problem with extrapolating parts of a texture

I have a plugin that returns me a Texture that contains two images one above the other like so:

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the top image is the right camera output of the Vive Pro and the bottom is the left camera.
I need to put these images side by side, with the left camera output on the left like so:

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Is there a way to do this that isn't CPU intensive?

Blitting won't suffice since there's no way of specifying which part of the rendertexture you want to blit into, right?
I've looked into shaders, but even if I manage to separate the images into two separate textures I can't figure out how to write the shader so that I can put those two textures side by side.

 

you could have single plane mesh (or 2 quads), with suitable UV mapping.
so that the top texture is drawn on left half and bottom texture to right side.

 

It's possible to make an inefficient shader to do everything you need, but mgear's solution is the best.

 

@mgear unfortunately I don't think I can do that! If I understood correctly, you're saying to create a mesh and tailor the UV mapping right? If so, that won't work because I'm supplying the texture to an OpenVR Overlay, which just takes a texture in input and uses it's own mesh internally I'm guessing.

 

Maybe I am misunderstanding, but why can't you just make a Texture2D and do a getpixel from the source and setpixel on the new texture you are making?

 

Because that is really slow. However, it's along the right idea.
https://docs.unity3d.com/ScriptReference/Graphics.CopyTexture.html
CopyTexture supports copying texture regions from one texture to another with offsets into the destination.

 

I completely missed that!
Unfortunately it's not working correctly.
This is the source texture:

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and this is the destination texture:

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this is simply using

Code (CSharp):

1. Graphics.CopyTexture(texture, 0, 0, combinedTexture, 0, 0);

while using

Code (CSharp):

1. Graphics.CopyTexture(texture, 0, 0, 0, 0, 1224, 920, combinedTexture, 0, 0, 0, 0);

gives me this:

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(the intent would be to take just the bottom image)

As you can see, the source texture is 0 bytes, because it's actually an external texture (created through Texture2D.CreateExternalTexture()), could that have to do with it?

EDIT: never mind, apparently texture.width/height is unreliable on externally created textures, you should be getting width & height from the plugin that is creating the external texture.

P:S: Also, is CopyTexture faster than Blit for simplying copying a texture to a rendertexture?

 

It should be much faster, or at least no slower.