You can pass 0.5 as the 3rd parameter of the pass post process to use a texture dimension that is half the screen.
That’s essentially what you do when you set a with which is half the screen size, but it also applies to the height.
Also, I removed your render loop, the Playground is already setting its own.
Maybe this reference can help you if you want to draw antialiasing lines that are always at least one pixel large: