[Mesa-dev] [PATCH 04/12] mesa: Add a helper function _mesa_get_min_invocations_per_fragment()

[Anuj Phogat]

Thsi function is used to test if we need to do per sample shading or
per fragment shading.

Signed-off-by: Anuj Phogat <anuj.phogat at gmail.com>
---
 src/mesa/program/program.c | 31 +++++++++++++++++++++++++++++++
 src/mesa/program/program.h |  3 +++
 2 files changed, 34 insertions(+)

diff --git a/src/mesa/program/program.c b/src/mesa/program/program.c
index 093d372..e12e6ec 100644
--- a/src/mesa/program/program.c
+++ b/src/mesa/program/program.c
@@ -1024,3 +1024,34 @@ _mesa_postprocess_program(struct gl_context *ctx, struct gl_program *prog)
 
    }
 }
+
+/* Gets the minimum number of shader invocations per fragment.
+ * This function is useful to determine if we need to do per
+ * sample shading or per fragment shading.
+ */
+GLint
+_mesa_get_min_invocations_per_fragment(struct gl_context *ctx,
+                                       const struct gl_fragment_program *prog)
+{
+   /* From ARB_sample_shading specification:
+    * "Using gl_SampleID in a fragment shader causes the entire shader
+    *  to be evaluated per-sample."
+    *
+    * "Using gl_SamplePosition in a fragment shader causes the entire
+    *  shader to be evaluated per-sample."
+    *
+    * "If MULTISAMPLE or SAMPLE_SHADING_ARB is disabled, sample shading
+    *  has no effect."
+    */
+   if (ctx->Multisample.Enabled) {
+      if (prog->Base.SystemValuesRead & SYSTEM_BIT_SAMPLE_ID ||
+          prog->Base.SystemValuesRead & SYSTEM_BIT_SAMPLE_POS)
+         return ctx->DrawBuffer->Visual.samples;
+      else if (ctx->Multisample.SampleShading)
+         return ceil(ctx->Multisample.MinSampleShadingValue *
+                     ctx->DrawBuffer->Visual.samples);
+      else
+         return 1;
+   }
+   return 1;
+}
diff --git a/src/mesa/program/program.h b/src/mesa/program/program.h
index 34965ab..353ccab 100644
--- a/src/mesa/program/program.h
+++ b/src/mesa/program/program.h
@@ -187,6 +187,9 @@ _mesa_valid_register_index(const struct gl_context *ctx,
 extern void
 _mesa_postprocess_program(struct gl_context *ctx, struct gl_program *prog);
 
+extern GLint
+_mesa_get_min_invocations_per_fragment(struct gl_context *ctx,
+                                       const struct gl_fragment_program *prog);
 
 static inline GLuint
 _mesa_program_target_to_index(GLenum v)
-- 
1.8.1.4