ngl: Optimize underlines in text

Opportunistically use the coloring program for
drawing underlines instead of the color program.
This avoids program changes in the middle of
text.

For the Emoji text scrolling benchmark, this reduces
the program changes per frame from > 1000 to around 100.

diff --git a/gsk/ngl/gsknglrenderjob.c b/gsk/ngl/gsknglrenderjob.c
index b1bda44790d239f9caac80dd23ef72d78f420c15..69c92ac80f8d8fbff4f16e61e3888ecaf8df9af7 100644 (file)
--- a/gsk/ngl/gsknglrenderjob.c
+++ b/gsk/ngl/gsknglrenderjob.c
@@ -1360,16 +1360,54 @@ blur_node (GskNglRenderJob       *job,
   *max_y = job->offset_y + node->bounds.origin.y + node->bounds.size.height + half_blur_extra;
 }
 
+#define ATLAS_SIZE 512
+
 static inline void
 gsk_ngl_render_job_visit_color_node (GskNglRenderJob     *job,
                                      const GskRenderNode *node)
 {
   guint16 color[4];
+  GskNglProgram *program;
+  GskNglCommandBatch *batch;
 
   rgba_to_half (gsk_color_node_get_color (node), color);
-  gsk_ngl_render_job_begin_draw (job, CHOOSE_PROGRAM (job, color));
-  gsk_ngl_render_job_draw_rect_with_color (job, &node->bounds, color);
-  gsk_ngl_render_job_end_draw (job);
+
+  /* Avoid switching away from the coloring program for
+   * rendering a solid color.
+   */
+  program = CHOOSE_PROGRAM (job, coloring);
+  batch = gsk_ngl_command_queue_get_batch (job->command_queue);
+
+  if (batch->any.kind == GSK_NGL_COMMAND_KIND_DRAW &&
+      batch->any.program == program->id)
+    {
+      GskNglRenderOffscreen offscreen = {0};
+
+      gsk_ngl_render_job_begin_draw (job, program);
+
+      /* The top left few pixels in our atlases are always
+       * solid white, so we can use it here, without
+       * having to choose any particular atlas texture.
+       */
+      offscreen.was_offscreen = FALSE;
+      offscreen.area.x = 1.f / ATLAS_SIZE;
+      offscreen.area.y = 1.f / ATLAS_SIZE;
+      offscreen.area.x2 = 2.f / ATLAS_SIZE;
+      offscreen.area.y2 = 2.f / ATLAS_SIZE;
+
+      gsk_ngl_render_job_draw_offscreen_with_color (job,
+                                                    &node->bounds,
+                                                    &offscreen,
+                                                    color);
+
+      gsk_ngl_render_job_end_draw (job);
+    }
+  else
+    {
+      gsk_ngl_render_job_begin_draw (job, CHOOSE_PROGRAM (job, color));
+      gsk_ngl_render_job_draw_rect_with_color (job, &node->bounds, color);
+      gsk_ngl_render_job_end_draw (job);
+    }
 }
 
 static inline void