[OpenGL] When textures do not show properly without any glerror in Android

While I was exploring the features of Rajawali creating some sample code, I have encountered into a strange situation where textures show up on one device and another didn't. Nothing complicated in the sample code going on. Just rendering a sphere object with a texture of the earth's surface. The image used for the texture was saved in res/drawable and the bitmap was created at runtime using BitmapFactory.decodeResource(). Now the most strange thing was that glError was not flagged at any point(at least I think I checked thoroughly).

FYI, the working devices was Galaxy Nexus, and the non-working device was Galaxy Player GB70

To attack this issue, I've created a simple project which renders a flat square with the image that I'm having trouble to use it as the sphere's texture in Rajawali.

The first thing I noticed was that the only difference between the working device and the non-working device was that the image was decoded into a ARGB8888 bitmap config on the working device and RGB565 bitmap config on the non working device. However, if I force the image to be decoded into RGB565 bitmap config on the working device, it still worked.

I've tried changing parameters for glTexImage2D and converting the image file to use another bitmap config(via Bitmap.copy()) and all sorts of things without much luck. So I did more Googling to do more research.

There is probably almost any information you want on the Internet. And I have found the reason why the texture was not showing properly. A piece of meaningful information here. The person who was having a similar problem that I was having posted a question on stackoverflow. Luckily he found the solution on his own and was nice enough to share the information he learned. Special thanks to him/her.

In Android, image resources could be packaged in path res/drawable. Since there exists many Android devices with different screen resolution the image resources are designed to be packaged in various size in drawable-ldpi, drawable-mdpi, drawable-hdpi under res/. And for the sake of convenience you can package resources under simply res/drawable and then the system would automatically handle the resizing. Here's a quote from the Android developer's page regarding supporting multiple screen resolutions.

The "default" resources are those that are not tagged with a configuration qualifier. For example, the resources in drawable/ are the default drawable resources. The system assumes that default resources are designed for the baseline screen size and density, which is a normal screen size and a medium density. As such, the system scales default density resources up for high-density screens and down for low-density screens, as appropriate.

http://developer.android.com/guide/practices/screens_support.html

This is something that I wasn't completely unaware of, but it bit me. The problem might have been when the resource was decoded into a bitmap using the BitmapFactory, the size of the image changes into probably something not in the dimensions of power of two. The OpenGL ES 2.0 specification indicates that it supports non-power of two textures. See the OpenGL ES 2.0 common profile specification  p. 17 on section 3.8 Texturing. However, for some reason I'm suspicious about every OpenGL ES 2.0 implementation strictly following this specification. 

What I didn't really know was that drawable resources under res/drawable-nodpi is dpi independent resource which the system does not perform any resizing when decoded into bitmap. Honestly, I thought drawable resources under res/drawable would be decoded in a dpi independent manner too.

 

I'll have to see if the problem was caused by resizing the resource into a non-power of two dimension. If this were true I'm also surprised that glError was not flagged at all. Anyway, but for now, if you are having trouble loading textures in Android check if your drawable resource that you are using as your texture is packaged under res/drawable.

Problem partly solved, but still the texture is not showing up for some cases on the sphere when using Rajawali. so the research goes on...

If you have any knowledge about this problem or if I have written something incorrect here please leave a comment and let me know.