问题
I found a 3D graphics framework for Android called Rajawali and I am learning how to use it. I followed the most basic tutorial which is rendering a shpere object with a 1024x512 size jpg image for the texture. It worked fine on Galaxy Nexus, but it didn't work on the Galaxy Player GB70.
When I say it didn't work, I mean that the object appears but the texture is not rendered. Eventually, I changed some parameters that I use for the Rajawali framework when creating textures and got it to work. Here is what I found out.
The cause was coming from where the GL_TEXTURE_MIN_FILTER was being set. Among the following four values
GLES20.GL_LINEAR_MIPMAP_LINEAR
GLES20.GL_NEAREST_MIPMAP_NEAREST
GLES20.GL_LINEAR
GLES20.GL_NEAREST
the texture is only rendered when GL_TEXTURE_MIN_FILTER is not set to a filter using mipmap. So when GL_TEXTURE_MIN_FILTER is set to the last two it works.
Now here is the what I don't understand and am curious about. When I shrink the image which I'm using as the texture to size 512x512 the GL_TEXTURE_MIN_FILTER settings does not matter. All four settings of the min filter works.
So my question is, is there a requirement for the dimensions of the image when using min filter for the texture? Such as am I required to use an image that is square? Can other things such as the wrap style or the the configuration of the mag filter be a problem?
Or does it seem like a OpenGL implementation bug of the device?
回答1:
Good morning, this a typical example of non-power of 2 textures.
Textures need to be power of 2 in their resolution for a multitude of reasons, this is a very common mistake and it did happen to everybody to fall in this pitfall :) too me too.
The fact that non power of 2 textures work smoothly on some devices/GPU, depends merely to the OpenGL drivers implementation, some GPUs support them clearly, some others don't, I strongly suggest you to go for pow2 textures in order to be able to guarantee the functioning on all the devices.
Last but not least, using non power of 2 textures can lead you to a cathastrophic scenarious in GPU memory utilization since, most of the drivers which accept non-powerof2 textures, need to rescale in memory the textures to the nearest higher power of 2 factor. For instance, having a texture of 520X520 could lead to an actual memory mapping of 1024X1024.
This is something you don't want because in real world "size matters", especially on mobile devices.
You can find a quite good explanation in the OpenGL Gold Book, the OpenGL ES 2.0:
In OpenGL ES 2.0, textures can have non-power-of-two (npot) dimensions. In other words, the width and height do not need to be a power of two. However, OpenGL ES 2.0 does have a restriction on the wrap modes that can be used if the texture dimensions are not power of two. That is, for npot textures, the wrap mode can only be GL_CLAMP_TO_EDGE and the minifica- tion filter can only be GL_NEAREST or GL_LINEAR (in other words, not mip- mapped). The extension GL_OES_texture_npot relaxes these restrictions and allows wrap modes of GL_REPEAT and GL_MIRRORED_REPEAT and also allows npot textures to be mipmapped with the full set of minification filters.
I suggest you to evaluate this book since it does a quite decent coverage to this topic.
来源：https://stackoverflow.com/questions/11427010/opengl-es-2-0-texture-not-showing-on-some-device