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Tracking finger move in order to rotate a triangle : tracking is not perfect

- by Laurent BERNABE

I've written a custom view, with the OpenGL_1 technology, in order to let user rotate a red triangle just by dragging it along x axis. (Will give a rotation around Y axis). It works, but there is a bit of latency when dragging from one direction to the other (without releasing the mouse/finger). So it seems that my code is not yet "goal perfect". (I am convinced that no code is perfect in itself). I thought of using a quaternion, but maybe it won't be so usefull : must I really use a Quaternion (or a kind of Matrix) ? I've designed application for Android 4.0.3, but it could fit into Android api 3 (Android 1.5) as well (at least, I think it could). So here is my main layout : activity_main.xml <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" > <com.laurent_bernabe.android.triangletournant3d.MyOpenGLView android:layout_width="match_parent" android:layout_height="match_parent" /> </LinearLayout> Here is my main activity : MainActivity.java package com.laurent_bernabe.android.triangletournant3d; import android.app.Activity; import android.os.Bundle; import android.support.v4.app.NavUtils; import android.view.Menu; import android.view.MenuItem; public class MainActivity extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); } @Override public boolean onCreateOptionsMenu(Menu menu) { getMenuInflater().inflate(R.menu.activity_main, menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { switch (item.getItemId()) { case android.R.id.home: NavUtils.navigateUpFromSameTask(this); return true; } return super.onOptionsItemSelected(item); } } And finally, my OpenGL view MyOpenGLView.java package com.laurent_bernabe.android.triangletournant3d; import java.nio.ByteBuffer; import java.nio.ByteOrder; import java.nio.FloatBuffer; import javax.microedition.khronos.egl.EGLConfig; import javax.microedition.khronos.opengles.GL10; import android.content.Context; import android.graphics.Point; import android.opengl.GLSurfaceView; import android.opengl.GLSurfaceView.Renderer; import android.opengl.GLU; import android.util.AttributeSet; import android.view.MotionEvent; public class MyOpenGLView extends GLSurfaceView implements Renderer { public MyOpenGLView(Context context, AttributeSet attrs) { super(context, attrs); setRenderer(this); } public MyOpenGLView(Context context) { this(context, null); } @Override public boolean onTouchEvent(MotionEvent event) { int actionMasked = event.getActionMasked(); switch(actionMasked){ case MotionEvent.ACTION_DOWN: savedClickLocation = new Point((int) event.getX(), (int) event.getY()); break; case MotionEvent.ACTION_UP: savedClickLocation = null; break; case MotionEvent.ACTION_MOVE: Point newClickLocation = new Point((int) event.getX(), (int) event.getY()); int dx = newClickLocation.x - savedClickLocation.x; angle += Math.toRadians(dx); break; } return true; } @Override public void onDrawFrame(GL10 gl) { gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT); gl.glLoadIdentity(); GLU.gluLookAt(gl, 0f, 0f, 5f, 0f, 0f, 0f, 0f, 1f, 0f ); gl.glRotatef(angle, 0f, 1f, 0f); gl.glColor4f(1f, 0f, 0f, 0f); gl.glVertexPointer(2, GL10.GL_FLOAT, 0, triangleCoordsBuff); gl.glDrawArrays(GL10.GL_TRIANGLES, 0, 3); } @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, 60f, (float) width / height, 0.1f, 10f); gl.glMatrixMode(GL10.GL_MODELVIEW); } @Override public void onSurfaceCreated(GL10 gl, EGLConfig config) { gl.glEnable(GL10.GL_DEPTH_TEST); gl.glClearDepthf(1.0f); gl.glEnableClientState(GL10.GL_VERTEX_ARRAY); buildTriangleCoordsBuffer(); } private void buildTriangleCoordsBuffer() { ByteBuffer buffer = ByteBuffer.allocateDirect(4*triangleCoords.length); buffer.order(ByteOrder.nativeOrder()); triangleCoordsBuff = buffer.asFloatBuffer(); triangleCoordsBuff.put(triangleCoords); triangleCoordsBuff.rewind(); } private float [] triangleCoords = {-1f, -1f, +1f, -1f, +1f, +1f}; private FloatBuffer triangleCoordsBuff; private float angle = 0f; private Point savedClickLocation; } I don't think I really have to give you my manifest file. But I can if you think it is necessary. I've just tested on Emulator, not on real device. So, how can improve the reactivity ? Thanks in advance.

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