What's the difference between GL_TEXTURE_2D and GL_TEXTURE_EXTERNAL_OES

Question

I'm new to OpenGL ES in android development. I found two types of texture during my study:

1. GL_TEXTURE_2D
2. GL_TEXTURE_EXTERNAL_OES

I was told that they are not compatible with each other.

I have two questions:

1. What's the difference between them? Are they completely different types of textures?
2. Does GL_TEXTURE_EXTERNAL_OES texture has to be YUV format? If not, what decides the data format?

Answer 1

What's the difference between them?

Normal textures are defined, allocated, and managed entirely by OpenGL ES.

External textures are defined and allocated elsewhere, and imported into OpenGL ES in some implementation-defined manner. One common use is for importing YUV video, so external samplers also have to be able to handle color-space conversion and non-standard memory layouts (e.g. multi-plane YUV surfaces).

Does GL_TEXTURE_EXTERNAL_OES texture has to be YUV format?

No. Some external entity in the system defines the format - it's invisible to the application, and color space conversion is magically handled by the driver stack. Exactly what formats are supported is implementation-defined.