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Optimize SkyMaterials by removing uses of acos and simplifying logic

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The results looks almost the same and run much faster.
This commit is contained in:
clayjohn
2025-01-23 20:03:19 -08:00
parent 09ea7bc6a3
commit 6fede0b951
4 changed files with 159 additions and 73 deletions
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28
drivers/gles3/shaders/sky.glsl
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@@ -151,6 +151,32 @@ vec4 fog_process(vec3 view, vec3 sky_color) {
}
#endif // !DISABLE_FOG
// Eberly approximations from https://seblagarde.wordpress.com/2014/12/01/inverse-trigonometric-functions-gpu-optimization-for-amd-gcn-architecture/.
// input [-1, 1] and output [0, PI]
float acos_approx(float p_x) {
float x = abs(p_x);
float res = -0.156583f * x + (M_PI / 2.0);
res *= sqrt(1.0f - x);
return (p_x >= 0) ? res : M_PI - res;
}
// Based on https://math.stackexchange.com/questions/1098487/atan2-faster-approximation
// but using the Eberly coefficients from https://seblagarde.wordpress.com/2014/12/01/inverse-trigonometric-functions-gpu-optimization-for-amd-gcn-architecture/.
float atan2_approx(float y, float x) {
float a = min(abs(x), abs(y)) / max(abs(x), abs(y));
float s = a * a;
float poly = 0.0872929f;
poly = -0.301895f + poly * s;
poly = 1.0f + poly * s;
poly = poly * a;
float r = abs(y) > abs(x) ? (M_PI / 2.0) - poly : poly;
r = x < 0.0 ? M_PI - r : r;
r = y < 0.0 ? -r : r;
return r;
}
void main() {
vec3 cube_normal;
#ifdef USE_MULTIVIEW
@@ -171,7 +197,7 @@ void main() {
vec2 uv = gl_FragCoord.xy; // uv_interp * 0.5 + 0.5;
vec2 panorama_coords = vec2(atan(cube_normal.x, -cube_normal.z), acos(cube_normal.y));
vec2 panorama_coords = vec2(atan2_approx(cube_normal.x, -cube_normal.z), acos_approx(cube_normal.y));
if (panorama_coords.x < 0.0) {
panorama_coords.x += M_PI * 2.0;