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Cycles: Save a few instructions in area light sampling

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Just basic algebra - because all vectors have the same z coordinate, a lot of terms end up cancelling out.

Not exactly a massive improvement, but it's measurable with Branched PT and a high sample count on the lamp.

Reviewers: brecht, sergey

Reviewed By: brecht

Subscribers: swerner

Differential Revision: https://developer.blender.org/D3540
This commit is contained in:
Lukas Stockner
2018-07-27 23:30:20 +02:00
parent 84d47e3685
commit bcefb202a2
1 changed files with 9 additions and 16 deletions
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25
intern/cycles/kernel/kernel_light.h
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@@ -72,24 +72,17 @@ ccl_device_inline float area_light_sample(float3 P,
float y0 = dot(dir, y); float y0 = dot(dir, y);
float x1 = x0 + axisu_len; float x1 = x0 + axisu_len;
float y1 = y0 + axisv_len; float y1 = y0 + axisv_len;
/* Create vectors to four vertices. */
float3 v00 = make_float3(x0, y0, z0);
float3 v01 = make_float3(x0, y1, z0);
float3 v10 = make_float3(x1, y0, z0);
float3 v11 = make_float3(x1, y1, z0);
/* Compute normals to edges. */
float3 n0 = normalize(cross(v00, v10));
float3 n1 = normalize(cross(v10, v11));
float3 n2 = normalize(cross(v11, v01));
float3 n3 = normalize(cross(v01, v00));
/* Compute internal angles (gamma_i). */ /* Compute internal angles (gamma_i). */
float g0 = safe_acosf(-dot(n0, n1)); float4 diff = make_float4(x0, y1, x1, y0) - make_float4(x1, y0, x0, y1);
float g1 = safe_acosf(-dot(n1, n2)); float4 nz = make_float4(y0, x1, y1, x0) * diff;
float g2 = safe_acosf(-dot(n2, n3)); nz = nz / sqrt(sqr(z0 * diff) + sqr(nz));
float g3 = safe_acosf(-dot(n3, n0)); float g0 = safe_acosf(-nz.x * nz.y);
float g1 = safe_acosf(-nz.y * nz.z);
float g2 = safe_acosf(-nz.z * nz.w);
float g3 = safe_acosf(-nz.w * nz.x);
/* Compute predefined constants. */ /* Compute predefined constants. */
float b0 = n0.z; float b0 = nz.x;
float b1 = n2.z; float b1 = nz.z;
float b0sq = b0 * b0; float b0sq = b0 * b0;
float k = M_2PI_F - g2 - g3; float k = M_2PI_F - g2 - g3;
/* Compute solid angle from internal angles. */ /* Compute solid angle from internal angles. */