Skip to content

Most visited

Recently visited


Responding to Touch Events

This lesson teaches you to

  1. Setup a Touch Listener
  2. Expose the Rotation Angle
  3. Apply Rotation

You should also read

Download the sample

Making objects move according to a preset program like the rotating triangle is useful for getting some attention, but what if you want to have users interact with your OpenGL ES graphics? The key to making your OpenGL ES application touch interactive is expanding your implementation of GLSurfaceView to override the onTouchEvent() to listen for touch events.

This lesson shows you how to listen for touch events to let users rotate an OpenGL ES object.

Setup a Touch Listener

In order to make your OpenGL ES application respond to touch events, you must implement the onTouchEvent() method in your GLSurfaceView class. The example implementation below shows how to listen for MotionEvent.ACTION_MOVE events and translate them to an angle of rotation for a shape.

private final float TOUCH_SCALE_FACTOR = 180.0f / 320;
private float mPreviousX;
private float mPreviousY;

public boolean onTouchEvent(MotionEvent e) {
    // MotionEvent reports input details from the touch screen
    // interested in events where the touch position changed.

    float x = e.getX();
    float y = e.getY();

    switch (e.getAction()) {
        case MotionEvent.ACTION_MOVE:

            float dx = x - mPreviousX;
            float dy = y - mPreviousY;

            // reverse direction of rotation above the mid-line
            if (y > getHeight() / 2) {
              dx = dx * -1 ;

            if (x < getWidth() / 2) {
              dy = dy * -1 ;

                    mRenderer.getAngle() +
                    ((dx + dy) * TOUCH_SCALE_FACTOR));

    mPreviousX = x;
    mPreviousY = y;
    return true;

Notice that after calculating the rotation angle, this method calls requestRender() to tell the renderer that it is time to render the frame. This approach is the most efficient in this example because the frame does not need to be redrawn unless there is a change in the rotation. However, it does not have any impact on efficiency unless you also request that the renderer only redraw when the data changes using the setRenderMode() method, so make sure this line is uncommented in the renderer:

public MyGLSurfaceView(Context context) {

Expose the Rotation Angle

The example code above requires that you expose the rotation angle through your renderer by adding a public member. Since the renderer code is running on a separate thread from the main user interface thread of your application, you must declare this public variable as volatile. Here is the code to declare the variable and expose the getter and setter pair:

public class MyGLRenderer implements GLSurfaceView.Renderer {

    public volatile float mAngle;

    public float getAngle() {
        return mAngle;

    public void setAngle(float angle) {
        mAngle = angle;

Apply Rotation

To apply the rotation generated by touch input, comment out the code that generates an angle and add mAngle, which contains the touch input generated angle:

public void onDrawFrame(GL10 gl) {
    float[] scratch = new float[16];

    // Create a rotation for the triangle
    // long time = SystemClock.uptimeMillis() % 4000L;
    // float angle = 0.090f * ((int) time);
    Matrix.setRotateM(mRotationMatrix, 0, mAngle, 0, 0, -1.0f);

    // Combine the rotation matrix with the projection and camera view
    // for the matrix multiplication product to be correct.

    // Draw triangle

When you have completed the steps described above, run the program and drag your finger over the screen to rotate the triangle:

Figure 1. Triangle being rotated with touch input (circle shows touch location).



* Required Fields


WeChat에서 Google Developers 팔로우하기

Browse this site in ?



This class requires API level or higher



Take a short survey?