UnityGL1-2.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

/* Refered the link
http://ft-lab.ne.jp/cgi-bin-unity/wiki.cgi?page=unity%5Fscript%5Fopengl
*/

public class UnityGL1-2 : MonoBehaviour {

	static Material lineMaterial;
	// Use this for initialization

	static void CreateLineMaterial (){
		if (!lineMaterial){
			// Unity has a built-in shader that is useful for drawing
			// simple colored things.
			Shader shader = Shader.Find ("Hidden/Internal-Colored");
			lineMaterial = new Material (shader);
			lineMaterial.hideFlags = HideFlags.HideAndDontSave;
			// Turn on alpha blending
			lineMaterial.SetInt ("_SrcBlend", (int)UnityEngine.Rendering.BlendMode.SrcAlpha);
			lineMaterial.SetInt ("_DstBlend", (int)UnityEngine.Rendering.BlendMode.OneMinusSrcAlpha);
			// Turn backface culling off
			lineMaterial.SetInt ("_Cull", (int)UnityEngine.Rendering.CullMode.Off);
			// Turn off depth writes
			lineMaterial.SetInt ("_ZWrite", 0);
		}
	}

	public void OnRenderObject (){
		CreateLineMaterial ();
		// Apply the line material
		lineMaterial.SetPass (0);

		GL.PushMatrix ();
		// Set transformation matrix for drawing to
		// match our transform
		GL.MultMatrix (transform.localToWorldMatrix);

		float lineWidth = 100.0f;
		// スクリーン上のラインの太さに変換.
    		float thisWidth = 1.0f / Screen.width * lineWidth * 0.5f;

		GL.Begin (GL.QUADS);
	        GL.Color (Color.red);
	        DrawLine2D(new Vector3(0.0f, 0.0f, 0.0f), new Vector3(0.0f, 0.8f, 0.0f), thisWidth);
	        DrawLine2D(new Vector3(0.0f, 0.8f, 0.0f), new Vector3(0.5f, 0.5f, 0.0f), thisWidth);
	        DrawLine2D(new Vector3(0.5f, 0.5f, 0.0f), new Vector3(0.0f, 0.0f, 0.0f), thisWidth);
    		GL.End();
		GL.PopMatrix ();
	}

	// 太さのある線を描画.
	void DrawLine2D(Vector3 v0, Vector3 v1, float lineWidth) {
		Vector3 n = ((new Vector3(v1.y, v0.x, 0.0f)) - (new Vector3(v0.y, v1.x, 0.0f))).normalized * lineWidth;
		GL.Vertex3(v0.x - n.x, v0.y - n.y, 0.0f);
		GL.Vertex3(v0.x + n.x, v0.y + n.y, 0.0f);
		GL.Vertex3(v1.x + n.x, v1.y + n.y, 0.0f);
		GL.Vertex3(v1.x - n.x, v1.y - n.y, 0.0f);
	}
}