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.

using UnityEngine;

public class Example : MonoBehaviour
{
    // 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
    Material mat;
    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();
    }
}