[Mesa-dev] [PATCH] meta: Fix blitting a framebuffer with renderbuffer attachment

[Anuj Phogat]

This patch fixes a case of framebuffer blitting with renderbuffer
as color attachment and GL_LINEAR filter. Meta implementation of
glBlitFrambuffer() converts source color buffer to a texture and
uses it to do the scaled blitting in to destination buffer. Using
the exact source rectangle to create the texture does incorrect
linear filtering along the edges. This patch makes the changes to
extend the texture edges by one pixel in x, y directions. This
ensures correct linear filtering.

It fixes failing piglit fbo-linear-blit test. Patch for the testcase
is on piglit mailing list.

Signed-off-by: Anuj Phogat <anuj.phogat at gmail.com>
---
 src/mesa/drivers/common/meta.c | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/src/mesa/drivers/common/meta.c b/src/mesa/drivers/common/meta.c
index c62927c..155c4fa 100644
--- a/src/mesa/drivers/common/meta.c
+++ b/src/mesa/drivers/common/meta.c
@@ -1879,19 +1879,24 @@ _mesa_meta_BlitFramebuffer(struct gl_context *ctx,
       const GLenum rb_base_format =
          _mesa_base_tex_format(ctx, colorReadRb->InternalFormat);
 
-      newTex = alloc_texture(tex, srcW, srcH, rb_base_format);
-      setup_copypix_texture(ctx, tex, newTex, srcX, srcY, srcW, srcH,
+      /* Using  the exact source rectangle to create the texture does incorrect
+       * linear filtering along the edges. So, allocate the texture extended along
+       * edges by one pixel in x, y directions.
+       */
+      newTex = alloc_texture(tex, srcW + 2, srcH + 2, rb_base_format);
+      setup_copypix_texture(ctx, tex, newTex,
+                            srcX - 1, srcY - 1, srcW + 2, srcH + 2,
                             rb_base_format, filter);
       /* texcoords (after texture allocation!) */
       {
-         verts[0].s = 0.0F;
-         verts[0].t = 0.0F;
-         verts[1].s = tex->Sright;
-         verts[1].t = 0.0F;
-         verts[2].s = tex->Sright;
-         verts[2].t = tex->Ttop;
-         verts[3].s = 0.0F;
-         verts[3].t = tex->Ttop;
+         verts[0].s = 1.0F;
+         verts[0].t = 1.0F;
+         verts[1].s = tex->Sright - 1.0F;
+         verts[1].t = 1.0F;
+         verts[2].s = tex->Sright - 1.0F;
+         verts[2].t = tex->Ttop - 1.0F;
+         verts[3].s = 1.0F;
+         verts[3].t = tex->Ttop - 1.0F;
 
          /* upload new vertex data */
          _mesa_BufferSubData(GL_ARRAY_BUFFER_ARB, 0, sizeof(verts), verts);
-- 
1.8.1.4