Android OpenGL passing OnTouch event value

Question

I'm having problem. I don't know how to pass the value x and y in the OnTouch method to the private final class MyRenderer and update the OnDrawFrame tex.draw(,x,y,,,) function x and y value to be able to translate the object I want to move with my finger.

Any guidance with be appreciated~

public class Stage extends GLSurfaceView{

// Stage width and height
private float w, h;

// Screen width and height
private int screenWidth, screenHeight;

// Our native vertex buffer
private FloatBuffer vertexBuffer;

private Texture tex;

@Override
public boolean onTouchEvent(MotionEvent event) {
    final int action = event.getAction() & MotionEvent.ACTION_MASK;
    float x, y;
    int pointerIndex;
    int pointerId;

    if (action == MotionEvent.ACTION_DOWN) {
        pointerId = event.getPointerId(0);
        x = event.getX();
        y = event.getY();
        pointerIndex = 0;
    } else {
        pointerIndex = event.getActionIndex();
        pointerId = event.getPointerId(pointerIndex);
        x = event.getX(pointerIndex);
        y = event.getY(pointerIndex);
    }
    Log.v("this X", String.valueOf(x));
    Log.v("this Y", String.valueOf(y));

    return true;
}

public Stage(Context context, AttributeSet attrs) {
    super(context, attrs);
    setEGLConfigChooser(8, 8, 8, 8, 0, 0);
    setRenderer(new MyRenderer());
    setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY);
    float vertices[] = {
            -0.5f, -0.5f,  0.0f,  // 0. left-bottom
            0.5f, -0.5f,  0.0f,  // 1. right-bottom
            -0.5f,  0.5f,  0.0f,  // 2. left-top
            0.5f,  0.5f,  0.0f   // 3. right-top
    };

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

    tex = new Texture(R.drawable.kdk);

}

private final class MyRenderer implements GLSurfaceView.Renderer {

    public final void onDrawFrame(GL10 gl) {

        gl.glClear(GLES10.GL_COLOR_BUFFER_BIT);
        gl.glLoadIdentity();
        tex.prepare(gl, GL10.GL_CLAMP_TO_EDGE);
        gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuffer);
        tex.draw(gl, w / 2, h / 2, tex.getWidth(), tex.getHeight(), 0);

    }

    public final void onSurfaceChanged(GL10 gl, int width, int height) {
        gl.glClearColor(0, 0, 0, 0);

        if(width > height) {
            h = 600;
            w = width * h / height;
        } else {
            w = 600;
            h = height * w / width;
        }
        screenWidth = width;
        screenHeight = height;

        gl.glViewport(0, 0, screenWidth, screenHeight);
        gl.glMatrixMode(GL10.GL_PROJECTION);
        gl.glLoadIdentity();
        gl.glOrthof(0, w, h, 0, -1, 1);
        gl.glMatrixMode(GL10.GL_MODELVIEW);
        gl.glLoadIdentity();
    }

    public final void onSurfaceCreated(GL10 gl, EGLConfig config) {
        // Set up alpha blending
        gl.glEnable(GL10.GL_ALPHA_TEST);
        gl.glEnable(GL10.GL_BLEND);
        gl.glBlendFunc(GL10.GL_ONE, GL10.GL_ONE_MINUS_SRC_ALPHA);

        // We are in 2D. Why needs depth?
        gl.glDisable(GL10.GL_DEPTH_TEST);

        // Enable vertex arrays (we'll use them to draw primitives).
        gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);

        // Enable texture coordination arrays.
        gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY);

        tex.load(getContext());
    }

}

}

Other coding

How to apply drag drop and scale in Android OpenGL ES

Answer 1

To achieve this you will have to add a MyRenderer attribute to your Stage class.

This solution will work but it is maybe not the best so fell free to comment.

---

1. You need to change the definition of your inner class MyRenderer by removing the final statement :

   EDIT : I am not sure about this one because final class will have all its methods set to final but maybe not the attributes. If someone can answer it I'll be glade to read it.

   private final class MyRenderer implements GLSurfaceView.Renderer

   To

   private class MyRenderer implements GLSurfaceView.Renderer

---

2. In your Stage class :

   public class Stage extends GLSurfaceView {
   
       // Stage width and height
       private float w, h;
   
       ...
   
       // The renderer
       MyRenderer mRenderer;
   
       ...
   
       public Stage(Context context, AttributeSet attrs) {
   
           mRenderer = new MyRenderer();
   
           super(context, attrs);
           setEGLConfigChooser(8, 8, 8, 8, 0, 0);
   
           setRenderer(mRenderer);
   
           ...
       }
   }
   

---

3. Add the setters to your MyRenderer class :

   private class MyRenderer implements GLSurfaceView.Renderer {
   
       float xPos;
       float yPos;
   
       // ...
   
       public void setX(float x) {
           xPos = x;
       }
   
       public void setY(float y) {
           yPos = y;
       }
   
       public void setXY(float x, float y) {
           xPos = x;
           yPos = y;
       }
   }
   

---

4. Finally set these values in the OnTouch method.

---

Edit :

To set the xPos and yPos default value :

private class MyRenderer implements GLSurfaceView.Renderer {

    float xPos;
    float yPos;

    boolean initialised = false;

    ...

    public final void onSurfaceChanged(GL10 gl, int width, int height) {

        if (!initialised) {
            xPos = width /2;
            yPos = height / 2;
            initialised = true;
        }

        ...
    }

    ...
}

---

EDIT 2 :

To avoid race condition set the X and Y value at the same time with one function. When entering the method it will create temporary variable with the value passed in parameters. This will ensure that the x and y value passed are from the same Event.

private class MyRenderer implements GLSurfaceView.Renderer {

    float xPos;
    float yPos;

    // ...


    public void setXY(float x, float y) {
        xPos = x;
        yPos = y;
    }
}