Render TOP post 'crop' projection matrix?

General TouchDesigner Discussion
1

I am working with the ‘crop’ parameters on the render TOP as a way to center certain objects in a render and now want to re-project the image back into some geometry however I am struggling to re-construct whatever the crop parameters are doing to the projection matrix in order to do the centering in the first place. It seems if I could retrieve or otherwise figure out how to apply the same crop settings to a custom projection matrix I would be set. I am curious if anyone has anything to suggest- thanks!

2

The projection crop is a basic re-range operation applied after the projection: (this is C++ code)

// Scale to 0, 1 range
proj->scale(0.5f, 0.5f, 1.0f);
proj->translate(0.5f, 0.5f, 0.0f);

// now rescale to the crop
proj->translate(-cropX0, -cropY0, 0.0f);
proj->scale(1.0f / (cropX1 - cropX0), 1.0f / (cropY1- cropY0), 1.0f);

// Rescale to -1, 1
proj->translate(-0.5f, -0.5f, 0.0f);
proj->scale(2.0f, 2.0f, 1.0f);
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3

Awesome, thanks. Bear with me I’m learning… Would I want to apply this math in the vertex or pixel shader? I am currently using the attached GLSL MAT for texture projection and fiddling with it to modify for this purpose.

alphaProj.tox (1.9 KB)

4

I’m able to mess with position by manipulating worldSpacePos however that’s world space and I think I want to move the projection texture around in screen space? In order to rescale / translate it to counteract the scaling and cropping of the original render.

5

TDWorldToProj() will apply the projections and leave the position in clip space. If you then want to undo the above scales/translations, you’d apply them to that after, in the vertex shader.

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6

Thank you so much for the info- I ended up getting the camera projection matrix and using this math with the matrix class to do the ‘de-crop’. Works great, will try to do it direct in vertex shader next. This helped shore up a lot my understanding of projection matrices- thank you again.