Question

How would I rotate a view in degrees? I’ve got the following code setting up my view…

                   public class GLLayer extends GLSurfaceView implements SurfaceHolder.Callback,
    Camera.PreviewCallback, Renderer {

int onDrawFrameCounter=1;
int[] cameraTexture;
byte[] glCameraFrame=new byte[256*256]; //size of a texture must be a power of 2
FloatBuffer cubeBuff;
FloatBuffer texBuff;
public float startbear;

public GLLayer(Context c) {
    super(c);

    this.setEGLConfigChooser(8, 8, 8, 8, 16, 0);
    this.setRenderer(this);
    this.getHolder().setFormat(PixelFormat.TRANSPARENT);
}

public void onDrawFrame(GL10 gl) {
    onDrawFrameCounter++;

    gl.glEnable(GL10.GL_TEXTURE_2D);
    gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);

    bindCameraTexture(gl);

    gl.glLoadIdentity();
    GLU.gluLookAt(gl, 0, 0, 4.2f, 0, 0, 0, 0, 1, 0);

    //gl.glRotatef(onDrawFrameCounter,1,0,0); //Rotate the camera image
    //gl.glRotatef((float)Math.sin(onDrawFrameCounter/20.0f)*40,0,1,0); //Rotate the camera image
    //gl.glRotatef((float)Math.cos(onDrawFrameCounter/40.0f)*40,0,0,1); //Rotate the camera image

    gl.glNormal3f(0,0,1);
    gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, 4);          
    gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 4, 4);
    gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 8, 4);
    gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP,12, 4);
    gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP,16, 4);
    gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP,20, 4);
}

public void onSurfaceChanged(GL10 gl, int width, int height) {
    gl.glViewport(0, 0, width, height);

    float ratio = (float) width / height;
    gl.glMatrixMode(GL10.GL_PROJECTION);
    gl.glLoadIdentity();
    gl.glFrustumf(-ratio, ratio, -1, 1, 1, 10);

    gl.glMatrixMode(GL10.GL_MODELVIEW);
    gl.glLoadIdentity();
    GLU.gluLookAt(gl, 0, 0, 4.2f, 0, 0, 0, 0, 1, 0);        
}


public void onSurfaceCreated(GL10 gl, EGLConfig config) {
    startbear = Global.bearing;

    gl.glHint(GL10.GL_PERSPECTIVE_CORRECTION_HINT, GL10.GL_FASTEST);

    gl.glClearColor(0, 0, 0, 0);
    gl.glEnable(GL10.GL_CULL_FACE);
    gl.glShadeModel(GL10.GL_SMOOTH);
    gl.glEnable(GL10.GL_DEPTH_TEST);

    cubeBuff = makeFloatBuffer(camObjCoord);
    texBuff = makeFloatBuffer(camTexCoords);        
    gl.glVertexPointer(3, GL10.GL_FLOAT, 0, cubeBuff);
    gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
    gl.glTexCoordPointer(2, GL10.GL_FLOAT, 0, texBuff);
    gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
}   

/**
 * Generates a texture from the black and white array filled by the onPreviewFrame
 * method.
 */
void bindCameraTexture(GL10 gl) {
    synchronized(this) {
        if (cameraTexture==null)
            cameraTexture=new int[1];
        else
            gl.glDeleteTextures(1, cameraTexture, 0);

        gl.glGenTextures(1, cameraTexture, 0);
        int tex = cameraTexture[0];
        gl.glBindTexture(GL10.GL_TEXTURE_2D, tex);
        gl.glTexImage2D(GL10.GL_TEXTURE_2D, 0, GL10.GL_LUMINANCE, 256, 256,   0, GL10.GL_LUMINANCE, GL10.GL_UNSIGNED_BYTE, ByteBuffer.wrap(glCameraFrame));
        gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MIN_FILTER, GL10.GL_LINEAR);
    }
}

