gl_render_job_draw_from_offscreen (GskGLRenderJob        *job,
+                                       const graphene_rect_t *bounds,
+                                       GskGLRenderOffscreen  *offscreen)
+{
+  GskGLDrawVertex *vertices;
+  float min_x = job->offset_x + bounds->origin.x;
+  float min_y = job->offset_y + bounds->origin.y;
+  float max_x = min_x + bounds->size.width;
+  float max_y = min_y + bounds->size.height;
+  float y1 = offscreen->flip_y ? offscreen->y2 : offscreen->y;
+  float y2 = offscreen->flip_y ? offscreen->y  : offscreen->y2;
+
+  vertices = gsk_gl_command_queue_add_vertices (job->command_queue, NULL);
+
+  vertices[0].position[0] = min_x;
+  vertices[0].position[1] = min_y;
+  vertices[0].uv[0] = offscreen->x;
+  vertices[0].uv[1] = y1;
+
+  vertices[1].position[0] = min_x;
+  vertices[1].position[1] = max_y;
+  vertices[1].uv[0] = offscreen->x;
+  vertices[1].uv[1] = y2;
+
+  vertices[2].position[0] = max_x;
+  vertices[2].position[1] = min_y;
+  vertices[2].uv[0] = offscreen->x2;
+  vertices[2].uv[1] = y1;
+
+  vertices[3].position[0] = max_x;
+  vertices[3].position[1] = max_y;
+  vertices[3].uv[0] = offscreen->x2;
+  vertices[3].uv[1] = y2;
+
+  vertices[4].position[0] = min_x;
+  vertices[4].position[1] = max_y;
+  vertices[4].uv[0] = offscreen->x;
+  vertices[4].uv[1] = y2;
+
+  vertices[5].position[0] = max_x;
+  vertices[5].position[1] = min_y;
+  vertices[5].uv[0] = offscreen->x2;
+  vertices[5].uv[1] = y1;
+}
+
 static void
 gsk_gl_render_job_visit_as_fallback (GskGLRenderJob *job,
                                      GskRenderNode  *node)
@@ -1412,10 +1460,12 @@ gsk_gl_render_job_visit_cross_fade_node (GskGLRenderJob *job,
   offscreen_start.force_offscreen = TRUE;
   offscreen_start.reset_clip = TRUE;
   offscreen_start.bounds = &node->bounds;
+  offscreen_start.autorelease = TRUE;
 
   offscreen_end.force_offscreen = TRUE;
   offscreen_end.reset_clip = TRUE;
   offscreen_end.bounds = &node->bounds;
+  offscreen_end.autorelease = TRUE;
 
   if (!gsk_gl_render_job_render_offscreen (job, start_node, &offscreen_start))
     {