[cairo] [PATCH 3/3] gl/msaa: Scissor simple rectangular clips

[Martin Robinson]

Instead of using the stencil buffer to perform simple
rectangular clips, just scissor the clip rectangle.
---
 src/cairo-gl-msaa-compositor.c |   68 ++++++++++++++++++++++++++++++---------
 1 files changed, 52 insertions(+), 16 deletions(-)

diff --git a/src/cairo-gl-msaa-compositor.c b/src/cairo-gl-msaa-compositor.c
index fdd9666..8a1e55d 100644
--- a/src/cairo-gl-msaa-compositor.c
+++ b/src/cairo-gl-msaa-compositor.c
@@ -210,6 +210,49 @@ _draw_clip_to_stencil_buffer (cairo_gl_context_t	*ctx,
     return status;;
 }
 
+static void
+_scissor_to_box (cairo_gl_surface_t	*surface,
+		 const cairo_box_t	*box)
+{
+    double x = _cairo_fixed_to_double (box->p1.x);
+    double y = _cairo_fixed_to_double (box->p1.y);
+    double width = _cairo_fixed_to_double (box->p2.x) - x;
+    double height = _cairo_fixed_to_double (box->p2.y) - y;
+
+    if (_cairo_gl_surface_is_texture (surface) == FALSE)
+	y = surface->height - (y + height);
+    glScissor (x, y, width, height);
+    glEnable (GL_SCISSOR_TEST);
+}
+
+static cairo_int_status_t
+_scissor_and_clip (cairo_gl_context_t		*ctx,
+		   cairo_gl_composite_t		*setup,
+		   cairo_composite_rectangles_t	*composite,
+		   cairo_bool_t			*used_stencil_buffer)
+{
+    cairo_rectangle_int_t *bounds = &composite->unbounded;
+    cairo_clip_t *clip = composite->clip;
+
+    cairo_gl_surface_t *dst = (cairo_gl_surface_t *) composite->surface;
+    *used_stencil_buffer = FALSE;
+
+    if (_cairo_composite_rectangles_can_reduce_clip (composite, clip)) {
+	_scissor_to_rectangle (dst, bounds);
+	return CAIRO_INT_STATUS_SUCCESS;
+    }
+
+    /* If we cannot reduce the clip to a rectangular region,
+       we scissor and clip using the stencil buffer */
+    if (clip->num_boxes > 1 || clip->path != NULL) {
+	*used_stencil_buffer = TRUE;
+	_scissor_to_rectangle (dst, bounds);
+	return _draw_clip_to_stencil_buffer (ctx, setup, clip);
+    }
+
+    _scissor_to_box (dst, clip->boxes);
+    return CAIRO_INT_STATUS_SUCCESS;
+}
 static cairo_int_status_t
 _cairo_gl_msaa_compositor_paint (const cairo_compositor_t	*compositor,
 				 cairo_composite_rectangles_t	*composite)
@@ -303,14 +346,10 @@ _cairo_gl_msaa_compositor_stroke (const cairo_compositor_t	*compositor,
     if (unlikely (status))
 	goto finish;
 
-    _scissor_to_rectangle (dst, &composite->unbounded);
-    if (! _cairo_composite_rectangles_can_reduce_clip (composite,
-						       composite->clip))
-    {
-	status = _draw_clip_to_stencil_buffer (info.ctx, &info.setup, composite->clip);
-	if (unlikely (status))
-	    goto finish;
-    }
+    status = _scissor_and_clip (info.ctx, &info.setup, composite,
+				&used_stencil_buffer_for_clip);
+    if (unlikely (status))
+	goto finish;
 
     status = _cairo_path_fixed_stroke_to_shaper ((cairo_path_fixed_t *) path,
 						 style,
@@ -351,6 +390,7 @@ _cairo_gl_msaa_compositor_fill (const cairo_compositor_t	*compositor,
     cairo_gl_context_t *ctx = NULL;
     cairo_int_status_t status;
     cairo_traps_t traps;
+    cairo_bool_t used_stencil_buffer;
 
     if (antialias != CAIRO_ANTIALIAS_NONE)
 	return CAIRO_INT_STATUS_UNSUPPORTED;
@@ -379,14 +419,10 @@ _cairo_gl_msaa_compositor_fill (const cairo_compositor_t	*compositor,
     if (unlikely (status))
 	goto cleanup_setup;
 
-    _scissor_to_rectangle (dst, &composite->unbounded);
-    if (! _cairo_composite_rectangles_can_reduce_clip (composite,
-						       composite->clip))
-    {
-	status = _draw_clip_to_stencil_buffer (ctx, &setup, composite->clip);
-	if (unlikely (status))
-	    goto cleanup_setup;
-    }
+    status = _scissor_and_clip (ctx, &setup, composite,
+				&used_stencil_buffer);
+    if (unlikely (status))
+	goto cleanup_setup;
 
     status = _draw_traps (ctx, &setup, &traps);
     if (unlikely (status))
-- 
1.7.5.4