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nv2a: More accurate handling of exceptional fog values in VSH

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The handling of infinite fog coordinates in #660 does not exactly
match HW behavior for all bias and multiplier values. Further testing
indicates that the handling of the infinite value appears to override
all combinations of FOG_PARAM bias/multipliers, rather than keeping
the bias. This change emulates this behavior and also fixes NaN
handling, which similarly seems to be fog-mode dependent.

Fixes #2474
Fixes #2412
Fixes #2200
Fixes #632
This commit is contained in:
Erik Abair
2025-10-29 13:21:58 -07:00
committed by mborgerson
parent 95fdb7cd32
commit db8d27b9f4
1 changed files with 19 additions and 15 deletions
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hw/xbox/nv2a/pgraph/glsl/vsh.c
+19 -15
View File
@@ -223,6 +223,9 @@ MString *pgraph_glsl_gen_vsh(const VshState *state, GenVshGlslOptions opts)
"vec4 NaNToOne(vec4 src) {\n"
" return mix(src, vec4(1.0), isnan(src));\n"
"}\n"
"vec4 NaNToValue(vec4 src, float replacement) {\n"
" return mix(src, vec4(replacement), isnan(src));\n"
"}\n"
"\n"
// Xbox NV2A rasterizer appears to have 4 bit precision fixed-point
// fractional part and to convert floating-point coordinates by
@@ -321,6 +324,9 @@ MString *pgraph_glsl_gen_vsh(const VshState *state, GenVshGlslOptions opts)
/* FIXME: Do this per pixel? */
float infinite_fogdistance_result = 0.0f;
float nan_fogfactor_result = 0.0f;
switch (state->fog_mode) {
case FOG_MODE_LINEAR:
case FOG_MODE_LINEAR_ABS:
@@ -329,29 +335,21 @@ MString *pgraph_glsl_gen_vsh(const VshState *state, GenVshGlslOptions opts)
* fogParam.y = -1 / (end - start)
* fogParam.x = 1 - end * fogParam.y;
*/
mstring_append(body,
" if (isinf(fogDistance)) {\n"
" fogDistance = 0.0;\n"
" }\n"
);
infinite_fogdistance_result = 1.0f;
nan_fogfactor_result = 1.0f;
mstring_append(body, " float fogFactor = fogParam.x + fogDistance * fogParam.y;\n");
mstring_append(body, " fogFactor -= 1.0;\n");
break;
case FOG_MODE_EXP:
mstring_append(body,
" if (isinf(fogDistance)) {\n"
" fogDistance = 0.0;\n"
" }\n"
);
/* fallthru */
infinite_fogdistance_result = 1.0f;
nan_fogfactor_result = 1.0f;
/* fallthrough */
case FOG_MODE_EXP_ABS:
/* f = 1 / (e^(d * density))
* fogParam.y = -density / (2 * ln(256))
* fogParam.x = 1.5
*/
mstring_append(body, " float fogFactor = fogParam.x + exp2(fogDistance * fogParam.y * 16.0);\n");
mstring_append(body, " fogFactor -= 1.5;\n");
break;
@@ -384,8 +382,14 @@ MString *pgraph_glsl_gen_vsh(const VshState *state, GenVshGlslOptions opts)
* interpolation. It is then clamped to [0,1] in the pixel shader.
*/
// clang-format off
mstring_append(body,
" oFog = clamp(NaNToOne(vec4(fogFactor)), -FLOAT_MAX, FLOAT_MAX);\n");
mstring_append_fmt(
body,
" if (isinf(fogDistance)) {\n"
" oFog = vec4(%f);\n"
" } else {\n"
" oFog = clamp(NaNToValue(vec4(fogFactor), %f), -FLOAT_MAX, FLOAT_MAX);\n"
" }\n",
infinite_fogdistance_result, nan_fogfactor_result);
// clang-format on
}