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Cleanup: simplify computation in Cycles area light sampling

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`diff` in numerator and denominator cancels out, except for the signs,
which we know beforehand since `x1 > x0`, `y1 > y0`

Pull Request: https://projects.blender.org/blender/blender/pulls/122740
This commit is contained in:
Weizhen Huang 2024-06-04 23:37:48 +02:00 • committed by Weizhen Huang
parent c1a9ccdf0b
commit 2ddc936cbb
2 changed files with 7 additions and 3 deletions
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5
intern/cycles/kernel/light/area.h
View file

@ -39,9 +39,8 @@ ccl_device_inline float area_light_rect_sample(float3 P,
float x0 = xc - 0.5f * len_u, x1 = xc + 0.5f * len_u;
float y0 = yc - 0.5f * len_v, y1 = yc + 0.5f * len_v;
/* Compute predefined constants. */
float4 diff = make_float4(x0, y1, x1, y0) - make_float4(x1, y0, x0, y1);
float4 nz = make_float4(y0, x1, y1, x0) * diff;
nz = nz / sqrt(z0 * z0 * diff * diff + nz * nz);
float4 nz = make_float4(-y0, x1, y1, -x0);
nz /= sqrt(nz * nz + z0 * z0);
/* The original paper uses `acos()` to compute the internal angles here, and then computes the
* solid angle as their sum minus 2*pi. However, for very small rectangles, this results in
* excessive cancellation error since the sum will be almost 2*pi as well.

5
intern/cycles/util/math_float4.h
View file

@ -132,6 +132,11 @@ ccl_device_inline float4 operator*=(float4 &a, float f)
return a = a * f;
}
ccl_device_inline float4 operator/=(float4 &a, const float4 b)
{
return a = a / b;
}
ccl_device_inline float4 operator/=(float4 &a, float f)
{
return a = a / f;