From f0be8d94a51d9562a9fe9958d738f427b1bdd3d4 Mon Sep 17 00:00:00 2001
From: Daniel Stone <daniels@collabora.com>
Date: Fri, 3 Oct 2025 00:29:07 +0200
Subject: [PATCH] gl-renderer: Use glClear for solid opaque regions

If we have a solid region which is opaque, we don't need to go through
blending: we can simply emit a glClear, which has a pretty big benefit
on tilers in particular.

Signed-off-by: Daniel Stone <daniels@collabora.com>
---
 libweston/renderer-gl/gl-renderer.c | 38 +++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/libweston/renderer-gl/gl-renderer.c b/libweston/renderer-gl/gl-renderer.c
index d81f28d52..ef9b792e5 100644
--- a/libweston/renderer-gl/gl-renderer.c
+++ b/libweston/renderer-gl/gl-renderer.c
@@ -2011,6 +2011,37 @@ repaint_region(struct gl_renderer *gr,
 		gr->barycentric_stream.size = 0;
 }
 
+static void
+clear_region(struct gl_renderer *gr, struct weston_paint_node *pnode,
+	     pixman_region32_t *repaint)
+{
+	struct weston_output *output = pnode->output;
+	struct gl_output_state *go = get_output_state(pnode->output);
+	EGLint *rects;
+	EGLint nrects;
+	int i;
+
+	pixman_region_to_egl(output, repaint, go->border_status,
+			     &rects, &nrects);
+	assert(nrects > 0);
+
+	/* We must be either fully transparent - punching a hole for an
+	 * underlay - or fully opaque, to use clear rather than blending. */
+	assert(pnode->solid.a == 0.0f || pnode->solid.a == 1.0f);
+	set_blend_state(gr, false);
+	glClearColor(pnode->solid.r, pnode->solid.g, pnode->solid.b,
+		     pnode->solid.a);
+
+	glEnable(GL_SCISSOR_TEST);
+	for (i = 0; i < nrects; i++) {
+		EGLint *r = &rects[i * 4];
+		glScissor(r[0], r[1], r[2], r[3]);
+		glClear(GL_COLOR_BUFFER_BIT);
+	}
+	glDisable(GL_SCISSOR_TEST);
+	free(rects);
+}
+
 static void
 draw_paint_node(struct weston_paint_node *pnode,
 		pixman_region32_t *damage /* in global coordinates */)
@@ -2045,6 +2076,13 @@ draw_paint_node(struct weston_paint_node *pnode,
 		goto out;
 	}
 
+	if (!gr->debug_mode && pnode->draw_solid && pnode->is_fully_opaque &&
+	    pnode->view->alpha == 1.0f && !pnode->surf_xform.transform) {
+		clear_region(gr, pnode, &repaint);
+		gs->used_in_output_repaint = true;
+		goto out;
+	}
+
 	if (ensure_surface_buffer_is_ready(gr, gs, pnode) < 0)
 		goto out;