Question

I am just getting started with using opengl in my apps and I get it fine =) but I’ve hit a brick wall recently as I have been attempting to work out methods of user input.
I decided to start with a simple process that draws a square to the screen at the position you touch the screen. Unfortunatly the app doesn’t seem to register the input.

Here is my code:

The app opens with this activity >>

import android.app.Activity;
import android.opengl.GLSurfaceView;
import android.os.Bundle;
import android.view.Window;
import android.view.WindowManager;

public class Practice extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    this.requestWindowFeature(Window.FEATURE_NO_TITLE);
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, 
            WindowManager.LayoutParams.FLAG_FULLSCREEN);
    GLSurfaceView view = new GLSurfaceView (this);
    view.setRenderer(new GLSurfaceRenderer());
    setContentView(view);    
}
}

This initializes a full screen SurfaceView.

Next the renderer

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

import android.opengl.GLU;
import android.opengl.GLSurfaceView.Renderer;
import android.view.MotionEvent;


public class GLSurfaceRenderer implements Renderer{

private FlatColoredSquare Square;
private float setx = 0;
private float sety = 0; 


    public GLSurfaceRenderer () {   
    Square = new FlatColoredSquare();

}
    public boolean onTouchEvent (MotionEvent event, GL10 gl){
        if (event.getAction() == MotionEvent.ACTION_UP){    
        gl.glPushMatrix();
        gl.glTranslatef(event.getX(), event.getY(), -10);
        Square.draw(gl);
        gl.glPopMatrix();
        }

        return true;

    }



 @Override
public void onDrawFrame(GL10 gl) {
         gl.glClear(GL10.GL_COLOR_BUFFER_BIT |
            GL10.GL_DEPTH_BUFFER_BIT);
         gl.glLoadIdentity();

    gl.glPushMatrix();
    gl.glTranslatef(setx, sety, -10);
    Square.draw(gl);        
    gl.glPopMatrix();
         }






@Override
public void onSurfaceChanged(GL10 gl, int width, int height) {
    gl.glViewport(0, 0, width, height);
    gl.glMatrixMode(GL10.GL_PROJECTION);
    gl.glLoadIdentity();
    GLU.gluPerspective(gl, 45.0f, (float)width / (float)height, 0.1f, 100f);
    gl.glMatrixMode(GL10.GL_MODELVIEW);
    gl.glLoadIdentity();

}

@Override
public void onSurfaceCreated(GL10 gl, EGLConfig config) {
    gl.glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    gl.glShadeModel(GL10.GL_SMOOTH);
    gl.glClearDepthf(1.0f);
    gl.glEnable(GL10.GL_DEPTH_TEST);
    gl.glDepthFunc(GL10.GL_LEQUAL);
    gl.glHint(GL10.GL_PERSPECTIVE_CORRECTION_HINT, GL10.GL_NICEST);

}



}

As you can see there is an onTouchEvent that gets the coordinates of the event and sets them to the floats at the top. The draw method then uses these coordinates to set the position of the square. I don’t think the draw method here updates enough to redraw the square. How can I set the draw method to update the square onTouch? As well as trying to set the square to draw from inside the onTouch method I have also left it blank like:

public boolean onTouchEvent (MotionEvent event){
        if (event.getAction() == MotionEvent.ACTION_UP){    
        setx = event.getX();
        sety = event.getY();
        }

        return true;

    }

Both of these return the same results =(
So am I doing the onTouchEvent wrong?
or do I have to force the draw method to update somehow?
and how would I implement this properly?

Thank you for your time

EDIT:

Managed to get the code to register an onTouchEvent by moving the method over to the Practice class.

EDIT: Made some more improvements code now works properly to an extent but instead of redrawing the square in the desired place I instead get a blank cleared screen.

