diff options
authorAnuj Phogat <>2014-01-15 10:23:02 -0800
committerAnuj Phogat <>2014-01-21 14:42:28 -0800
commitf5cfb4ae21df8eebfc6b86c0ce858b1c0a9160dd (patch)
parenta92e5f7cf63d496ad7830b5cea4bbab287c25b8e (diff)
i965: Ignore 'centroid' interpolation qualifier in case of persample shading
This patch handles the use of 'centroid' qualifier with 'in' variables in a fragment shader when persample shading is enabled. Per sample shading for the whole fragment shader can be enabled by: glEnable(GL_SAMPLE_SHADING) or using {gl_SamplePosition, gl_SampleID} builtin variables in fragment shader. Explaining it below in more detail. /* Enable sample shading using OpenGL API */ glEnable(GL_SAMPLE_SHADING); glMinSampleShading(1.0); Example fragment shader: in vec4 a; centroid in vec4 b; main() { ... } Variable 'a' will be interpolated at sample location. But, what interpolation should we use for variable 'b' ? ARB_sample_shading recommends interpolation at sample position for all the variables. GLSL 400 (and earlier) spec says that: "When an interpolation qualifier is used, it overrides settings established through the OpenGL API." But, this text got deleted in later versions of GLSL. NVIDIA's and AMD's proprietary linux drivers (at OpenGL 4.3) interpolates at sample position. This convinces me to use the similar approach on intel hardware. Cc: Signed-off-by: Anuj Phogat <> Reviewed-by: Chris Forbes <>
1 files changed, 1 insertions, 1 deletions
diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index 430a530d242..a0e48305080 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -1089,7 +1089,7 @@ fs_visitor::emit_general_interpolation(ir_variable *ir)
struct brw_reg interp = interp_reg(location, k);
emit_linterp(attr, fs_reg(interp), interpolation_mode,
- ir->data.centroid,
+ ir->data.centroid && !c->key.persample_shading,
ir->data.sample || c->key.persample_shading);
if (brw->needs_unlit_centroid_workaround && ir->data.centroid) {
/* Get the pixel/sample mask into f0 so that we know