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.
