GL.Viewport
static function Viewport(pixelRect: Rect): void;
static void Viewport(Rect pixelRect);
static def Viewport(pixelRect as Rect) as void
Description

Set the rendering viewport.

All rendering is constrained to be inside the passed pixelRect.
If the Viewport is modified, all the rendered content inside of it gets stretched.
	// Draw a red Quad that covers all the view port, and the when space is pressed
	// the viewport gets expanded to the whole screen and stretch the contents inside
	var mat : Material;
	private var stretch : boolean = false;

function Update() { if(Input.GetKeyDown(KeyCode.Space)) { if(stretch) { stretch = false; } else { stretch = true; } } }

function OnPostRender() { if (!mat) { Debug.LogError("Please Assign a material on the inspector"); return; } GL.PushMatrix(); mat.SetPass(0); GL.LoadPixelMatrix(); if(stretch) { GL.Viewport(Rect(0,0,Screen.width,Screen.height)); } else { GL.Viewport(Rect(0,0,Screen.width/2,Screen.height)); } GL.Color(Color.red); GL.Begin(GL.QUADS); GL.Vertex3(0,0,0); GL.Vertex3(0,Screen.height,0); GL.Vertex3(Screen.width,Screen.height,0); GL.Vertex3(Screen.width,0,0); GL.Color(Color.yellow); GL.End(); GL.Begin(GL.TRIANGLES); GL.Vertex3(Screen.width/2,Screen.height/4,1); GL.Vertex3(Screen.width/4,Screen.height/2,1); GL.Vertex3(Screen.width - Screen.width/4,Screen.height/2,1); GL.End(); GL.PopMatrix(); }
using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    public Material mat;
    private bool stretch = false;
    void Update() {
        if (Input.GetKeyDown(KeyCode.Space))
            if (stretch)
                stretch = false;
            else
                stretch = true;
        
    }
    void OnPostRender() {
        if (!mat) {
            Debug.LogError("Please Assign a material on the inspector");
            return;
        }
        GL.PushMatrix();
        mat.SetPass(0);
        GL.LoadPixelMatrix();
        if (stretch)
            GL.Viewport(new Rect(0, 0, Screen.width, Screen.height));
        else
            GL.Viewport(new Rect(0, 0, Screen.width / 2, Screen.height));
        GL.Color(Color.red);
        GL.Begin(GL.QUADS);
        GL.Vertex3(0, 0, 0);
        GL.Vertex3(0, Screen.height, 0);
        GL.Vertex3(Screen.width, Screen.height, 0);
        GL.Vertex3(Screen.width, 0, 0);
        GL.Color(Color.yellow);
        GL.End();
        GL.Begin(GL.TRIANGLES);
        GL.Vertex3(Screen.width / 2, Screen.height / 4, 1);
        GL.Vertex3(Screen.width / 4, Screen.height / 2, 1);
        GL.Vertex3(Screen.width - Screen.width / 4, Screen.height / 2, 1);
        GL.End();
        GL.PopMatrix();
    }
}
import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	public mat as Material

	private stretch as bool = false

	def Update() as void:
		if Input.GetKeyDown(KeyCode.Space):
			if stretch:
				stretch = false
			else:
				stretch = true

	def OnPostRender() as void:
		if not mat:
			Debug.LogError('Please Assign a material on the inspector')
			return
		GL.PushMatrix()
		mat.SetPass(0)
		GL.LoadPixelMatrix()
		if stretch:
			GL.Viewport(Rect(0, 0, Screen.width, Screen.height))
		else:
			GL.Viewport(Rect(0, 0, (Screen.width / 2), Screen.height))
		GL.Color(Color.red)
		GL.Begin(GL.QUADS)
		GL.Vertex3(0, 0, 0)
		GL.Vertex3(0, Screen.height, 0)
		GL.Vertex3(Screen.width, Screen.height, 0)
		GL.Vertex3(Screen.width, 0, 0)
		GL.Color(Color.yellow)
		GL.End()
		GL.Begin(GL.TRIANGLES)
		GL.Vertex3((Screen.width / 2), (Screen.height / 4), 1)
		GL.Vertex3((Screen.width / 4), (Screen.height / 2), 1)
		GL.Vertex3((Screen.width - (Screen.width / 4)), (Screen.height / 2), 1)
		GL.End()
		GL.PopMatrix()