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Apps (SOLVED)(OpenGL) Everything looks scaled/ translated along Z axis


Apr 8, 2013
Good morning,

I'm rather new to OpenGL programming, so please forgive me if this is easy to answer.

My goal is to display 3 line segments of unit lenght at the origin that each point down an axis.

Everything in my app looks translated and / or scaled along the Z axis, but I cannot find the cause.

Here's my rendering code:

package nl.wernerkroneman.tunnel.flyer;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;
import java.util.ArrayList;

import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.opengles.GL10;

import android.opengl.GLES20;
import android.opengl.GLSurfaceView;
import android.opengl.Matrix;
import android.os.SystemClock;

public class GameManager implements GLSurfaceView.Renderer {
    private float[] mMVPMatrix = new float[16];
    private final float[] mProjMatrix = new float[16];
    private final float[] mViewMatrix = new float[16];
    private int mGLProgram;
    private int mColorHandle;
    private int muMVPMatrixHandle;
    static final int COORDS_PER_VERTEX = 3;
    private final int vertexStride = COORDS_PER_VERTEX * 4; // bytes per vertex
    final float[] axismarkerPoints = {0f,0f,0f, 1f,0f,0f, 0f,0f,0f, 0f,1f,0f, 0f,0f,0f, 0f,0f,1f};
    FloatBuffer axitMarkBuf;
    float[] speed;
    private final String vertexShaderCode =
            // This matrix member variable provides a hook to manipulate
            // the coordinates of the objects that use this vertex shader
            "uniform mat4 uMVPMatrix;" +

            "attribute vec4 vPosition;" +
            "void main() {" +
            // the matrix must be included as a modifier of gl_Position
            "  gl_Position = vPosition * uMVPMatrix;" +

    private final String fragmentShaderCode = "precision mediump float;"
        "uniform vec4 vColor;" +
        "void main() {" +
        "  gl_FragColor = vColor;" +

    private ArrayList<TunnelSection> mTunnelSections;
    private long lastUpdate;

    public void onSurfaceCreated(GL10 unused, EGLConfig config) {
        lastUpdate = System.currentTimeMillis();
        speed = new float[]{0f,0f,0f};
        // prepare shaders and OpenGL program
        int vertexShader = GameManager.loadShader(GLES20.GL_VERTEX_SHADER,
        int fragmentShader = GameManager.loadShader(GLES20.GL_FRAGMENT_SHADER,

        mGLProgram = GLES20.glCreateProgram();             // create empty OpenGL Program
        GLES20.glAttachShader(mGLProgram, vertexShader);   // add the vertex shader to program
        GLES20.glAttachShader(mGLProgram, fragmentShader); // add the fragment shader to program
        GLES20.glLinkProgram(mGLProgram);                  // create OpenGL program executables
        // Set the background frame color
        GLES20.glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
        mTunnelSections = new ArrayList<TunnelSection>(1);
        TunnelSection previous = null;
        for (int index=0;index<4;index++){
            TunnelSection newSection = new TunnelSection(this,previous);
            previous = newSection;
        // initialize vertex byte buffer for shape coordinates
        ByteBuffer bb = ByteBuffer.allocateDirect(
                // (number of coordinate values * 4 bytes per float)
                axismarkerPoints.length * 4);
        // use the device hardware's native byte order
        // create a floating point buffer from the ByteBuffer
        axitMarkBuf = bb.asFloatBuffer();
        // add the coordinates to the FloatBuffer
        // set the buffer to read the first coordinate

    public void onDrawFrame(GL10 unused) {
        // Draw background color
        float offsetX = android.util.FloatMath.sin(SystemClock.uptimeMillis()/1000.f) * 10f;
        float offsetY = android.util.FloatMath.cos(SystemClock.uptimeMillis()/1000.f) * 10f;
        // Set the camera position (View matrix)
        Matrix.setLookAtM(mViewMatrix,0, offsetX, 0f, offsetY, 0f, 0f, 0f, 0f, 1f, 0f);

        // Calculate the projection and view transformation
        Matrix.multiplyMM(mMVPMatrix, 0, mProjMatrix, 0, mViewMatrix, 0);
        //mMVPMatrix = mViewMatrix;
        //for (int index=0; index<mTunnelSections.size(); index++){

    public void onSurfaceChanged(GL10 unused, int width, int height) {
        // Adjust the viewport based on geometry changes,
        // such as screen rotation
        GLES20.glViewport(0, 0, width, height);
        float ratio = (float) width /  height;
        // this projection matrix is applied to object coordinates
        // in the onDrawFrame() method
        Matrix.frustumM(mProjMatrix, 0, -ratio, ratio, -1, 1, 2, 50);


    public static int loadShader(int type, String shaderCode){

        // create a vertex shader type (GLES20.GL_VERTEX_SHADER)
        // or a fragment shader type (GLES20.GL_FRAGMENT_SHADER)
        int shader = GLES20.glCreateShader(type);

        // add the source code to the shader and compile it
        GLES20.glShaderSource(shader, shaderCode);

        return shader;
    void update(){
        float deltaSecs = (lastUpdate - System.currentTimeMillis())/1000f;
        lastUpdate = System.currentTimeMillis();
        //speed = new float[]{speed[0],speed[1],speed[2]};
        for (int index=0; index<mTunnelSections.size(); index++){
    void drawAxisMarker(){
        // Add program to OpenGL environment
        // get handle to vertex shader's vPosition member
        int mPositionHandle = GLES20.glGetAttribLocation(mGLProgram, "vPosition");
        // get handle to shape's transformation matrix
        int muMVPMatrixHandle = GLES20.glGetUniformLocation(mGLProgram, "uMVPMatrix");
        GLES20.glUniformMatrix4fv(muMVPMatrixHandle, 1, false, mMVPMatrix, 0);
        /* ---------- RING ---------- */

        // Prepare the triangle coordinate data
        GLES20.glVertexAttribPointer(mPositionHandle, COORDS_PER_VERTEX,
                                     GLES20.GL_FLOAT, false,
                                     vertexStride, axitMarkBuf);

        // get handle to fragment shader's vColor member
        mColorHandle = GLES20.glGetUniformLocation(mGLProgram, "vColor");
        float[] color = new float[]{1f,0,1f,1f};
        // Set color for drawing the triangle
        GLES20.glUniform4fv(mColorHandle, 1, color, 0);

        // Draw the triangle
        GLES20.glDrawArrays(GLES20.GL_LINES, 0, 6);

Note that the code refers to "Tunnel Sections". Those are for later and currently don't do anything.


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