Cycles / Sky Texture:

* Added a new sky model by Hosek and Wilkie: "An Analytic Model for Full Spectral Sky-Dome Radiance" http://cgg.mff.cuni.cz/projects/SkylightModelling/ 

Example render:
http://archive.dingto.org/2013/blender/code/new_sky_model.png
Documentation:
http://wiki.blender.org/index.php/Doc:2.6/Manual/Render/Cycles/Nodes/Textures#Sky_Texture

Details:
* User can choose between the older Preetham and the new Hosek / Wilkie model via a dropdown. For older files, backwards compatibility is preserved. When we add a new Sky texture, it defaults to the new model though. 
* For the new model, you can specify the ground albedo (see documentation for details). 
* Turbidity now has a UI soft range between 1 and 10, higher values (up to 30) are still possible, but can result in weird colors or black. 
* Removed the limitation of 1 sky texture per SVM stack. (Patch by Lukas Tönne, thanks!)

Thanks to Brecht for code review and some help! 

This is part of my GSoC 2013 project, SVN merge of r59214, r59220, r59251 and r59601.

1 files changed, 125 insertions, 11 deletions

diff --git a/intern/cycles/kernel/svm/svm_sky.h b/intern/cycles/kernel/svm/svm_sky.h
index c4e0ca3e242..cb6e5def4bd 100644
--- a/intern/cycles/kernel/svm/svm_sky.h
+++ b/intern/cycles/kernel/svm/svm_sky.h
@@ -16,10 +16,7 @@
 
 CCL_NAMESPACE_BEGIN
 
-/*
- * "A Practical Analytic Model for Daylight"
- * A. J. Preetham, Peter Shirley, Brian Smits
- */
+/* Sky texture */
 
 __device float sky_angle_between(float thetav, float phiv, float theta, float phi)
 {
@@ -27,6 +24,10 @@ __device float sky_angle_between(float thetav, float phiv, float theta, float ph
 	return safe_acosf(cospsi);
 }
 
+/*
+ * "A Practical Analytic Model for Daylight"
+ * A. J. Preetham, Peter Shirley, Brian Smits
+ */
 __device float sky_perez_function(__constant float *lam, float theta, float gamma)
 {
 	float ctheta = cosf(theta);
@@ -35,7 +36,10 @@ __device float sky_perez_function(__constant float *lam, float theta, float gamm
 	return (1.0f + lam[0]*expf(lam[1]/ctheta)) * (1.0f + lam[2]*expf(lam[3]*gamma)  + lam[4]*cgamma*cgamma);
 }
 
-__device float3 sky_radiance(KernelGlobals *kg, float3 dir)
+__device float3 sky_radiance_old(KernelGlobals *kg, float3 dir,
+                                 float sunphi, float suntheta,
+                                 float radiance_x, float radiance_y, float radiance_z,
+                                 float *config_x, float *config_y, float *config_z)
 {
 	/* convert vector to spherical coordinates */
 	float2 spherical = direction_to_spherical(dir);
@@ -43,25 +47,135 @@ __device float3 sky_radiance(KernelGlobals *kg, float3 dir)
 	float phi = spherical.y;
 
 	/* angle between sun direction and dir */
-	float gamma = sky_angle_between(theta, phi, kernel_data.sunsky.theta, kernel_data.sunsky.phi);
+	float gamma = sky_angle_between(theta, phi, suntheta, sunphi);
 
 	/* clamp theta to horizon */
 	theta = min(theta, M_PI_2_F - 0.001f);
 
 	/* compute xyY color space values */
-	float x = kernel_data.sunsky.zenith_x * sky_perez_function(kernel_data.sunsky.perez_x, theta, gamma);
-	float y = kernel_data.sunsky.zenith_y * sky_perez_function(kernel_data.sunsky.perez_y, theta, gamma);
-	float Y = kernel_data.sunsky.zenith_Y * sky_perez_function(kernel_data.sunsky.perez_Y, theta, gamma);
+	float x = radiance_y * sky_perez_function(config_y, theta, gamma);
+	float y = radiance_z * sky_perez_function(config_z, theta, gamma);
+	float Y = radiance_x * sky_perez_function(config_x, theta, gamma);
 
 	/* convert to RGB */
 	float3 xyz = xyY_to_xyz(x, y, Y);
 	return xyz_to_rgb(xyz.x, xyz.y, xyz.z);
 }
 
