[Glamor] [PATCH 2/2] Use CLAMP_TO_BORDER in copy_n_to_n so we can sample outside of the source

[Chris Wilson]

In order to reduce a composite operation to a source, we need to provide
Render semantics for the pixel values of samples outside of the source
pixmap, i.e. they need to be rgba(0, 0, 0, 0). This is provided by using
the CLAMP_TO_BORDER repeat mode, but only if the texture has an alpha
channel.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 src/glamor_copyarea.c |    6 ++++++
 src/glamor_render.c   |   28 +++++++++++++++-------------
 2 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/src/glamor_copyarea.c b/src/glamor_copyarea.c
index a39c970..f2d710a 100644
--- a/src/glamor_copyarea.c
+++ b/src/glamor_copyarea.c
@@ -226,6 +226,12 @@ glamor_copy_n_to_n_textured(DrawablePtr src,
 		dispatch->glTexParameteri(GL_TEXTURE_2D,
 					  GL_TEXTURE_MAG_FILTER,
 					  GL_NEAREST);
+		dispatch->glTexParameteri(GL_TEXTURE_2D,
+					  GL_TEXTURE_WRAP_S,
+					  GL_CLAMP_TO_BORDER);
+		dispatch->glTexParameteri(GL_TEXTURE_2D,
+					  GL_TEXTURE_WRAP_T,
+					  GL_CLAMP_TO_BORDER);
 
 		dispatch->glVertexAttribPointer(GLAMOR_VERTEX_SOURCE, 2,
 						GL_FLOAT, GL_FALSE,
diff --git a/src/glamor_render.c b/src/glamor_render.c
index b70ace2..04eb0b2 100644
--- a/src/glamor_render.c
+++ b/src/glamor_render.c
@@ -622,19 +622,21 @@ glamor_composite_with_copy(CARD8 op,
 				      x_source, y_source,
 				      0, 0, x_dest, y_dest, width, height))
 		return TRUE;
-	/* Fallback if we sample outside the source so that we swizzle the
-	 * clear color appropriately. If the source has an alpha channel,
-	 * we could rely on CLAMP_TO_BORDER working as required...
-	 */
-	if (region.extents.x1 + x_source - x_dest < 0)
-		goto cleanup_region;
-	if (region.extents.x2 + x_source - x_dest > source->pDrawable->width)
-		goto cleanup_region;
-
-	if (region.extents.y1 + y_source - y_dest < 0)
-		goto cleanup_region;
-	if (region.extents.y2 + y_source - y_dest > source->pDrawable->height)
-		goto cleanup_region;
+
+	if (PICT_FORMAT_A(source->format) == 0) {
+		/* Fallback if we sample outside the source so that we
+		 * swizzle the correct clear color for out-of-bounds texels.
+		 */
+		if (region.extents.x1 + x_source - x_dest < 0)
+			goto cleanup_region;
+		if (region.extents.x2 + x_source - x_dest > source->pDrawable->width)
+			goto cleanup_region;
+
+		if (region.extents.y1 + y_source - y_dest < 0)
+			goto cleanup_region;
+		if (region.extents.y2 + y_source - y_dest > source->pDrawable->height)
+			goto cleanup_region;
+	}
 
 	ret = glamor_copy_n_to_n_nf(source->pDrawable,
 				    dest->pDrawable, NULL,
-- 
1.7.8.3