i965: expose sample positions

Moves the definition of the sample positions out of
gen6_emit_3dstate_multisample, and unpacks them in
gen6_get_sample_position.

V2: Be consistent about `sample position` rather than `location`.

Signed-off-by: Chris Forbes <[email protected]>
Reviewed-by: Paul Berry <[email protected]>
Acked-by: Ian Romanick <[email protected]>

3 files changed, 82 insertions, 43 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_context.c b/src/mesa/drivers/dri/i965/brw_context.c
index 06d0da57200..a89ebb97aa6 100644
--- a/src/mesa/drivers/dri/i965/brw_context.c
+++ b/src/mesa/drivers/dri/i965/brw_context.c
@@ -95,6 +95,9 @@ static void brwInitDriverFunctions(struct intel_screen *screen,
       functions->EndTransformFeedback = gen7_end_transform_feedback;
    else
       functions->EndTransformFeedback = brw_end_transform_feedback;
+
+   if (screen->gen >= 6)
+      functions->GetSamplePosition = gen6_get_sample_position;
 }
 
 bool
diff --git a/src/mesa/drivers/dri/i965/brw_context.h b/src/mesa/drivers/dri/i965/brw_context.h
index 9758cfcf112..c974589b1e9 100644
--- a/src/mesa/drivers/dri/i965/brw_context.h
+++ b/src/mesa/drivers/dri/i965/brw_context.h
@@ -1230,6 +1230,11 @@ void
 gen6_emit_3dstate_sample_mask(struct brw_context *brw,
                               unsigned num_samples, float coverage,
                               bool coverage_invert, unsigned sample_mask);
+void
+gen6_get_sample_position(struct gl_context *ctx,
+                         struct gl_framebuffer *fb,
+                         GLuint index,
+                         GLfloat *result);
 
 /* gen7_urb.c */
 void
diff --git a/src/mesa/drivers/dri/i965/gen6_multisample_state.c b/src/mesa/drivers/dri/i965/gen6_multisample_state.c
index 844aad17bba..35071e846be 100644
--- a/src/mesa/drivers/dri/i965/gen6_multisample_state.c
+++ b/src/mesa/drivers/dri/i965/gen6_multisample_state.c
@@ -26,6 +26,77 @@
 #include "brw_context.h"
 #include "brw_defines.h"
 
+/* Sample positions:
+ *   2 6 a e
+ * 2   0
+ * 6       1
+ * a 2
+ * e     3
+ */
+static uint32_t
+sample_positions_4x[] = { 0xae2ae662 };
+/* Sample positions are based on a solution to the "8 queens" puzzle.
+ * Rationale: in a solution to the 8 queens puzzle, no two queens share
+ * a row, column, or diagonal.  This is a desirable property for samples
+ * in a multisampling pattern, because it ensures that the samples are
+ * relatively uniformly distributed through the pixel.
+ *
+ * There are several solutions to the 8 queens puzzle (see
+ * http://en.wikipedia.org/wiki/Eight_queens_puzzle).  This solution was
+ * chosen because it has a queen close to the center; this should
+ * improve the accuracy of centroid interpolation, since the hardware
+ * implements centroid interpolation by choosing the centermost sample
+ * that overlaps with the primitive being drawn.
+ *
+ * Note: from the Ivy Bridge PRM, Vol2 Part1 p304 (3DSTATE_MULTISAMPLE:
+ * Programming Notes):
+ *
+ *     "When programming the sample offsets (for NUMSAMPLES_4 or _8 and
+ *     MSRASTMODE_xxx_PATTERN), the order of the samples 0 to 3 (or 7
+ *     for 8X) must have monotonically increasing distance from the
+ *     pixel center. This is required to get the correct centroid
+ *     computation in the device."
+ *
+ * Sample positions:
+ *   1 3 5 7 9 b d f
+ * 1     5
+ * 3           2
+ * 5               6
+ * 7 4
+ * 9       0
+ * b             3
+ * d         1
+ * f   7
+ */
+static uint32_t
+sample_positions_8x[] = { 0xdbb39d79, 0x3ff55117 };
+
+
+void
+gen6_get_sample_position(struct gl_context *ctx,
+                         struct gl_framebuffer *fb,
+                         GLuint index, GLfloat *result)
+{
+   switch (fb->Visual.samples) {
+   case 1:
+      result[0] = result[1] = 0.5f;
+      break;
+   case 4: {
+      uint8_t val = (uint8_t)(sample_positions_4x[0] >> (8*index));
+      result[0] = (val & 0xf) / 16.0f;
+      result[1] = ((val >> 4) & 0xf) / 16.0f;
+      break;
+   }
+   case 8: {
+      uint8_t val = (uint8_t)(sample_positions_8x[index>>2] >> (8*(index & 3)));
+      result[0] = (val & 0xf) / 16.0f;
+      result[1] = ((val >> 4) & 0xf) / 16.0f;
+      break;
+   }
+   default:
+      assert(!"Not implemented");
+   }
+}
 
 /**
  * 3DSTATE_MULTISAMPLE
@@ -47,52 +118,12 @@ gen6_emit_3dstate_multisample(struct brw_context *brw,
       break;
    case 4:
       number_of_multisamples = MS_NUMSAMPLES_4;
-      /* Sample positions:
-       *   2 6 a e
-       * 2   0
-       * 6       1
-       * a 2
-       * e     3
-       */
-      sample_positions_3210 = 0xae2ae662;
+      sample_positions_3210 = sample_positions_4x[0];
       break;
    case 8:
       number_of_multisamples = MS_NUMSAMPLES_8;
-      /* Sample positions are based on a solution to the "8 queens" puzzle.
-       * Rationale: in a solution to the 8 queens puzzle, no two queens share
-       * a row, column, or diagonal.  This is a desirable property for samples
-       * in a multisampling pattern, because it ensures that the samples are
-       * relatively uniformly distributed through the pixel.
-       *
-       * There are several solutions to the 8 queens puzzle (see
-       * http://en.wikipedia.org/wiki/Eight_queens_puzzle).  This solution was
-       * chosen because it has a queen close to the center; this should
-       * improve the accuracy of centroid interpolation, since the hardware
-       * implements centroid interpolation by choosing the centermost sample
-       * that overlaps with the primitive being drawn.
-       *
-       * Note: from the Ivy Bridge PRM, Vol2 Part1 p304 (3DSTATE_MULTISAMPLE:
-       * Programming Notes):
-       *
-       *     "When programming the sample offsets (for NUMSAMPLES_4 or _8 and
-       *     MSRASTMODE_xxx_PATTERN), the order of the samples 0 to 3 (or 7
-       *     for 8X) must have monotonically increasing distance from the
-       *     pixel center. This is required to get the correct centroid
-       *     computation in the device."
-       *
-       * Sample positions:
-       *   1 3 5 7 9 b d f
-       * 1     5
-       * 3           2
-       * 5               6
-       * 7 4
-       * 9       0
-       * b             3
-       * d         1
-       * f   7
-       */
-      sample_positions_3210 = 0xdbb39d79;
-      sample_positions_7654 = 0x3ff55117;
+      sample_positions_3210 = sample_positions_8x[0];
+      sample_positions_7654 = sample_positions_8x[1];
       break;
    default:
       assert(!"Unrecognized num_samples in gen6_emit_3dstate_multisample");