-__device void svm_node_tex_sky(KernelGlobals *kg, ShaderData *sd, float *stack, uint dir_offset, uint out_offset)
+/*
+ * "An Analytic Model for Full Spectral Sky-Dome Radiance"
+ * Lukas Hosek, Alexander Wilkie
+ */
+__device float sky_radiance_internal(__constant float *configuration, float theta, float gamma)
+{
+	float ctheta = cosf(theta);
+	float cgamma = cosf(gamma);
+
+	float expM = expf(configuration[4] * gamma);
+	float rayM = cgamma * cgamma;
+	float mieM = (1.0f + rayM) / powf((1.0f + configuration[8]*configuration[8] - 2.0f*configuration[8]*cgamma), 1.5f);
+	float zenith = sqrt(ctheta);
+
+	return (1.0f + configuration[0] * expf(configuration[1] / (ctheta + 0.01f))) *
+		(configuration[2] + configuration[3] * expM + configuration[5] * rayM + configuration[6] * mieM + configuration[7] * zenith);
+}
+
+__device float3 sky_radiance_new(KernelGlobals *kg, float3 dir,
+                                 float sunphi, float suntheta,
+                                 float radiance_x, float radiance_y, float radiance_z,
+                                 float *config_x, float *config_y, float *config_z)
 {
+	/* convert vector to spherical coordinates */
+	float2 spherical = direction_to_spherical(dir);
+	float theta = spherical.x;
+	float phi = spherical.y;
+
+	/* angle between sun direction and dir */
+	float gamma = sky_angle_between(theta, phi, suntheta, sunphi);
+
+	/* clamp theta to horizon */
+	theta = min(theta, M_PI_2_F - 0.001f);
+
+	/* compute xyz color space values */
+	float x = sky_radiance_internal(config_x, theta, gamma) * radiance_x;
+	float y = sky_radiance_internal(config_y, theta, gamma) * radiance_y;
+	float z = sky_radiance_internal(config_z, theta, gamma) * radiance_z;
+
+	/* convert to RGB and adjust strength */
+	return xyz_to_rgb(x, y, z) * (M_2PI_F/683);
+}
+
+__device void svm_node_tex_sky(KernelGlobals *kg, ShaderData *sd, float *stack, uint4 node, int *offset)
+{
+	/* Define variables */
+	float sunphi, suntheta, radiance_x, radiance_y, radiance_z;
+	float config_x[9], config_y[9], config_z[9];
+	
+	/* Load data */
+	uint dir_offset = node.y;
+	uint out_offset = node.z;
+	int sky_model = node.w;
+
+	float4 data = read_node_float(kg, offset);
+	sunphi = data.x;
+	suntheta = data.y;
+	radiance_x = data.z;
+	radiance_y = data.w;
+	
+	data = read_node_float(kg, offset);
+	radiance_z = data.x;
+	config_x[0] = data.y;
+	config_x[1] = data.z;
+	config_x[2] = data.w;
+	
+	data = read_node_float(kg, offset);
+	config_x[3] = data.x;
+	config_x[4] = data.y;
+	config_x[5] = data.z;
+	config_x[6] = data.w;
+	
+	data = read_node_float(kg, offset);
+	config_x[7] = data.x;
+	config_x[8] = data.y;
+	config_y[0] = data.z;
+	config_y[1] = data.w;
+	
+	data = read_node_float(kg, offset);
+	config_y[2] = data.x;
+	config_y[3] = data.y;
+	config_y[4] = data.z;
+	config_y[5] = data.w;
+	
+	data = read_node_float(kg, offset);
+	config_y[6] = data.x;
+	config_y[7] = data.y;
+	config_y[8] = data.z;
+	config_z[0] = data.w;
+	
+	data = read_node_float(kg, offset);
+	config_z[1] = data.x;
+	config_z[2] = data.y;
+	config_z[3] = data.z;
+	config_z[4] = data.w;
+	
+	data = read_node_float(kg, offset);
+	config_z[5] = data.x;
+	config_z[6] = data.y;
+	config_z[7] = data.z;
+	config_z[8] = data.w;
+	
 	float3 dir = stack_load_float3(stack, dir_offset);
-	float3 f = sky_radiance(kg, dir);
+	float3 f;
+
+	/* Compute Sky */
+	if(sky_model == 0)
+		f = sky_radiance_old(kg, dir, sunphi, suntheta,
+	                             radiance_x, radiance_y, radiance_z,
+	                             config_x, config_y, config_z);
+	else
+		f = sky_radiance_new(kg, dir, sunphi, suntheta,
+	                             radiance_x, radiance_y, radiance_z,
+	                             config_x, config_y, config_z);
 
 	stack_store_float3(stack, out_offset, f);
 }