I'm sure this has been asked a thousand times, even though I have yet to find the answer, but I have searched for a week now and I just can't get the hang of it. I'm trying to draw a bitmap(in 2d space directly to the screen) over an opengl 3d scene. From what I understand you have to load the bitmap as a texture and then there's a lot of stuff about matrices that I don't understand. The main question I have is why is there not a simple way like canvas.drawBitmap(bitmap, x, y) instead of all that other stuff, I honestly don't see the point. Mostly I get frustrated because I don't understand matrices, is there anywhere a description for someone that's a little slow to learn this thing? Please can someone give me a simple example, like a cube in 3d space, and then arrows in 2d space that control rotation of the cube? Just basically how to draw bitmaps over a 3d scene.

There is, I've been struggling on this for the last few days, use

((GL11Ext) gl).glDrawTexfOES

That function draws a 2d texture directly to the screen... You've also got to crop the texture before drawing it as well but I don't have access to source code at the moment. Have a look at replicaisland source code, everything in there is drawn using glDrawTexfOES. Theres barely any documentation on the web about it.

Yes, glDrawTex is the easiest, so long as it's supported by the device. It's not guaranteed. The next way is to, after having drawn your entire 3D scene, is to clear the Z buffer, set up an orthogonal projection, then render textured quads to the screen. This is, IMO the /better/ way to do it because glDrawTex* does not support rotation of textures, only scaling. Building your 2D functionality in using geometry instead of direct texture rendering will be more flexible. The problem is that in Android pushing vertices is far slower than glDrawTex. This could be due to an known bug in Android's implementation of FloatBuffer, but since this bug lives on hundreds of thousands of phones that are already out there and not going away any time soon, you haven't much of a choice but to work around it.

And yes, you'll have to set up the texture crop parameters before you call glDrawTex.

The relevant code for rendering a quad with glDrawTex:

Code: Select all

gl.glBindTexture(GL10.GL_TEXTURE_2D, textureId);
int[] crop = new int[] {
    sourceTextureX, sourceTextureY,  // Coordinates to use from the SOURCE texture. NOT where it will be drawn to the screen
    sourceTextureWidth, -sourceTextureHeight  // use a negative height to flip the image upside down
}

gl.glEnable(GL10.GL_TEXTURE_2D);
((GL11) gl).glTexParameteriv(GL10.GL_TEXTURE_2D, GL11Ext.GL_TEXTURE_CROP_RECT_OES, crop, 0);
((GL11) gl).glDrawTexiOES(destinationX, destinationY, destinationZ /* typically 0 */, sourceTextureWidth, sourceTextureHeight);


Thanks guys, although it doesn't work with a negative sourceTextureHeight. Had to use the posetive although then it got upsidedown of course...

randomcracker wrote:Thanks guys, although it doesn't work with a negative sourceTextureHeight. Had to use the posetive although then it got upsidedown of course...

That's why you supply the negative source texture height. It flips the image. Try drawing at destinationY + height and see what happens when you supply negative sourceTextureHeight.

moblcade.com wrote:

randomcracker wrote:Thanks guys, although it doesn't work with a negative sourceTextureHeight. Had to use the posetive although then it got upsidedown of course...

That's why you supply the negative source texture height. It flips the image. Try drawing at destinationY + height and see what happens when you supply negative sourceTextureHeight.

Doesn't work, it doesn't draw it correctly.

randomcracker wrote:

moblcade.com wrote:

randomcracker wrote:Thanks guys, although it doesn't work with a negative sourceTextureHeight. Had to use the posetive although then it got upsidedown of course...

That's why you supply the negative source texture height. It flips the image. Try drawing at destinationY + height and see what happens when you supply negative sourceTextureHeight.

Doesn't work, it doesn't draw it correctly.

Strange... this code is copied from my working application.

Yeah no, I got it to work just now, changed the sourceTextureY to include height. Maybe that's what you ment? Anyhow GREAT! Finally an easy way to do this, thanks a lot!! Now I only have to get the 3d stuff to work. I'm trying to implement the modelloader.jar for android but I'm not having much luck with it. I can't understand why it works to draw a model in one place but as soon as I send the gl10 object to another class to draw using the exact same code it just doesn't draw anything. Wierd stuff this is.

randomcracker wrote:Yeah no, I got it to work just now, changed the sourceTextureY to include height. Maybe that's what you ment? Anyhow GREAT! Finally an easy way to do this, thanks a lot!! Now I only have to get the 3d stuff to work. I'm trying to implement the modelloader.jar for android but I'm not having much luck with it. I can't understand why it works to draw a model in one place but as soon as I send the gl10 object to another class to draw using the exact same code it just doesn't draw anything. Wierd stuff this is.

A lot of times it is because you haven't set up OpenGL properly. My issues usually are one of these:
* Forget to use a native buffer
* Forget to enable the correct gl state
* Incorrect modelview or projection matrix.
* Forget to check for GL errors when debugging.

Well, I don't see what can go wrong, I'm simply moving the code to a diffrent function in a diffrent class and calling it from where the code originally was.

Hi Guys,

This solution is great! But I need help.
I have used your code to draw 2D sprite over 3D and now it gets complicated:
on my Desire phone it looks great!
but Eclipse shows black square.

What I want to do is to create simple 2D animation - you may remember doom and guys face.. starts bleeding when life is below some value.. and now is my question:

is there any simple way of doing that so Eclipse will display that properly or do I have to check that on my phone?

Kind Regards,
Luke