Load huge texture in parts in OpenGL ES 2.0

Question

I'd like to load a huge bitmap as a texture into the graphics card's memory on Android, in OpenGL ES 2.0, to be used as a texture atlas, in the biggest size possible. My device has a maximum texture size of 8192x8192.

I know that I can load a bitmap as a texture the following way:

// create bitmap
Bitmap bitmap = Bitmap.createBitmap(8192, 8192, Bitmap.Config.ARGB_8888);
{ // draw something
    Canvas c = new Canvas(bitmap);
    Paint p = new Paint(Paint.ANTI_ALIAS_FLAG);
    p.setColor(0xFFFF0000);
    c.drawCircle(4096, 4096, 4096, p);
}
// load as a texture
GLUtils.texImage2D(GL_TEXTURE_2D, 0, bitmap, 0);

However, (not surprisingly) I get a java.lang.OutOfMemoryError when trying to create a bitmap of this size.

Is it possible to load it in parts ? As it's a texture atlas, it could be assembled from smaller bitmaps. I looked at the texSubImage2D function, but I don't understand where you would initialize the full-sized texture, or provide the size of the full texture beforehand.

Answer 1

On the GL side you need to allocate the full storage, and then patch it.

Allocate storage using glTexImage2D() with a null value for the data parameter. Upload patches using glTexSubImage2D() .

Note that this still requires 256MB of memory, so on many budget devices you'll still get an OOM ...

Answer 2

Based on solidpixel's answer, this is a code that does the job:

GLES20.glTexImage2D ( GLES20.GL_TEXTURE_2D, 0, GLES20.GL_RGBA, 8192, 8192, 0,
        GLES20.GL_RGBA, GLES20.GL_UNSIGNED_BYTE, null);

Bitmap bitmap = Bitmap.createBitmap(1024, 1024, Bitmap.Config.ARGB_8888);
Canvas c = new Canvas(bitmap);
Paint p = new Paint(Paint.ANTI_ALIAS_FLAG);
for (int i = 0; i < 8; ++i) {
    for (int j = 0; j < 8; ++j) {
        // clear the bitmap
        c.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);
        { // draw something
            p.setARGB(255, 32 * i, 32 * j, 255 - 32 * j);
            c.drawCircle(512, 512, 512, p);
        }
        // load as part of a texture
        GLUtils.texSubImage2D(GL_TEXTURE_2D, 0, i * 1024, j * 1024, bitmap);
    }
}

Here the texture is assembled from 64, 1024x1024-sized bitmaps.