GL_OES_blend_func_separate
https://www.khronos.org/registry/OpenGL/extensions/OES/OES_blend_func_separate.txt
GL_OES_blend_func_separate

	GL_BLEND_DST_RGB_OES 0x80C8
	GL_BLEND_SRC_RGB_OES 0x80C9
	GL_BLEND_DST_ALPHA_OES 0x80CA
	GL_BLEND_SRC_ALPHA_OES 0x80CB
	void glBlendFuncSeparateOES (GLenum sfactorRGB, GLenum dfactorRGB, GLenum sfactorAlpha, GLenum dfactorAlpha)