/**
 * This method is called if a new image from the camera arrived. The camera
 * delivers images in a yuv color format. It is converted to a black and white
 * image with a size of 256x256 pixels (only a fraction of the resulting image
 * is used). Afterwards Rendering the frame (in the main loop thread) is started by
 * setting the newFrameLock to true. 
 */
public void onPreviewFrame(byte[] yuvs, Camera camera) {        
    int bwCounter=0;
    int yuvsCounter=0;
    for (int y=0;y<160;y++) {
        System.arraycopy(yuvs, yuvsCounter, glCameraFrame, bwCounter, 240);
        yuvsCounter=yuvsCounter+240;
        bwCounter=bwCounter+256;
    }
}

FloatBuffer makeFloatBuffer(float[] arr) {
    ByteBuffer bb = ByteBuffer.allocateDirect(arr.length*4);
    bb.order(ByteOrder.nativeOrder());
    FloatBuffer fb = bb.asFloatBuffer();
    fb.put(arr);
    fb.position(0);
    return fb;
}

final static float camObjCoord[] = new float[] {
            // FRONT
             -2.0f, -1.5f,  12.0f,
              2.0f, -1.5f,  12.0f,
             -2.0f,  1.5f,  12.0f,
              2.0f,  1.5f,  12.0f,
             // BACK
             -2.0f, -1.5f,  8.0f,
             -2.0f,  1.5f,  8.0f,
              2.0f, -1.5f,  8.0f,
              2.0f,  1.5f,  8.0f,
             // LEFT
             -2.0f, -1.5f,  12.0f,
             -2.0f,  1.5f,  12.0f,
             -2.0f, -1.5f,  8.0f,
             -2.0f,  1.5f,  8.0f,
             // RIGHT
              2.0f, -1.5f,  8.0f,
              2.0f,  1.5f,  8.0f,
              2.0f, -1.5f, 12.0f,
              2.0f,  1.5f, 12.0f,
             // TOP
             -2.0f,  1.5f, 12.0f,
              2.0f,  1.5f, 12.0f,
             -2.0f,  1.5f,  8.0f,
              2.0f,  1.5f,  8.0f,
             // BOTTOM
             -2.0f, -1.5f, 12.0f,
             -2.0f, -1.5f,  8.0f,
              2.0f, -1.5f, 12.0f,
              2.0f, -1.5f,  8.0f,
        };
        final static float camTexCoords[] = new float[] {
            // Camera preview
             0.0f, 0.0f,
             0.9375f, 0.0f,
             0.0f, 0.625f,
             0.9375f, 0.625f,

            // BACK
             0.9375f, 0.0f,
             0.9375f, 0.625f,
             0.0f, 0.0f,
             0.0f, 0.625f,
            // LEFT
             0.9375f, 0.0f,
             0.9375f, 0.625f,
             0.0f, 0.0f,
             0.0f, 0.625f,
            // RIGHT
             0.9375f, 0.0f,
             0.9375f, 0.625f,
             0.0f, 0.0f,
             0.0f, 0.625f,
            // TOP
             0.0f, 0.0f,
             0.9375f, 0.0f,
             0.0f, 0.625f,
             0.9375f, 0.625f,
            // BOTTOM
             0.9375f, 0.0f,
             0.9375f, 0.625f,
             0.0f, 0.0f,
             0.0f, 0.625f        
        };

                  }

I’m looking to change my view in degrees.. how would I do so? I assume I’d use glrotate but how would I? (only on the x axis)

// Just a clarification that I’m in fact looking to do a view transformation so that the world around me would rotate X degrees depending on orientation of the camera device.

Answer 1

You can try rotating the canvas, if you want to rotate the whole view.

canvas.rotate(90); // 90 degrees

If you don’t have canvas, implement the onDraw method that it inherits from View:

onDraw(Canvas canvas) {
  canvas.rotate(90); // 90 degrees
} 

Hopefully this works.