GL.Viewport

설명

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.

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();
    }
}