GL_AMD_framebuffer_sample_positions
http://www.opengl.org/registry/specs/AMD/framebuffer_sample_positions.txt
GL_AMD_framebuffer_sample_positions

	GL_SUBSAMPLE_DISTANCE_AMD 0x883F
	GL_PIXELS_PER_SAMPLE_PATTERN_X_AMD 0x91AE
	GL_PIXELS_PER_SAMPLE_PATTERN_Y_AMD 0x91AF
	GL_ALL_PIXELS_AMD 0xFFFFFFFF
	void glFramebufferSamplePositionsfvAMD (GLenum target, GLuint numsamples, GLuint pixelindex, const GLfloat* values)
	void glGetFramebufferParameterfvAMD (GLenum target, GLenum pname, GLuint numsamples, GLuint pixelindex, GLsizei size, GLfloat* values)
	void glGetNamedFramebufferParameterfvAMD (GLuint framebuffer, GLenum pname, GLuint numsamples, GLuint pixelindex, GLsizei size, GLfloat* values)
	void glNamedFramebufferSamplePositionsfvAMD (GLuint framebuffer, GLuint numsamples, GLuint pixelindex, const GLfloat* values)
