Android OpenGL textures: creating and deleting them on the fly

Question

I am currently implementing a 3D viewer which basically renders a subset of all the images the user has on his SD Card. The closest matching product I would think of would be CoolIris:

It simply show a scrolling board of N tiles on screen, each showing different images, with new tiles entering the screen and showing new images.

Now for my problem: I have the program working and rendering nicely the quads. When a quad goes out of the screen, it gets recycled/released. And new quads keep on being added to the tile board before they enter the screen.

Because there can be hundreds of images, the textures need to be created and deleted on the fly (so that we don't run out of memory). The problem I have is that after I delete textures, newly created textures seem to get some IDs of other textures currently in use.

My rendering loop looks like this:

void render(GL10 gl) {
  0. Move the camera

  // Tile board maintenance
  1. Remove tiles out of screen
  2. Add new tiles which are about to enter screen

  // Texture handling
  3. glDeleteTextures on all unused textures followed by glFlush
  4. For newly used images
     - Create corresponding Bitmap
     - Create the OpenGL texture, followed by glFlush
     - Release the Bitmap

  // Rendering
  5. Render the tile (using a textured quad)

}

To give a better idea of how the data is organised, here is an overview of the classes:

TileBoard {
  Image[] allImages;
  Tile[] board;
}

Tile {
  Image image;
}

Image {
  String path;
  int textureId;
  int referenceCount;
}

Texture creation code:

protected void loadSingleTexture(GL10 gl, long objectId, Bitmap bmp) {
    int[] textures = new int[1];
    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_LINEAR);
    gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MAG_FILTER, GL10.GL_LINEAR);
    GLUtils.texImage2D(GL10.GL_TEXTURE_2D, 0, bmp, 0);
    gl.glFlush();

    if (bmp != null) bmp.recycle();

    if (listener != null) listener.onTextureLoaded(gl, objectId, textures[0]);
}

Texture deletion code:

// pendingTextureUnloads is a Set<Integer>
if (pendingTextureUnloads.size() > 0) {
  int[] textureIds = new int[pendingTextureUnloads.size()];
  int i = 0;
  Iterator<Integer> it = pendingTextureUnloads.iterator();
  while (it.hasNext()) {
    textureIds[i] = it.next();
  }

  gl.glDeleteTextures(textureIds.length, textureIds, 0);
  gl.glFlush();
}

Answer 1

I have solved the problem: the issue was that you have to keep the texture array passed to glGenTextures and reuse it.

Here is the modified overview for the ones who will have the same problem:

Image {
  String path;
  int[] textureIds;
  int referenceCount;
}

Texture creation code:

// Notice that I don't allocate the int[] at the beginning but use the one of the image
protected void loadSingleTexture(GL10 gl, Image img, Bitmap bmp) {
    gl.glGenTextures(1, img.textureIds, 0);
    gl.glBindTexture(GL10.GL_TEXTURE_2D, img.textureIds[0]);
    gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MIN_FILTER, GL10.GL_LINEAR);
    gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MAG_FILTER, GL10.GL_LINEAR);
    GLUtils.texImage2D(GL10.GL_TEXTURE_2D, 0, bmp, 0);
    gl.glFlush();

    if (bmp != null) bmp.recycle();
}

Texture deletion code:

foreach Image img {
  gl.glDeleteTextures(img.textureIds.length, img.textureIds, 0);
}
gl.glFlush();