Using viewport with RenderTarget

Questions
1

I need to render a scene on a specific location inside a render target (for creating texture atlas).
So I memorize the current viewport then switch targets, render and put the old viewport back, like so:

const renderRTVP = (rend, scene, camera, outputRT, vp, clear = true) => {
	const bool = !clear && rend.autoClear;
	if (bool) rend.autoClear = false;
	const vp_old = new THREE.Vector4();
	rend.getCurrentViewport(vp_old);
	rend.setRenderTarget(outputRT);
	rend.setViewport(vp);
	rend.render(scene, camera);
	rend.setViewport(vp_old);
	rend.setRenderTarget(null);
	if(bool) rend.autoClear = true;
};

is this the right code?

it works under Windows 10 but doesn’t work on Android mobile and probably other OS.

This is what I see when I press both buttons:

rtvp
rtvp896×816 7.84 KB

  1. What’s the difference between getCurrentViewport and getViewport, I see different sizes on mobile?

  2. Does the order of calling setRenderTarget and setViewport matter?

2

Not sure if you’ve looked at code for portal example. It doesn’t seem to need to use viewport

3

The stereo example uses two view ports. Looks like the code for Stereo Effect doesn’t attempt to restore the viewport.

4

Thanks, but, unfortunately, it doesn’t help me much.
In the portal example, each portal uses its own texture that is rendered in full size, so there is no need to use a viewport inside it, in the second example the viewport is not restored because stereo effect is run on each frame and it resets scissors and viewport halves from scratch.

5

Ok, for the record, currentViewport is Viewport multiplied by window.devicePixelRatio which will break your code if you apply that to a render texture that is sized in “true” pixels as it will be out of bounds.