Resectogram aspect ratio size

[RafaelPalomar]

We should find out what are reasonable options to modify the size and aspect ratio of the resectogram. Ideas:

• Double rendering pass (1st render to texture, 2nd transform the texture)
• Viewport manipulation

@RuoyanMeng, @olevs, @gatangen, @dalbenzioG

[RuoyanMeng]

Here I use the viewport only for the position of the 2D plane. I don't quite understand why we should use the viewport for adjusting the size of the Resectogram, cause anyway we still need to fake a 2D surface with whatever dimension to render. My solution now is to use the u/v ratio directly inside the shader so the size change will calculate in GPU.
I also tried lots of combination viewports to simulate your idea (x, y, width, height), in some cases, the renderwindow just couldn't show the 2D plane. From my point of view, manipulating the viewport may lead to many issues.

Also, I think the aspect ratio is only a temporal solution to give users a feeling that when they modify the resection surface, the 2D Resectogram would change accordingly. But in the end, we still need to find a way to do parametrically surface flattening inside GPU or in CPU if the algorithm is fast enough.