How to save large texture (efficiently) by OpenGL ES 2.0 in Android

Question

Now, I can save texture by using glReadPixels() to read the data in framebuffer (FBO). However, I faced two problems.

(1) In order to keep the saved image quality, the dimension would be larger than GL_MAX_TEXTURE_SIZE (most devices is 4096). If I created big texture (ex: 4160x3120), I got GL_FRAMEBUFFER_UNSUPPORTED error when calling glCheckFramebufferStatus()....

(2) If I created small texture(ex: 3648x2736), everything works except glReadPixels() will be very slow....

So back to my question, is it possible to overcome max texture size limitation and save it efficiently? Thanks.

Answer 1

1) No, it's not possible unless you want to somehow process the image in multiple, smaller pieces. I don't remember seeing a device with bigger GL_MAX_TEXTURE_SIZE than that, so you won't be able to create a FBO bigger than that.

EDIT: Actually, there is quite a number of devices where the maximum texture size is 2048, although 4096 is typical in most recent devices.

2) You should understand that that is already a very large texture, not a small one, so glReadPixels() will be slow. I'm not sure there's a way around this on Android.