WGL_ATI_pixel_format_float
http://oss.sgi.com/projects/ogl-sample/registry/ATI/pixel_format_float.txt
	WGL_TYPE_RGBA_FLOAT_ATI 0x21A0
	GL_RGBA_FLOAT_MODE_ATI 0x8820
	GL_COLOR_CLEAR_UNCLAMPED_VALUE_ATI 0x8835