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i965/blorp: Compute sample number correctly for 8x MSAA.

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When operating in persample dispatch mode, the blorp engine would
previously assume that subspan N always represented sample N (this is
correct assuming 4x MSAA and a 16-wide dispatch).  In order to support
8x MSAA, we must compute which sample is associated with each subspan,
using the "Starting Sample Pair Index" field in the thread payload.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
This commit is contained in:
Paul Berry
2012-07-17 21:06:01 -07:00
parent 082874e389
commit 619471dc32
1 changed files with 42 additions and 13 deletions
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src/mesa/drivers/dri/i965/brw_blorp_blit.cpp
+42 -13
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@@ -816,19 +816,48 @@ brw_blorp_blit_program::compute_frag_coords()
brw_ADD(&func, Y, stride(suboffset(R1, 5), 2, 4, 0), brw_imm_v(0x11001100));
if (key->persample_msaa_dispatch) {
/* The WM will be run in MSDISPMODE_PERSAMPLE with num_samples > 0.
* Therefore, subspan 0 will represent sample 0, subspan 1 will
* represent sample 1, and so on.
*
* So we need to populate S with the sequence (0, 0, 0, 0, 1, 1, 1, 1,
* 2, 2, 2, 2, 3, 3, 3, 3). The easiest way to do this is to populate a
* temporary variable with the sequence (0, 1, 2, 3), and then copy from
* it using vstride=1, width=4, hstride=0.
*
* TODO: implement the necessary calculation for 8x multisampling.
*/
brw_MOV(&func, t1, brw_imm_v(0x3210));
brw_MOV(&func, S, stride(t1, 1, 4, 0));
switch (key->rt_samples) {
case 4:
/* The WM will be run in MSDISPMODE_PERSAMPLE with num_samples == 4.
* Therefore, subspan 0 will represent sample 0, subspan 1 will
* represent sample 1, and so on.
*
* So we need to populate S with the sequence (0, 0, 0, 0, 1, 1, 1,
* 1, 2, 2, 2, 2, 3, 3, 3, 3). The easiest way to do this is to
* populate a temporary variable with the sequence (0, 1, 2, 3), and
* then copy from it using vstride=1, width=4, hstride=0.
*/
brw_MOV(&func, t1, brw_imm_v(0x3210));
brw_MOV(&func, S, stride(t1, 1, 4, 0));
break;
case 8: {
/* The WM will be run in MSDISPMODE_PERSAMPLE with num_samples == 8.
* Therefore, subspan 0 will represent sample N (where N is 0 or 4),
* subspan 1 will represent sample 1, and so on. We can find the
* value of N by looking at R0.0 bits 7:6 ("Starting Sample Pair
* Index") and multiplying by two (since samples are always delivered
* in pairs). That is, we compute 2*((R0.0 & 0xc0) >> 6) == (R0.0 &
* 0xc0) >> 5.
*
* Then we need to add N to the sequence (0, 0, 0, 0, 1, 1, 1, 1, 2,
* 2, 2, 2, 3, 3, 3, 3), which we compute by populating a temporary
* variable with the sequence (0, 1, 2, 3), and then reading from it
* using vstride=1, width=4, hstride=0.
*/
struct brw_reg t1_ud1 = vec1(retype(t1, BRW_REGISTER_TYPE_UD));
struct brw_reg r0_ud1 = vec1(retype(R0, BRW_REGISTER_TYPE_UD));
brw_AND(&func, t1_ud1, r0_ud1, brw_imm_ud(0xc0));
brw_SHR(&func, t1_ud1, t1_ud1, brw_imm_ud(5));
brw_MOV(&func, t2, brw_imm_v(0x3210));
brw_ADD(&func, S, retype(t1_ud1, BRW_REGISTER_TYPE_UW),
stride(t2, 1, 4, 0));
break;
}
default:
assert(!"Unrecognized sample count in "
"brw_blorp_blit_program::compute_frag_coords()");
break;
}
s_is_zero = false;
} else {
/* Either the destination surface is single-sampled, or the WM will be