Weird behavior with Flame Shaders compared to pure flutter shader

### What happened?

Trying to use a shader that works in pure Flutter, it doesn't in Flame. My picture gets scaled down and asymmetrically deformed. This might be simply something I don't understand with how to pass data to the shader in Flame, or a bug, I'm unsure.

### What do you expect?

I'm trying to reproduce the same behavior in pure flutter and in Flame, On the right
the expected result and on the left the one I'm getting with Flame.

### How can we reproduce this?

I made a public repo to work on the issue you can take a look at
https://github.com/stilnat/shader-flame-test

### What steps should take to fix this?

I don't know at all