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-rw-r--r--src/mesa/program/program.c32
1 files changed, 32 insertions, 0 deletions
diff --git a/src/mesa/program/program.c b/src/mesa/program/program.c
index 093d37297b4..a102ec17ab4 100644
--- a/src/mesa/program/program.c
+++ b/src/mesa/program/program.c
@@ -32,6 +32,7 @@
#include "main/glheader.h"
#include "main/context.h"
#include "main/hash.h"
+#include "main/macros.h"
#include "program.h"
#include "prog_cache.h"
#include "prog_parameter.h"
@@ -1024,3 +1025,34 @@ _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 |
+ SYSTEM_BIT_SAMPLE_POS))
+ return MAX2(ctx->DrawBuffer->Visual.samples, 1);
+ else if (ctx->Multisample.SampleShading)
+ return MAX2(ceil(ctx->Multisample.MinSampleShadingValue *
+ ctx->DrawBuffer->Visual.samples), 1);
+ else
+ return 1;
+ }
+ return 1;
+}