[vtkusers] ImageMapper and ImageActor, OpenGL and Win32

[John Biddiscombe]

Image actor only handles images as OpenGL textures, (hence pretty poor 
resolution and only power of 2). Image mapper can handle Win32 GDI bitmap 
and render high quality images.

Can one replace the code in ImageActor with a GDI alternative and thereby 
get an image actor with decent quality output. (ie vtkWin32ImageActor 
instead of vtkOpenGLImageActor)

This boils down to a question off whether a GDI bitblt can be inserted 
between the OpenGL calls going on in the normal render sequence.

(what I want to do is modify vtkXYPlotActor to display 2D plots of data, 
but it handles all its primitives using OpenGL and displaying an image 
using win32 between other OpenGLprimitives may be troublesome)

Is it OK to do this?

JB