Hi, i'm fairly new to Android & OpenGL, and I'm just messing around, trying to learn.

The thing I am trying to do is this .

You move the ship to the right by pressing on the right side of the screen, and left by pressing on the left side.
The thing I'm trying to achieve is that the ship should always in the center of the screen. Except for when you are close to the edges of the background(like in the image above, you are at the top left side, and then the camera should stop following the ship, and just be still while the ship moves closer to the edges of the background.
So the ship should only be in the center if you far away from the backgrounds edges.

I cannot figure out how to do this..

This is my rendering code:

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   public void drawFrame(GL10 gl) {
      updateScene(gl);
      gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);      
      gl.glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
      
      gl.glMatrixMode(GL10.GL_MODELVIEW);
      gl.glLoadIdentity();
      if(mShip.getX() >= 0 && mShip.getX() <= (mViewWidth/2)) {
         // don't translate
      } else {
                        // Move the camera with the ship.
         gl.glTranslatef(-mShip.getX(),-mShip.getY(),0);
      }
      mBackground.draw(gl);
      
      gl.glPushMatrix();
      if(mShip.goLeft) {
         mShip.mX -= 12.0f;
      }
      if ( mShip.goRight) {
         mShip.mX += 12.0f;
      }
      mShip.draw(gl);   
      gl.glPopMatrix();      
   }

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   public void sizeChanged(GL10 gl, int width, int height) {
      mViewWidth = width;
       mViewHeight = height;

      gl.glMatrixMode(GL10.GL_PROJECTION);
      gl.glLoadIdentity();
      
      gl.glViewport(0, 0, mViewWidth,  mViewHeight);   
       gl.glOrthof(0.0f, mViewWidth, mViewHeight, 0.0f, -1.0f, 1.0f);
      
      gl.glMatrixMode(GL10.GL_MODELVIEW);
      gl.glLoadIdentity();
   }

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   @Override
   public void surfaceCreated(GL10 gl) {
      gl.glClearColor(0.5f, 0.5f, 0.5f, 1);
      gl.glHint(GL10.GL_PERSPECTIVE_CORRECTION_HINT, GL10.GL_FASTEST);
      gl.glShadeModel(GL10.GL_FLAT);
      gl.glDisable(GL10.GL_DEPTH_TEST);
      gl.glEnable(GL10.GL_BLEND);
      gl.glBlendFunc(GL10.GL_ONE, GL10.GL_ONE_MINUS_SRC_ALPHA);
      gl.glEnable(GL10.GL_BLEND);
      gl.glBlendFunc(GL10.GL_SRC_ALPHA, GL10.GL_ONE_MINUS_SRC_ALPHA);
      gl.glShadeModel(GL10.GL_FLAT);
      gl.glEnable(GL10.GL_TEXTURE_2D);
      gl.glViewport(0, 0, mViewWidth,  mViewHeight);
      
      gl.glMatrixMode(GL10.GL_PROJECTION);
      gl.glLoadIdentity();
      gl.glOrthof(0.0f, mViewWidth, mViewHeight, 0.0f, -1.0f, 1.0f);      
      gl.glMatrixMode(GL10.GL_MODELVIEW);
      gl.glLoadIdentity();
      
      mShip.loadGLTexture(gl, mContext, R.drawable.ship);
      mBackground.loadGLTexture(gl, mContext, R.drawable.space);
   }

and here is the ship.java


and this is my Ship.java

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public class Ship extends Renderable {
   private FloatBuffer vertexBuffer;
   private ShortBuffer indexBuffer;
   private FloatBuffer textureBuffer;
   
   private int coordinatesPerVertex = 3;
   private int numberVertices = 4;
   private int numberIndices = 4;
   
   public boolean goLeft = false;
   public boolean goRight = false;
   
   private float[] vertices;
   private int[] textures = new int[1];   
   private float texture[] = {
         0.0f, 1.0f,      // top left
         0.0f, 0.0f,      // bottom left
         1.0f, 1.0f,      // top right
         1.0f, 0.0f      // bottom right
   };
   public void handleInput(float dx, float dy, int sWidth, int sHeight) {
      if(dx > 0 && dx < (sWidth/2)) {
         goLeft = true;
         goRight = false;
      }
      if( dx > (sWidth/2) && dx < sWidth) {
         goLeft = false;
         goRight = true;
      }
   }
   public Ship(int width, int height) {
      mWidth = width;
      mHeight = height;
      
      setX(64);
      setY(64);
      
      vertices = new float[] {       
            0.0f,    mHeight, 0.0f,       
            0.0f,    0.0f,     0.0f,
            mWidth, mHeight, 0.0f,
            mWidth, 0.0f,    0.0f
         };
      
      ByteBuffer vBuffer = ByteBuffer.allocateDirect(numberVertices * coordinatesPerVertex * 4);   
      vBuffer.order(ByteOrder.nativeOrder());   
      
      vertexBuffer = vBuffer.asFloatBuffer(); 
      ByteBuffer iBuffer = ByteBuffer.allocateDirect(numberIndices * 2);   
      
      iBuffer.order(ByteOrder.nativeOrder());   
      indexBuffer = iBuffer.asShortBuffer();
      short[] indices = {0, 1, 2, 3 };   
      vertexBuffer.put(vertices);   
      indexBuffer.put(indices);
      vertexBuffer.position(0);   
      indexBuffer.position(0); 
      
      vBuffer = ByteBuffer.allocateDirect(texture.length * 4);
      vBuffer.order(ByteOrder.nativeOrder());
      textureBuffer = vBuffer.asFloatBuffer();
      textureBuffer.put(texture);
      textureBuffer.position(0);
      
