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POOpenGL rotating problem
 

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  1. POOpenGL rotating problem
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    <p>I'm learning Java and OpenGL ES for Android by reading tutorials and applying what I already know. And I have now hit a brick wall when it comes to rotating an object.</p> <p>Rotating a cube by touching the screen is no problem. But if I rotate the cube 180 degrees up or down, then when I now try to rotate the cube left or right it is inverted. I know why this is happening but I cannot find a solution.</p> <p>The code is below if some want to test it:</p> <p>File "Rotating.java":</p> <pre><code>package com.test.opengl; import android.app.Activity; import android.os.Bundle; import android.view.Window; import android.view.WindowManager; public class Rotating extends Activity { private GLControlView glControlView; @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 ); glControlView = new GLControlView( this ); setContentView( glControlView ); } } </code></pre> <p>File "GLControlView.java":</p> <pre><code>package com.test.opengl; import javax.microedition.khronos.egl.EGLConfig; import javax.microedition.khronos.opengles.GL10; import android.content.Context; import android.opengl.GLSurfaceView; import android.opengl.GLU; import android.opengl.GLSurfaceView.Renderer; import android.view.MotionEvent; public class GLControlView extends GLSurfaceView implements Renderer { private Context context; private float xPrevious, yPrevious; private float xRotation = 0.0f, yRotation = 0.0f; private SimpleCubeObject cubeObject; public GLControlView( Context context ) { super( context ); this.context = context; this.setRenderer( this ); this.requestFocus(); this.setFocusableInTouchMode( true ); cubeObject = new SimpleCubeObject(); } public void onSurfaceCreated( GL10 gl, EGLConfig config ) { gl.glClearColor( 0.0f, 0.0f, 0.0f, 0.5f ); 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 ); } public void onDrawFrame( GL10 gl ) { gl.glClear( GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT ); gl.glLoadIdentity(); gl.glTranslatef( 0.0f, 0.0f, -10.0f ); gl.glPushMatrix(); gl.glRotatef( xRotation, 1.0f, 0.0f, 0.0f ); gl.glRotatef( yRotation, 0.0f, 1.0f, 0.0f ); gl.glPushMatrix(); cubeObject.draw( gl ); gl.glPopMatrix(); gl.glPopMatrix(); } 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, 100.0f ); gl.glMatrixMode( GL10.GL_MODELVIEW ); gl.glLoadIdentity(); } @Override public boolean onTouchEvent( MotionEvent event ) { float xEvent = event.getX(); float yEvent = event.getY(); switch( event.getAction() ) { case MotionEvent.ACTION_DOWN: { xPrevious = xEvent; yPrevious = yEvent; return true; } case MotionEvent.ACTION_MOVE: { float xDelta = xEvent - xPrevious; float yDelta = yEvent - yPrevious; xRotation += ( yDelta * 0.5f ); yRotation += ( xDelta * 0.5f ); xPrevious = xEvent; yPrevious = yEvent; return true; } default: return super.onTouchEvent( event ); } } } </code></pre> <p>File "SimpleCubeObject.java":</p> <pre><code>package com.test.opengl; import java.nio.ByteBuffer; import java.nio.ByteOrder; import java.nio.FloatBuffer; import java.nio.ShortBuffer; import javax.microedition.khronos.opengles.GL10; public class SimpleCubeObject { private int[] textures = new int[ 1 ]; private float[] colors = { 0.0f, 0.0f, 0.0f, 1.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f, 1.0f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f, 1.0f, 1.0f, 0.0f, 1.0f, 1.0f, 0.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 0.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f }; private short[] indices = { 0, 1, 2, 0, 2, 3, 1, 5, 6, 1, 6, 2, 2, 6, 7, 2, 7, 3, 3, 7, 4, 3, 4, 0, 0, 4, 5, 0, 5, 1, 7, 6, 5, 7, 5, 4 }; private float[] vertices = { -1.0f, 1.0f, -1.0f, -1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, -1.0f, -1.0f, -1.0f, -1.0f, -1.0f, -1.0f, 1.0f, 1.0f, -1.0f, 1.0f, 1.0f, -1.0f, -1.0f }; private FloatBuffer colorBuffer; private ShortBuffer indexBuffer; private FloatBuffer vertexBuffer; public SimpleCubeObject() { ByteBuffer cbb = ByteBuffer.allocateDirect( colors.length * 4 ); cbb.order( ByteOrder.nativeOrder() ); colorBuffer = cbb.asFloatBuffer(); colorBuffer.put( colors ); colorBuffer.position( 0 ); ByteBuffer ibb = ByteBuffer.allocateDirect( indices.length * 2 ); ibb.order( ByteOrder.nativeOrder() ); indexBuffer = ibb.asShortBuffer(); indexBuffer.put( indices ); indexBuffer.position( 0 ); ByteBuffer vbb = ByteBuffer.allocateDirect( vertices.length * 4 ); vbb.order( ByteOrder.nativeOrder() ); vertexBuffer = vbb.asFloatBuffer(); vertexBuffer.put( vertices ); vertexBuffer.position( 0 ); } public void draw( GL10 gl ) { gl.glFrontFace( GL10.GL_CCW ); gl.glEnable( GL10.GL_CULL_FACE ); gl.glCullFace( GL10.GL_BACK ); gl.glBindTexture( GL10.GL_TEXTURE_2D, textures[ 0 ] ); gl.glEnableClientState( GL10.GL_COLOR_ARRAY ); gl.glEnableClientState( GL10.GL_TEXTURE_COORD_ARRAY ); gl.glColorPointer( 4, GL10.GL_FLOAT, 0, colorBuffer ); 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.glDisableClientState( GL10.GL_COLOR_ARRAY ); gl.glDisable( GL10.GL_CULL_FACE ); } } </code></pre> <p>I sure hope someone can help me with this. I believe, as always, that the solution is simple and easy - it is just me who can't see it right now.</p>
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