GL.LoadOrtho

Description

Helper function to set up an orthograhic projection.

Loads an orthographic projection into the projection matrix and loads an identity into the model and view matrices.

The resulting projection performs the following mappings:
1. x = 0..1 to x = -1..1 (left..right)
2. y = 0..1 to y = -1..1 (bottom..top)
3. z = 1..-100 to z = -1..1 (near..far)

This is equivalent to the following operations:

using UnityEngine;

public class Example : MonoBehaviour
{
    void OnPostRender()
    {
        // ...

        GL.LoadOrtho();

        // is equivalent to:

        GL.LoadIdentity();
        var proj = Matrix4x4.Ortho(0, 1, 0, 1, -1, 100);
        GL.LoadProjectionMatrix(proj);

        // ...
    }
}

Changing the model, view or projection matrices overrides the current rendering matrices. It is good practice to save and restore these matrices using GL.PushMatrix and GL.PopMatrix.

using UnityEngine;

public class Example : MonoBehaviour
{
    // Draws a triangle under an already drawn triangle
    Material mat;

    void OnPostRender()
    {
        if (!mat)
        {
            Debug.LogError("Please Assign a material on the inspector");
            return;
        }
        GL.PushMatrix();
        mat.SetPass(0);
        GL.LoadOrtho();
        GL.Color(Color.red);
        GL.Begin(GL.TRIANGLES);
        GL.Vertex3(0.25f, 0.1351f, 0);
        GL.Vertex3(0.25f, 0.3f, 0);
        GL.Vertex3(0.5f, 0.3f, 0);
        GL.End();

        GL.Color(Color.yellow);
        GL.Begin(GL.TRIANGLES);
        GL.Vertex3(0.5f, 0.25f, -1);
        GL.Vertex3(0.5f, 0.1351f, -1);
        GL.Vertex3(0.1f, 0.25f, -1);
        GL.End();

        GL.PopMatrix();
    }
}

Additional resources: GL.LoadProjectionMatrix, Matrix4x4.Ortho.