OK, so the projection matrix defines what 3D area that your game will draw from. What you’re trying to do is set it so the render target quad will be drawn over the whole screen. Using an identity matrix for the projection will draw everything in a cube-shaped area from (-1, -1, -1) to (1, 1, 1), so if that’s what you’re using, your flat render quad needs to cover the area from (-1, -1) to (1, 1). You can zoom way in on your main collection to see if that is the case. Possibly you just moved it by a pixel, or you may be using a model that goes from (0, 0) to (1, 1)?
If you want to use a different matrix, the vmath.matrix4_orthographic() function makes it simple, you just give it one coordinate for each side of the cube. So you can use whatever position and size of quad model you want to draw your render targets on, just set the projection matrix so it’s covers the same area.
You can also actually use a sprite, you don’t need a quad model. But the sprite needs to be in its own atlas and should fill the atlas completely (a power of 2 size), so the UVs aren’t weird.
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