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.

4 files changed, 32 insertions, 1 deletions

diff --git a/source/blender/editors/space_node/drawnode.c b/source/blender/editors/space_node/drawnode.c
index d00d1e61b0d..7576e4791e1 100644
--- a/source/blender/editors/space_node/drawnode.c
+++ b/source/blender/editors/space_node/drawnode.c
@@ -809,9 +809,13 @@ static void node_shader_buts_tex_environment(uiLayout *layout, bContext *C, Poin
 }
 
 static void node_shader_buts_tex_sky(uiLayout *layout, bContext *UNUSED(C), PointerRNA *ptr)
-{
+{	
+	uiItemR(layout, ptr, "sky_type", 0, "", ICON_NONE);
 	uiItemR(layout, ptr, "sun_direction", 0, "", ICON_NONE);
 	uiItemR(layout, ptr, "turbidity", 0, NULL, ICON_NONE);
+
+	if (RNA_enum_get(ptr, "sky_type") == SHD_SKY_NEW)
+		uiItemR(layout, ptr, "ground_albedo", 0, NULL, ICON_NONE);
 }
 
 static void node_shader_buts_tex_gradient(uiLayout *layout, bContext *UNUSED(C), PointerRNA *ptr)
diff --git a/source/blender/makesdna/DNA_node_types.h b/source/blender/makesdna/DNA_node_types.h
index 6984d0299e8..e7eb670572a 100644
--- a/source/blender/makesdna/DNA_node_types.h
+++ b/source/blender/makesdna/DNA_node_types.h
@@ -720,8 +720,10 @@ typedef struct NodeTexBase {
 
 typedef struct NodeTexSky {
 	NodeTexBase base;
+	int sky_model;
 	float sun_direction[3];
 	float turbidity;
+	float ground_albedo;
 } NodeTexSky;
 
 typedef struct NodeTexImage {
@@ -937,6 +939,10 @@ typedef struct NodeShaderNormalMap {
 #define SHD_WAVE_BANDS		0
 #define SHD_WAVE_RINGS		1
 
+/* sky texture */
+#define SHD_SKY_OLD		0
+#define SHD_SKY_NEW		1
+
 /* image/environment texture */
 #define SHD_COLORSPACE_NONE		0
 #define SHD_COLORSPACE_COLOR	1
diff --git a/source/blender/makesrna/intern/rna_nodetree.c b/source/blender/makesrna/intern/rna_nodetree.c
index 6645e4f6de0..819d2613f29 100644
--- a/source/blender/makesrna/intern/rna_nodetree.c
+++ b/source/blender/makesrna/intern/rna_nodetree.c
@@ -3188,10 +3188,22 @@ static void def_sh_tex(StructRNA *srna)
 
 static void def_sh_tex_sky(StructRNA *srna)
 {
+	static EnumPropertyItem prop_sky_type[] = {
+		{SHD_SKY_OLD, "PREETHAM", 0, "Preetham", ""},
+		{SHD_SKY_NEW, "HOSEK_WILKIE", 0, "Hosek / Wilkie", ""},
+		{0, NULL, 0, NULL, NULL}
+	};
+	
 	PropertyRNA *prop;
 	
 	RNA_def_struct_sdna_from(srna, "NodeTexSky", "storage");
 	def_sh_tex(srna);
+
+	prop = RNA_def_property(srna, "sky_type", PROP_ENUM, PROP_NONE);
+	RNA_def_property_enum_sdna(prop, NULL, "sky_model");
+	RNA_def_property_enum_items(prop, prop_sky_type);
+	RNA_def_property_ui_text(prop, "Sky Type", "");
+	RNA_def_property_update(prop, 0, "rna_Node_update");
 	
 	prop = RNA_def_property(srna, "sun_direction", PROP_FLOAT, PROP_DIRECTION);
 	RNA_def_property_ui_text(prop, "Sun Direction", "Direction from where the sun is shining");
@@ -3199,8 +3211,14 @@ static void def_sh_tex_sky(StructRNA *srna)
 	
 	prop = RNA_def_property(srna, "turbidity", PROP_FLOAT, PROP_NONE);
 	RNA_def_property_range(prop, 1.0f, 30.0f);
+	RNA_def_property_ui_range(prop, 1.0f, 10.0f, 10, 3);
 	RNA_def_property_ui_text(prop, "Turbidity", "Atmospheric turbidity");
 	RNA_def_property_update(prop, NC_NODE | NA_EDITED, "rna_Node_update");
+	
+	prop = RNA_def_property(srna, "ground_albedo", PROP_FLOAT, PROP_NONE);
+	RNA_def_property_range(prop, 0.0f, 1.0f);
+	RNA_def_property_ui_text(prop, "Ground Albedo", "Ground color that is subtly reflected in the sky");
+	RNA_def_property_update(prop, NC_NODE | NA_EDITED, "rna_Node_update");
 }
 
 static void def_sh_tex_environment(StructRNA *srna)
diff --git a/source/blender/nodes/shader/nodes/node_shader_tex_sky.c b/source/blender/nodes/shader/nodes/node_shader_tex_sky.c
index f9cd4b72912..c80b5282de3 100644
--- a/source/blender/nodes/shader/nodes/node_shader_tex_sky.c
+++ b/source/blender/nodes/shader/nodes/node_shader_tex_sky.c
@@ -48,6 +48,8 @@ static void node_shader_init_tex_sky(bNodeTree *UNUSED(ntree), bNode *node)
 	tex->sun_direction[1] = 0.0f;
 	tex->sun_direction[2] = 1.0f;
 	tex->turbidity = 2.2f;
+	tex->ground_albedo = 0.3f;
+	tex->sky_model = SHD_SKY_NEW;
 
 	node->storage = tex;
 }
@@ -70,6 +72,7 @@ void register_node_type_sh_tex_sky(void)
 	sh_node_type_base(&ntype, SH_NODE_TEX_SKY, "Sky Texture", NODE_CLASS_TEXTURE, 0);
 	node_type_compatibility(&ntype, NODE_NEW_SHADING);
 	node_type_socket_templates(&ntype, sh_node_tex_sky_in, sh_node_tex_sky_out);
+	node_type_size_preset(&ntype, NODE_SIZE_MIDDLE);
 	node_type_init(&ntype, node_shader_init_tex_sky);
 	node_type_storage(&ntype, "NodeTexSky", node_free_standard_storage, node_copy_standard_storage);
 	node_type_gpu(&ntype, node_shader_gpu_tex_sky);