Question How to draw input texture on top of the destination texture

Hello,
I am still learning to write shaders and currently, I am trying to create a composition shader of sorts.
I have a main texture which is e.g. 800x640 and I want to draw multiple various size images on top of that main texture.

So for example, I have this 800x640 texture and I want to draw two 95x150 size zombies on that texture at a certain position and in the correct size.



I use Graphics.Blit(), where I specify the source, destination textures, and material. I also send x and y source position coordinates and source size values. X and Y coordinates represent a position within the output texture so for example, x 400 and y 320 would be the middle of the output texture.

Also, some images might be outside the output texture or can be way larger than the output texture itself.

How can I achieve such a result?