[android-developers] Re: Drawing 2D stuff on the screen in OpenGL over a 3D scene

Many many many thanks. I'll get back to you whether it works or not. I
was still in projection matrix mode (and not modelview) before drawing
the 2D stuff (from the OpenGL FAQ for drawing 2D controls). I'll tell
you whether modelview works or not. Nightwolf - thanks, yeah I forgot
to mention I did try that.

On Jun 28, 5:10 pm, Robert Green <rbgrn....@gmail.com> wrote:
> Here's the standard method for a 3D game w/2D controls:
>
> onSurfaceChanged:
> this means you have a new GL context so it's a fresh state machine
> ready to be configured.
> set viewport and enable and configure things that will always be used,
> like texturing, texture coordinate arrays, vert arrays, erase color,
> etc
> you can set your projection matrix here if it's going to be fixed
> load textures, vbos and anything else into vram
>
> onDrawFrame:
> clear depth and color buffer
> for dynamic projection (like if FoV or near/far clip plane can
> change), switch to projection matrix, load identity and set.
> switch to modelview matrix
> set lookAt
> enable depth test
> // draw each totally opaque object sorted front to back
> for (GameObject gameObject : sortedGameObjects) {
>   push matrix
>   draw opaque parts of the object
>   pop matrix}
>
> // draw alpha blended parts of objects sorts back to front
> enable blending
> for (GameObject gameObject : sortedGameObjects) {
>   push matrix
>   draw alpha parts of the object
>   pop matrix}
>
> // draw HUD
> switch to projection matrix
> push matrix
> set ortho
> switch to modelview matrix
> push matrix
> load identity
> disable depth test
> // draw HUD components in orthographic screen space
> enable depth test
> pop matrix
> switch to projection matrix
> pop matrix
> // done - the way the matrix stack was handled here means the
> projection and modelview are exactly as they were before the HUD was
> drawn, so for the next frame, your projection doesn't need to be reset
> unless it's dynamic (changing fov or near/far clip)
>
> On Jun 27, 7:01 am, Navigateur <naveen.c...@googlemail.com> wrote:
>
> > Can somebody take me step-by-step how to draw 2D stuff over a 3D scene
> > (such as controls, etc.). What I've been doing so far has not been
> > working (it only draws the 3D scene), which is (in every frame): draw
> > the 3D scene as normal, projection matrix mode, load identity, call
> > GLU.gluOrtho2D(gl, 0, myScreenWidthInPixels, 0,
> > myScreenHeightInPixels), switch the array pointers (vertices and
> > texture coords) to the ones for my 2D stuff, then drawElements with an
> > appropriate index list. (then switch the array pointers back so the 3D
> > stuff works again).
>
> > I get nothing added to the screen (just the 3D stuff).
>
> > Do I need to be doing something else for it to draw? Can somebody take
> > me step-by-step?
>
>

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