Add sky light, physical atmosphere, auto exposure and bloom to the GL 4.6 renderer

gl/cubemap.h

@@ -13,6 +13,9 @@ namespace gl
         ~cubemap();
 
         void alloc(GLint format, int width, int height, GLenum components, GLenum type) const;
+        // immutable storage of square faces with the given number of mipmap levels, filtered between the levels.
+        // the levels are meant to be written by compute shaders (glBindImageTexture), so format has to be an image format
+        void alloc_levels(GLenum format, int size, int levels) const;
         void bind(int unit) const;
         void generate_mipmaps() const;
     };