GL.Viewport

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 ExampleClass : 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();
    }
}