Drawing 2D on a GLSurfaceView

Question

I am attempting to draw a 2D square on a GLSurfaceView in 2D mode. I can draw the object in 3D mode and have tested that the square is out in 3D space. I then try to configure the matrix for 2d drawing and when I attempt to draw my object nothing appears.

My GLSurfaceView instance implements GLSurfaceView.Renderer.

I've broken the setup into two functions:

private void prepare3Ddrawing(GL10 gl)
{
    gl.glLoadIdentity();
    gl.glViewport(0, 0, getWidth(), getHeight());
    gl.glDisable(GL10.GL_DITHER);
    gl.glEnable(GL10.GL_DEPTH_TEST);
    gl.glEnable(GL10.GL_CULL_FACE);
    gl.glMatrixMode(GL10.GL_PROJECTION);
    gl.glLoadIdentity();
    GLU.gluPerspective(gl, 45.0f, (float)getWidth()/(float)getHeight(),0.1f,100.0f);    
}
private void prepare2Ddrawing(GL10 gl)
{
    gl.glDisable(GL10.GL_CULL_FACE);
    gl.glDisable(GL10.GL_DEPTH_TEST);
    gl.glMatrixMode(GL10.GL_PROJECTION);
    gl.glLoadIdentity();
    GLU.gluOrtho2D(gl,0,getWidth(), 0, getHeight());
    gl.glScalef(1, -1, 1);
    gl.glTranslatef(0, -getHeight(), 0);
    gl.glMatrixMode(GL10.GL_MODELVIEW);
}

And here is my draw method...

public void onDrawFrame(GL10 gl)
{
    gl.glClear(GL10.GL_DEPTH_BUFFER_BIT|GL10.GL_COLOR_BUFFER_BIT);  
    prepare3Ddrawing(gl);

    camera.draw(gl);
    go2d.draw(gl);

    prepare2Ddrawing(gl);
    go2d.draw(gl);

}

and finally, my go2d object is an instance of an object I created called GameObject2d. It's draw method looks like this...

@Override
public void draw(GL10 gl)
{
    super.draw(gl);

    gl.glEnable(GL10.GL_TEXTURE_2D);
    gl.glEnable(GL10.GL_ALPHA_TEST);
    gl.glAlphaFunc(GL10.GL_GREATER, 0.0f);
    gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
    gl.glTexCoordPointer(2,GL10.GL_FLOAT,0,textureBuffer);
    gl.glBindTexture(GL10.GL_TEXTURE_2D, textureID);

    gl.glBlendFunc(GL10.GL_SRC_ALPHA, GL10.GL_ONE_MINUS_SRC_ALPHA);
    gl.glEnable(GL10.GL_BLEND);


    gl.glFrontFace(GL10.GL_CW);
    //gl.glEnable(GL10.GL_CULL_FACE);
    gl.glCullFace(GL10.GL_BACK);
    gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
    gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuffer);

    gl.glDrawElements(GL10.GL_TRIANGLES, 6, GL10.GL_UNSIGNED_SHORT, indexBuffer);
    gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
    gl.glDisableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
    gl.glDisable(GL10.GL_CULL_FACE);
    gl.glDisable(GL10.GL_ALPHA_TEST);
    gl.glDisable(GL10.GL_TEXTURE_2D);   
}

Does anyone have any ideas? Again, I am still able to see the 3D rendered version of the go2D object, but I do not see the 2D version.

Thanks.

Answer 1

As you don't include any data, I can only propose two methods to debug the issue.

Step 1: try to force your 2d - perspective matrix and modelview matrix to be Identity Matrices. Then if you force your Square data vertices inside the clip space (eg x,y = +-1 or x,y= +-0.75, z=0, you should see a square appearing in the screen.

Step 2: now that the data model is correct, check what your model view and perspective matrices do: multiply each of your square vertices (x,y,z, w=1) with ModelView Matrix * CameraMatrix * PerspectiveMatrix. What do you get? Are the x,y,z much outside |w| ?