Revert "Cycles: Remove the Preetham Sky model."

This reverts commit d91316dc672dc1ee69fbd24d2f00124a24b75c6b.

2 files changed, 58 insertions, 7 deletions

diff --git a/intern/cycles/kernel/svm/svm_sky.h b/intern/cycles/kernel/svm/svm_sky.h
index 28599f550b6..854e85fd326 100644
--- a/intern/cycles/kernel/svm/svm_sky.h
+++ b/intern/cycles/kernel/svm/svm_sky.h
@@ -25,6 +25,44 @@ ccl_device float sky_angle_between(float thetav, float phiv, float theta, float
 }
 
 /*
+ * "A Practical Analytic Model for Daylight"
+ * A. J. Preetham, Peter Shirley, Brian Smits
+ */
+ccl_device float sky_perez_function(float *lam, float theta, float gamma)
+{
+	float ctheta = cosf(theta);
+	float cgamma = cosf(gamma);
+
+	return (1.0f + lam[0]*expf(lam[1]/ctheta)) * (1.0f + lam[2]*expf(lam[3]*gamma)  + lam[4]*cgamma*cgamma);
+}
+
+ccl_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);
+	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 xyY color space values */
+	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);
+}
+
+/*
  * "An Analytic Model for Full Spectral Sky-Dome Radiance"
  * Lukas Hosek, Alexander Wilkie
  */
@@ -42,10 +80,10 @@ ccl_device float sky_radiance_internal(float *configuration, float theta, float
 		(configuration[2] + configuration[3] * expM + configuration[5] * rayM + configuration[6] * mieM + configuration[7] * zenith);
 }
 
-ccl_device float3 sky_radiance(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)
+ccl_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);
@@ -76,6 +114,7 @@ ccl_device void svm_node_tex_sky(KernelGlobals *kg, ShaderData *sd, float *stack
 	/* 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;
@@ -129,9 +168,16 @@ ccl_device void svm_node_tex_sky(KernelGlobals *kg, ShaderData *sd, float *stack
 	float3 f;
 
 	/* Compute Sky */
-	f = sky_radiance(kg, dir, sunphi, suntheta,
-	                 radiance_x, radiance_y, radiance_z,
-	                 config_x, config_y, config_z);
+	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);
 }
diff --git a/intern/cycles/kernel/svm/svm_types.h b/intern/cycles/kernel/svm/svm_types.h
index f9d741f06c8..21b0cb15a4f 100644
--- a/intern/cycles/kernel/svm/svm_types.h
+++ b/intern/cycles/kernel/svm/svm_types.h
@@ -299,6 +299,11 @@ typedef enum NodeWaveProfiles {
 	NODE_WAVE_PROFILE_SAW,
 } NodeWaveProfile;
 
+typedef enum NodeSkyType {
+	NODE_SKY_OLD,
+	NODE_SKY_NEW
+} NodeSkyType;
+
 typedef enum NodeGradientType {
 	NODE_BLEND_LINEAR,
 	NODE_BLEND_QUADRATIC,