Converts main level of the GL texture to TImageData strucrue.

function CreateImageFromGLTexture(const Texture: GLuint; 
                                  var Image: TImageData; 
                                  OverrideFormat: TImageFormat = ifUnknown): Boolean;

ImagingOpenGL (at line 150)

OverrideFormat can be used to convert output image to the specified format rather than use the format taken from GL texture, ifUnknown means no conversion.