nir/lower_tex: Fix minor error in YUV color conversion matrix

The matrix used for YCbCr to RGB is listed in:

    https://en.wikipedia.org/wiki/YCbCr

There was an error in converting the offsets from integers to unorm
values: 0.0625=16/256 should be 16.0/255,and 0.5=128.0/256 should be
128.0/255.  With this fix, the CSC result is bit aligned with wikipedia's
conversion result and FFMPeg's result.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100854
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>

diff --git a/src/compiler/nir/nir_lower_tex.c b/src/compiler/nir/nir_lower_tex.c
index 352d1499bc8d3a949e8f00dc33a69baa66d830ac..4ef81955513e6d6ac82894da7ccad0f608e3eb2e 100644 (file)
--- a/src/compiler/nir/nir_lower_tex.c
+++ b/src/compiler/nir/nir_lower_tex.c
@@ -244,9 +244,9 @@ convert_yuv_to_rgb(nir_builder *b, nir_tex_instr *tex,
    nir_ssa_def *yuv =
       nir_vec4(b,
                nir_fmul(b, nir_imm_float(b, 1.16438356f),
-                        nir_fadd(b, y, nir_imm_float(b, -0.0625f))),
-               nir_channel(b, nir_fadd(b, u, nir_imm_float(b, -0.5f)), 0),
-               nir_channel(b, nir_fadd(b, v, nir_imm_float(b, -0.5f)), 0),
+                        nir_fadd(b, y, nir_imm_float(b, -16.0f / 255.0f))),
+               nir_channel(b, nir_fadd(b, u, nir_imm_float(b, -128.0f / 255.0f)), 0),
+               nir_channel(b, nir_fadd(b, v, nir_imm_float(b, -128.0f / 255.0f)), 0),
                nir_imm_float(b, 0.0));
 
    nir_ssa_def *red = nir_fdot4(b, yuv, nir_build_imm(b, 4, 32, m[0]));