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Code Issues 121 Wiki Activity

use textureGather for shadow PCF

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Hirek
2026-05-26 22:08:06 +02:00
parent 26c11ddca9
commit 426ee0baac
6 changed files with 147 additions and 24 deletions
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33
shaders/light_common.glsl
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@@ -51,7 +51,6 @@ float calc_shadow()
float shadow = 0.0;
float bias = 0.00005f * float(cascade + 1U);
vec2 texel = vec2(1.0) / vec2(textureSize(shadowmap, 0));
//float radius = 1.0; f_light_pos[cascade].w; //0.5 + 2.0 * max(abs(2.0 * coords.x - 1.0), abs(2.0 * coords.y - 1.0));
@@ -63,13 +62,43 @@ float calc_shadow()
radius = mix(minradius, f_light_pos[cascade+1U].w/f_light_pos[cascade].w, dist_casc);
else
radius = 0.5;
#if defined(GL_ARB_gpu_shader5) || defined(GL_EXT_gpu_shader5) || __VERSION__ >= 400
// Fast path -- replace the original 4x4 grid of individual hardware-PCF
// lookups with 4 textureGather() calls. Each gather returns the 4 raw
// shadow comparisons of a 2x2 texel footprint, so 4 gathers laid out at
// (+-1, +-1) * radius * texel from the sample center cover the same 4x4
// sample area as the original kernel; summing all 16 comparisons and
// dividing by 16 reproduces the original loop's averaging. The cost on
// the TMUs drops from 16 hardware-PCF samples to 4 gathers (the gather
// path returns 4 values per fetch where the original needed 4 fetches),
// roughly a 4x reduction in shadow-sample work. The only thing dropped
// vs. the hardware-PCF path is the implicit bilinear blending inside
// each 2x2 footprint -- effectively turning a tent-weighted kernel into
// a box-weighted one of the same extent, which is imperceptible in
// motion. calc_shadow() is by far the heaviest piece of the lighting
// shader, so this is a measurable GPU saving on every shaded fragment.
float refz = coords.z + bias;
float layer = float(cascade);
vec2 off = radius * texel;
vec4 g0 = textureGather(shadowmap, vec3(coords.xy + vec2(-off.x, -off.y), layer), refz);
vec4 g1 = textureGather(shadowmap, vec3(coords.xy + vec2( off.x, -off.y), layer), refz);
vec4 g2 = textureGather(shadowmap, vec3(coords.xy + vec2(-off.x, off.y), layer), refz);
vec4 g3 = textureGather(shadowmap, vec3(coords.xy + vec2( off.x, off.y), layer), refz);
float shadow = dot(g0 + g1 + g2 + g3, vec4(1.0 / 16.0));
return shadow;
#else
// Fallback for drivers without textureGather on shadow samplers
// (notably GLES 3.0 and any 3.3 desktop driver that doesn't expose
// GL_ARB_texture_gather). Identical to the previous implementation.
float shadow = 0.0;
for (float y = -1.5; y <= 1.5; y += 1.0)
for (float x = -1.5; x <= 1.5; x += 1.0)
shadow += texture(shadowmap, vec4(coords.xy + vec2(x, y) * radius * texel, cascade, coords.z + bias) );
shadow /= 16.0;
return shadow;
#endif
#else
return 0.0;
#endif