Switched byte order in result of glGetActiveAttrib in LWJGL

Question

I tried to compare output of glGetActiveAttrib (values type & size) against OpenGL constants and didn't get reasonable results. After some experiments I noticed that the byte order is switched, so this code:

    ByteBuffer auxType = ByteBuffer.allocateDirect(4);
    IntBuffer type = auxType.asIntBuffer();
    ByteBuffer auxSize = ByteBuffer.allocateDirect(4);
    IntBuffer size = auxSize.asIntBuffer();
    String name = glGetActiveAttrib(shader.program, 1, size, type);
    System.out.println(type.get(0));

outputs 1384841216. After re-ordering bytes I get 35666 (GL_FLOAT_VEC4) - that is correct. Same problem with size value. Is there any little-big endian switch in LWJGL or could it be issue with graphic card driver? I'm using LWJGL 3.1.1, graphics card is NVIDIA GTX 1060.

Answer 1

Is there any little-big endian switch in LWJGL or could it be issue with graphic card driver?

It's actually all about the ByteBuffer itself. It has a byte order. So instead of creating the type ByteBuffer like this:

IntBuffer type = ByteBuffer.allocateDirect(4)
                           .asIntBuffer();

You create it and tell it the byte order:

IntBuffer type = ByteBuffer.allocateDirect(Integer.BYTES)
                           .order(ByteOrder.nativeOrder())
                           .asIntBuffer();

Also since you're using LWJGL, you can also use the static helper class org.lwjgl.BufferUtils and instead just do:

IntBuffer type = BufferUtils.createIntBuffer(1);

Now type.get(0) should correctly yield 35666 instead of 1384841216. If you apply the same to size, then that should equally yield the assumed value.

Since you didn't supply a shader, I tested it with:

...
layout(location = 1) in vec3 position;
...

Then when calling glGetActiveAttrib it correctly yielded:

String name = glGetActiveAttrib(shader.program, 1, size, type);
System.out.println(name); // prints "position"
System.out.println(type.get(0)); // prints "35665"
System.out.println(size.get(0)); // prints "1"

Remember that size is just the element count of the array, so since we aren't dealing with an array it yields 1.