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ir3: Clarify what's happening in the interpolateAtOffset() math.

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nir_builder lets us build much cleaner code than we had (assuming that we
get a scalarizing after this).

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17322>
This commit is contained in:
Emma Anholt 2022-07-05 10:15:07 -07:00 • committed by Marge Bot
parent 240a98297d
commit c5eb7ef246
1 changed files with 16 additions and 36 deletions
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52
src/freedreno/ir3/ir3_nir_lower_load_barycentric_at_offset.c
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@ -29,16 +29,6 @@
* instructions.
*/
static nir_ssa_def *
load(nir_builder *b, unsigned ncomp, nir_intrinsic_op op)
{
nir_intrinsic_instr *load_size = nir_intrinsic_instr_create(b->shader, op);
nir_ssa_dest_init(&load_size->instr, &load_size->dest, ncomp, 32, NULL);
nir_builder_instr_insert(b, &load_size->instr);
return &load_size->dest.ssa;
}
static nir_ssa_def *
ir3_nir_lower_load_barycentric_at_offset_instr(nir_builder *b, nir_instr *instr,
void *data)
@ -52,38 +42,28 @@ ir3_nir_lower_load_barycentric_at_offset_instr(nir_builder *b, nir_instr *instr,
/* note: at_offset is defined to be relative to the center of the pixel */
nir_ssa_def *ij = nir_load_barycentric_pixel(b, 32, .interp_mode = interp_mode);
nir_ssa_def *s = load(b, 1, nir_intrinsic_load_persp_center_rhw_ir3);
s = nir_frcp(b, s);
/* scaled ij with s as 3rd component: */
nir_ssa_def *sij =
nir_vec3(b, nir_fmul(b, chan(ij, 0), s), nir_fmul(b, chan(ij, 1), s), s);
nir_ssa_def *foo = nir_fddx(b, sij);
nir_ssa_def *bar = nir_fddy(b, sij);
/* Need helper invocations for our ddx/ddys to work. */
if (b->shader->info.stage == MESA_SHADER_FRAGMENT)
b->shader->info.fs.needs_quad_helper_invocations = true;
nir_ssa_def *x, *y, *z, *i, *j;
nir_ssa_def *center_w = nir_frcp(b, nir_load_persp_center_rhw_ir3(b, 32));
x = nir_ffma(b, chan(off, 0), chan(foo, 0), chan(sij, 0));
y = nir_ffma(b, chan(off, 0), chan(foo, 1), chan(sij, 1));
z = nir_ffma(b, chan(off, 0), chan(foo, 2), chan(sij, 2));
/* scaled ij -- ij comes in multiplied by by 1/center_w so multiply that back
* out, plus add center_w as the 3rd component for taking the derivatives.
*
* We actually suspect that we should be using rhw here instead of center_w,
* but no tests seem to distinguish between the two.
*/
nir_ssa_def *sij =
nir_vec3(b, nir_fmul(b, chan(ij, 0), center_w), nir_fmul(b, chan(ij, 1), center_w), center_w);
x = nir_ffma(b, chan(off, 1), chan(bar, 0), x);
y = nir_ffma(b, chan(off, 1), chan(bar, 1), y);
z = nir_ffma(b, chan(off, 1), chan(bar, 2), z);
/* Get the offset value from pixel center for ij, and also for w. */
nir_ssa_def *pos = sij;
pos = nir_ffma(b, chan(off, 0), nir_fddx(b, sij), pos);
pos = nir_ffma(b, chan(off, 1), nir_fddy(b, sij), pos);
/* convert back into primitive space: */
z = nir_frcp(b, z);
i = nir_fmul(b, z, x);
j = nir_fmul(b, z, y);
ij = nir_vec2(b, i, j);
return ij;
/* convert back into screen space, dividing by the offset 1/w */
return nir_fmul(b, nir_channels(b, pos, 0x3), nir_frcp(b, chan(pos, 2)));
}
static bool