From 34507982780a6d274702fe6d7dce7daa0ea68aad Mon Sep 17 00:00:00 2001
From: Josh Holtrop <jholtrop@gmail.com>
Date: Fri, 9 Nov 2012 21:49:55 -0500
Subject: [PATCH] use an ortho projection matrix to keep the quad square

---
 assets/shaders/vertex.glsl                    |  3 ++-
 .../holtrop/opengltest/MyRenderer.java        | 21 ++++++++++++++++++-
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/assets/shaders/vertex.glsl b/assets/shaders/vertex.glsl
index 9e84a7d..d61ce54 100644
--- a/assets/shaders/vertex.glsl
+++ b/assets/shaders/vertex.glsl
@@ -1,10 +1,11 @@
 
+uniform mat4 projection;
 attribute vec3 pos;
 attribute vec3 color;
 varying vec3 color_i;
 
 void main()
 {
-    gl_Position = vec4(pos * 0.75, 1);
+    gl_Position = projection * vec4(pos * 0.75, 1);
     color_i = color;
 }
diff --git a/src/com/homelinux/holtrop/opengltest/MyRenderer.java b/src/com/homelinux/holtrop/opengltest/MyRenderer.java
index 8f98d5c..b8ae47f 100644
--- a/src/com/homelinux/holtrop/opengltest/MyRenderer.java
+++ b/src/com/homelinux/holtrop/opengltest/MyRenderer.java
@@ -14,6 +14,7 @@ import java.io.InputStream;
 import java.io.InputStreamReader;
 import java.io.BufferedReader;
 import java.io.IOException;
+import android.opengl.Matrix;
 
 public class MyRenderer implements GLSurfaceView.Renderer
 {
@@ -21,6 +22,7 @@ public class MyRenderer implements GLSurfaceView.Renderer
     private final String DBGTAG = "JoshsOpenGL";
     private FloatBuffer m_quad_attrib_buffer;
     private AssetManager m_asset_manager;
+    private float m_proj_matrix[] = new float[16];
 
     public MyRenderer(AssetManager am)
     {
@@ -113,7 +115,6 @@ public class MyRenderer implements GLSurfaceView.Renderer
     {
         GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT);
 
-        GLES20.glUseProgram(m_program);
         checkGLError("glBindBuffer");
         int attr_pos = GLES20.glGetAttribLocation(m_program, "pos");
         int attr_color = GLES20.glGetAttribLocation(m_program, "color");
@@ -137,5 +138,23 @@ public class MyRenderer implements GLSurfaceView.Renderer
     public void onSurfaceChanged(GL10 unused, int width, int height)
     {
         GLES20.glViewport(0, 0, width, height);
+
+        if (width < height)
+        {
+            Matrix.orthoM(m_proj_matrix, 0, -1, 1,
+                    -height / (float) width, height / (float) width, 1, -1);
+        }
+        else
+        {
+            Matrix.orthoM(m_proj_matrix, 0,
+                    -width / (float) height, width / (float) height,
+                    -1, 1, 1, -1);
+        }
+
+        GLES20.glUseProgram(m_program);
+
+        GLES20.glUniformMatrix4fv(
+                GLES20.glGetUniformLocation(m_program, "projection"),
+                1, false, m_proj_matrix, 0);
     }
 }