Here is edited Practice

import android.app.Activity;
import android.opengl.GLSurfaceView;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.Window;
import android.view.WindowManager;
import android.app.ui.GLSurfaceRenderer;



public class Practice extends Activity {
private GLSurfaceRenderer glSurfaceRenderer;
public static float setx;
public static float sety;




/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    this.requestWindowFeature(Window.FEATURE_NO_TITLE);
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, 
            WindowManager.LayoutParams.FLAG_FULLSCREEN);
    GLSurfaceView view = new GLSurfaceView (this);
    view.setRenderer(glSurfaceRenderer = new GLSurfaceRenderer());

    setContentView(view);
}
@Override
public synchronized boolean onTouchEvent (MotionEvent event){

        if (event.getAction() == MotionEvent.ACTION_UP){
            glSurfaceRenderer.randomMethod(event);
    }

    return true;

}
}

And edited Renderer Class

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

import android.opengl.GLU;
import android.opengl.GLSurfaceView.Renderer;
import android.view.MotionEvent;




public class GLSurfaceRenderer implements Renderer{
private float setx; 
private float sety; 

private FlatColoredSquare square;


    public GLSurfaceRenderer () {   
    square = new FlatColoredSquare();


}

    public synchronized void randomMethod(MotionEvent event){
        setx = event.getX();
        sety = event.getY();
    }



@Override
public void onDrawFrame(GL10 gl) {
         gl.glClear(GL10.GL_COLOR_BUFFER_BIT |
            GL10.GL_DEPTH_BUFFER_BIT);
         gl.glLoadIdentity();


             gl.glPushMatrix();
    gl.glTranslatef(setx, sety, -10);
    square.draw(gl);        
    gl.glPopMatrix();

         }








@Override
public void onSurfaceChanged(GL10 gl, int width, int height) {
    gl.glViewport(0, 0, width, height);
    gl.glMatrixMode(GL10.GL_PROJECTION);
    gl.glLoadIdentity();
    GLU.gluPerspective(gl, 45.0f, (float)width / (float)height, 0.1f, 100f);
    gl.glMatrixMode(GL10.GL_MODELVIEW);
    gl.glLoadIdentity();

}

@Override
public void onSurfaceCreated(GL10 gl, EGLConfig config) {
    gl.glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    gl.glShadeModel(GL10.GL_SMOOTH);
    gl.glClearDepthf(1.0f);
    gl.glEnable(GL10.GL_DEPTH_TEST);
    gl.glDepthFunc(GL10.GL_LEQUAL);
    gl.glHint(GL10.GL_PERSPECTIVE_CORRECTION_HINT, GL10.GL_NICEST);

}



}

Any ideas?
Here is the square code

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;
import java.nio.ShortBuffer;

import javax.microedition.khronos.opengles.GL10;

public class FlatColoredSquare {
private float vertices[] = {
        -1.0f, 1.0f, 0.0f,
        -1.0f, -1.0f, 0.0f,
        1.0f, -1.0f, 0.0f,
        1.0f, 1.0f, 0.0f
};

private short indices[] = {0, 1, 2, 0, 2, 3,};

private FloatBuffer vertexBuffer;

private ShortBuffer indexBuffer;


public FlatColoredSquare() {
    ByteBuffer vbb = ByteBuffer.allocateDirect(vertices.length*4);
    vbb.order(ByteOrder.nativeOrder());
    vertexBuffer = vbb.asFloatBuffer();
    vertexBuffer.put(vertices);
    vertexBuffer.position(0);

    ByteBuffer ibb = ByteBuffer.allocateDirect(indices.length*2);
    ibb.order(ByteOrder.nativeOrder());
    indexBuffer = ibb.asShortBuffer();
    indexBuffer.put(indices);
    indexBuffer.position(0);
}

public void draw(GL10 gl) {
    gl.glColor4f(0.0f, 1.0f, 0.0f, 0.0f);
    gl.glFrontFace(GL10.GL_CCW);
    gl.glEnable(GL10.GL_CULL_FACE);
    gl.glCullFace(GL10.GL_BACK);

    gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
    gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuffer);
    gl.glDrawElements(GL10.GL_TRIANGLES, indices.length, 
                      GL10.GL_UNSIGNED_SHORT, indexBuffer);
    gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
    gl.glDisable(GL10.GL_CULL_FACE);
}

}

Answer 1

Two problems here.

1) You are using your own, custom onTouchEvent() method. Your method onTouchEvent() with the arguments MotionEvent event, GL10 gl has no official support in the SDK.

2) You are modifying data that explicitly are running in another thread. The touch event’s threads differs from the GL thread.

Your solution is simple. Override onTouchEvent(MotionEvent event) (or set an onTouchListener to your GLSurfaceView class) in your activity class and call a method (which should be declared as synchronized) in your view class within it. An alternative is to update logic in a different thread, however, that is up to you to decide.