radeonsi: use better sample locations for 4x MSAA

Discovered by luck. Verified with the piglit MSAA accuracy test.
It also shows that the worst case EQAA 16s4f results in very good 4x MSAA
in the worst case.

Nine might not like these positions, but they are prettier to the eye and
GL doesn't care.

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>

diff --git a/src/gallium/drivers/radeonsi/si_state_msaa.c b/src/gallium/drivers/radeonsi/si_state_msaa.c
index 0f9e0fe..b6504d5 100644 (file)
--- a/src/gallium/drivers/radeonsi/si_state_msaa.c
+++ b/src/gallium/drivers/radeonsi/si_state_msaa.c
@@ -92,11 +92,6 @@ static const uint32_t sample_locs_2x =
        FILL_SREG(-4,-4,   4, 4,   0, 0,   0, 0); /* S2 & S3 fields are not used by 2x MSAA */
 static const uint64_t centroid_priority_2x = 0x1010101010101010ull;
 
-/* 4x MSAA */
-static const uint32_t sample_locs_4x =
-       FILL_SREG(-2,-6,   2, 6,  -6, 2,   6,-2);
-static const uint64_t centroid_priority_4x = 0x3210321032103210ull;
-
 /* 8x MSAA */
 static const uint32_t sample_locs_8x[] = {
        FILL_SREG(-3,-5,   5, 1,  -5, 5,   7,-7),
@@ -106,13 +101,17 @@ static const uint32_t sample_locs_8x[] = {
 };
 static const uint64_t centroid_priority_8x = 0x3542017635420176ull;
 
-/* 16x MSAA */
-static const uint32_t sample_locs_16x[] = {
+/* 4x and 16x MSAA
+ * (the first 4 locations happen to be optimal for 4x MSAA, better than
+ *  the standard DX 4x locations)
+ */
+static const uint32_t sample_locs_4x_16x[] = {
        FILL_SREG(-5,-2,   5, 3,  -2, 6,   3,-5),
        FILL_SREG(-7,-8,   1, 1,  -6, 4,   7,-4),
        FILL_SREG(-1,-3,   6, 7,  -3, 2,   0,-7),
        FILL_SREG(-4,-6,   2, 5,  -8, 0,   4,-1),
 };
+static const uint64_t centroid_priority_4x = 0x2310231023102310ull;
 static const uint64_t centroid_priority_16x = 0x497ec6b231d0fa85ull;
 
 static void si_get_sample_position(struct pipe_context *ctx, unsigned sample_count,
@@ -129,13 +128,13 @@ static void si_get_sample_position(struct pipe_context *ctx, unsigned sample_cou
                sample_locs = &sample_locs_2x;
                break;
        case 4:
-               sample_locs = &sample_locs_4x;
+               sample_locs = sample_locs_4x_16x;
                break;
        case 8:
                sample_locs = sample_locs_8x;
                break;
        case 16:
-               sample_locs = sample_locs_16x;
+               sample_locs = sample_locs_4x_16x;
                break;
        }
 
@@ -183,13 +182,13 @@ void si_emit_sample_locations(struct radeon_winsys_cs *cs, int nr_samples)
                si_emit_max_4_sample_locs(cs, centroid_priority_2x, sample_locs_2x);
                break;
        case 4:
-               si_emit_max_4_sample_locs(cs, centroid_priority_4x, sample_locs_4x);
+               si_emit_max_4_sample_locs(cs, centroid_priority_4x, sample_locs_4x_16x[0]);
                break;
        case 8:
                si_emit_max_16_sample_locs(cs, centroid_priority_8x, sample_locs_8x, 8);
                break;
        case 16:
-               si_emit_max_16_sample_locs(cs, centroid_priority_16x, sample_locs_16x, 16);
+               si_emit_max_16_sample_locs(cs, centroid_priority_16x, sample_locs_4x_16x, 16);
                break;
        }
 }