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/intern/gpu_extensions.c

@@ -73,6 +73,7 @@
 
 static struct GPUGlobal {
 	GLint maxtexsize;
+	GLint maxcubemapsize;
 	GLint maxtextures;
 	bool extdisabled;
 	int colordepth;
@@ -120,6 +121,11 @@ int GPU_max_color_texture_samples(void)
 	return GG.samples_color_texture_max;
 }
 
+int GPU_max_cube_map_size(void)
+{
+	return GG.maxcubemapsize;
+}
+
 void GPU_get_dfdy_factors(float fac[2])
 {
 	copy_v2_v2(fac, GG.dfdyfactors);
@@ -133,6 +139,7 @@ void gpu_extensions_init(void)
 	glGetIntegerv(GL_MAX_TEXTURE_IMAGE_UNITS, &GG.maxtextures);
 
 	glGetIntegerv(GL_MAX_TEXTURE_SIZE, &GG.maxtexsize);
+	glGetIntegerv(GL_MAX_CUBE_MAP_TEXTURE_SIZE, &GG.maxcubemapsize);
 
 	if (GLEW_EXT_texture_filter_anisotropic)
 		glGetFloatv(GL_MAX_TEXTURE_MAX_ANISOTROPY_EXT, &GG.max_anisotropy);