   }
   private void update() {
      
   }
   public void draw(GL10 gl) {
      update();         
      
      gl.glTranslatef(getX(),getY(),0.0f);
      
      
      gl.glBindTexture(GL10.GL_TEXTURE_2D, textures[0]);
      gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
      gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY);      
      gl.glFrontFace(GL10.GL_CW);      
      gl.glVertexPointer(coordinatesPerVertex, GL10.GL_FLOAT, 0, vertexBuffer);
      gl.glTexCoordPointer(2, GL10.GL_FLOAT, 0, textureBuffer);
      gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, vertices.length / 3);
      gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
      gl.glDisableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
   }
   public void loadGLTexture(GL10 gl, Context context, int picture) {      
      Bitmap bitmap = BitmapFactory.decodeResource(context.getResources(),
            picture);
      gl.glGenTextures(1, textures, 0);
      gl.glBindTexture(GL10.GL_TEXTURE_2D, textures[0]);
      
      gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MIN_FILTER, GL10.GL_NEAREST);
      gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MAG_FILTER, GL10.GL_LINEAR);

      GLUtils.texImage2D(GL10.GL_TEXTURE_2D, 0, bitmap, 0);
      bitmap.recycle();
   }
}

Update: Here is the background class.

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public class Background extends Renderable  {
   private FloatBuffer vertexBuffer;
   private ShortBuffer indexBuffer;
   private FloatBuffer textureBuffer;
   
   private int coordinatesPerVertex = 3;
   private int numberVertices = 4;
   private int numberIndices = 4;
   
   private float[] vertices;
   private int[] textures = new int[1];   
   private float texture[] = {
         0.0f, 1.0f,      // top left
         0.0f, 0.0f,      // bottom left
         1.0f, 1.0f,      // top right
         1.0f, 0.0f      // bottom right
   };
   public Background(int width, int height) {
      mWidth = width;
      mHeight = height;
      
      vertices = new float[] {       
            0.0f,    mHeight, 0.0f,       
            0.0f,    0.0f,     0.0f,       
            mWidth, mHeight, 0.0f,
            mWidth, 0.0f,    0.0f
         };
      
      ByteBuffer vBuffer = ByteBuffer.allocateDirect(numberVertices * coordinatesPerVertex * 4);   
      vBuffer.order(ByteOrder.nativeOrder());   
      
      vertexBuffer = vBuffer.asFloatBuffer(); 
      ByteBuffer iBuffer = ByteBuffer.allocateDirect(numberIndices * 2);   
      
      iBuffer.order(ByteOrder.nativeOrder());   
      indexBuffer = iBuffer.asShortBuffer();
      short[] indices = {0, 1, 2, 3 };   
      vertexBuffer.put(vertices);   
      indexBuffer.put(indices);
      vertexBuffer.position(0);   
      indexBuffer.position(0); 
      
      vBuffer = ByteBuffer.allocateDirect(texture.length * 4);
      vBuffer.order(ByteOrder.nativeOrder());
      textureBuffer = vBuffer.asFloatBuffer();
      textureBuffer.put(texture);
      textureBuffer.position(0);
      
   }


   private void update() {
      
   }
   public void draw(GL10 gl) {
      update();
      gl.glPushMatrix();      
      
      gl.glTranslatef(getX(),getY(),0.0f);
      
      
      gl.glBindTexture(GL10.GL_TEXTURE_2D, textures[0]);
      gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
      gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY);      
      gl.glFrontFace(GL10.GL_CW);      
      gl.glVertexPointer(coordinatesPerVertex, GL10.GL_FLOAT, 0, vertexBuffer);
      gl.glTexCoordPointer(2, GL10.GL_FLOAT, 0, textureBuffer);
      gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, vertices.length / 3);
      gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
      gl.glDisableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
      
      gl.glPopMatrix();
   }
   public void loadGLTexture(GL10 gl, Context context, int picture) {      
      Bitmap bitmap = BitmapFactory.decodeResource(context.getResources(),
            picture);
      gl.glGenTextures(1, textures, 0);
      gl.glBindTexture(GL10.GL_TEXTURE_2D, textures[0]);
      
      gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MIN_FILTER, GL10.GL_NEAREST);
      gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MAG_FILTER, GL10.GL_LINEAR);

      GLUtils.texImage2D(GL10.GL_TEXTURE_2D, 0, bitmap, 0);
      bitmap.recycle();
   }
}

Any help at all is appreciated!
I have tried searching for tutorials and documentation...Just can't make it work!

Thanks!

Hi peaver,
is your problem still unsolved?
If so would you also post the draw method of your Background class.

Hi, yes, it is still unsolved
updated the original post with the background class.

Hi Peaver,

Have you tried getting the display size of the screen? If you're not familiar here's how to get the height and width of the screen.



Divide it by 2 for you to have the center of the screen then subtract the ((screenheight) - (shipheight / 2)) and ((screenwidth) - (shipwidth / 2)) the result that you've get will be the X and Y of the ship. This is just an Idea hope this will help solve your problem.

Hi ruelblapid,
I've tried implementing the code you posted, but that just gives me the same numbers. 427, am I missing something? The screenwidth is not changing, and the ship width is not changing