Sample as Lamp option for world shaders, to enable multiple importance sampling.

By default lighting from the world is computed solely with indirect light
sampling. However for more complex environment maps this can be too noisy, as
sampling the BSDF may not easily find the highlights in the environment map
image. By enabling this option, the world background will be sampled as a lamp,
with lighter parts automatically given more samples.

Map Resolution specifies the size of the importance map (res x res). Before
rendering starts, an importance map is generated by "baking" a grayscale image
from the world shader. This will then be used to determine which parts of the
background are light and so should receive more samples than darker parts.
Higher resolutions will result in more accurate sampling but take more setup
time and memory.

Patch by Mike Farnsworth, thanks!

1 files changed, 28 insertions, 6 deletions

diff --git a/intern/cycles/kernel/kernel_montecarlo.h b/intern/cycles/kernel/kernel_montecarlo.h
index df291b66b23..9776baf65e4 100644
--- a/intern/cycles/kernel/kernel_montecarlo.h
+++ b/intern/cycles/kernel/kernel_montecarlo.h
@@ -104,13 +104,13 @@ __device_inline void sample_uniform_hemisphere(const float3 N,
 
 __device float3 sample_uniform_sphere(float u1, float u2)
 {
-    float z = 1.0f - 2.0f*u1;
-    float r = sqrtf(fmaxf(0.0f, 1.0f - z*z));
-    float phi = 2.0f*M_PI_F*u2;
-    float x = r*cosf(phi);
-    float y = r*sinf(phi);
+	float z = 1.0f - 2.0f*u1;
+	float r = sqrtf(fmaxf(0.0f, 1.0f - z*z));
+	float phi = 2.0f*M_PI_F*u2;
+	float x = r*cosf(phi);
+	float y = r*sinf(phi);
 
-    return make_float3(x, y, z);
+	return make_float3(x, y, z);
 }
 
 __device float power_heuristic(float a, float b)
@@ -203,6 +203,28 @@ __device float3 spherical_to_direction(float theta, float phi)
 		cosf(theta));
 }
 
+/* Equirectangular */
+
+__device float2 direction_to_equirectangular(float3 dir)
+{
+	float u = (atan2f(dir.y, dir.x) + M_PI_F)/(2.0f*M_PI_F);
+	float v = atan2f(dir.z, hypotf(dir.x, dir.y))/M_PI_F + 0.5f;
+
+	return make_float2(u, v);
+}
+
+__device float3 equirectangular_to_direction(float u, float v)
+{
+	/* XXX check correctness? */
+	float theta = M_PI_F*v;
+	float phi = 2.0f*M_PI_F*u;
+
+	return make_float3(
+		sin(theta)*cos(phi),
+		sin(theta)*sin(phi),
+		cos(theta));
+}
+
 CCL_NAMESPACE_END
 
 #endif /* __KERNEL_MONTECARLO_CL__ */