Cycles: support for environment texture "Mirror Ball" projection mode, next to

existing "Equirectangular". This projection is useful to create light probes
from a chrome ball placed in a real scene. It expects as input a photograph of
the chrome ball, cropped so the ball just fits inside the image boundaries.

Example setup with panorama camera and mixing two (poor quality) photographs
from different viewpoints to avoid stretching and hide the photographer:
http://www.pasteall.org/pic/28036

1 files changed, 32 insertions, 0 deletions

diff --git a/intern/cycles/kernel/kernel_montecarlo.h b/intern/cycles/kernel/kernel_montecarlo.h
index 66bd0ee9998..68f007cfd97 100644
--- a/intern/cycles/kernel/kernel_montecarlo.h
+++ b/intern/cycles/kernel/kernel_montecarlo.h
@@ -224,6 +224,38 @@ __device float3 equirectangular_to_direction(float u, float v)
 		cos(theta));
 }
 
+/* Mirror Ball <-> Cartesion direction */
+
+__device float3 mirrorball_to_direction(float u, float v)
+{
+	/* point on sphere */
+	float3 dir;
+
+	dir.x = 2.0f*u - 1.0f;
+	dir.z = 2.0f*v - 1.0f;
+	dir.y = -sqrt(max(1.0f - dir.x*dir.x - dir.z*dir.z, 0.0f));
+
+	/* reflection */
+	float3 I = make_float3(0.0f, -1.0f, 0.0f);
+
+	return 2.0f*dot(dir, I)*dir - I;
+}
+
+__device float2 direction_to_mirrorball(float3 dir)
+{
+	/* inverse of mirrorball_to_direction */
+	dir.y -= 1.0f;
+
+	float div = 2.0f*sqrt(max(-0.5f*dir.y, 0.0f));
+	if(div > 0.0f)
+		dir /= div;
+
+	float u = 0.5f*(dir.x + 1.0f);
+	float v = 0.5f*(dir.z + 1.0f);
+
+	return make_float2(u, v);
+}
+
 CCL_NAMESPACE_END
 
 #endif /* __KERNEL_MONTECARLO_CL__ */