World textures displaying for viewport in BI.

This patch supports "Image or Movie" and "Environment map" types of world texture for the viewport.
It supports:

  - "View", "AngMap" and "Equirectangular" types of mapping.

  - Different types of texture blending (according to BI world render).

  - Same color blending as when it lacked textures (but render via glsl).

{F207734}
{F207735}

Example: {F275180}
Original author: @valentin_b4w

Regards,
Alexander (Blend4Web Team).

Reviewers: sergey, valentin_b4w, brecht, merwin

Reviewed By: merwin

Subscribers: campbellbarton, merwin, blueprintrandom, youle, a.romanov, yurikovelenov, AlexKowel, Evgeny_Rodygin

Projects: #rendering, #opengl_gfx, #bf_blender:_next

Differential Revision: https://developer.blender.org/D1414

source/blender/gpu/GPU_material.h

@@ -78,6 +78,7 @@ typedef enum GPUType {
 
 	GPU_TEX2D = 1002,
 	GPU_SHADOW2D = 1003,
+	GPU_TEXCUBE = 1004,
 	GPU_ATTRIB = 3001
 } GPUType;
 
@@ -179,6 +180,7 @@ typedef enum GPUDynamicType {
 
 	GPU_DYNAMIC_HORIZON_COLOR        = 1  | GPU_DYNAMIC_GROUP_WORLD,
 	GPU_DYNAMIC_AMBIENT_COLOR        = 2  | GPU_DYNAMIC_GROUP_WORLD,
+	GPU_DYNAMIC_ZENITH_COLOR         = 3  | GPU_DYNAMIC_GROUP_WORLD,
 
 	GPU_DYNAMIC_MAT_DIFFRGB          = 1  | GPU_DYNAMIC_GROUP_MAT,
 	GPU_DYNAMIC_MAT_REF              = 2  | GPU_DYNAMIC_GROUP_MAT,
@@ -194,6 +196,7 @@ GPUNodeLink *GPU_attribute(CustomDataType type, const char *name);
 GPUNodeLink *GPU_uniform(float *num);
 GPUNodeLink *GPU_dynamic_uniform(float *num, GPUDynamicType dynamictype, void *data);
 GPUNodeLink *GPU_image(struct Image *ima, struct ImageUser *iuser, bool is_data);
+GPUNodeLink *GPU_cube_map(struct Image *ima, struct ImageUser *iuser, bool is_data);
 GPUNodeLink *GPU_image_preview(struct PreviewImage *prv);
 GPUNodeLink *GPU_texture(int size, float *pixels);
 GPUNodeLink *GPU_dynamic_texture(struct GPUTexture *tex, GPUDynamicType dynamictype, void *data);