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So, I'm trying to figure out LWJGL, and my goal is to use OpenGL 3.2 (because pretty shaders are pretty). But in every tutorial I can find for LWJGL, they import a bunch of different OpenGL versions and use them at the same time. For example, this one imports GL11, GL15, GL20, and GL30 and uses functions from all of them. This seems intuitively like it would be messy and generally a bad idea. Besides the normal disadvantages of using deprecated functions, is there any particular reason not to do this? Could it affect performance in any way? Is there a potential for errors and odd behavior to occur?

Also, if possible, does anyone have an example of LWJGL written only using GL32? I've found C++ code samples that do this, but I'm not too familiar with C++, so it's difficult for me to translate.

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2 Answers

LWJGL prefaces all core functions and enumerators with the OpenGL version that those functions were introduced in. So glBindBuffer, a function introduced in OpenGL version 1.5, is called GL15.glBindBuffer.

That's just how it works. It's not really importing "a bunch of different OpenGL versions"; it's just using the version those functions/enumerators was introduced in as a "namespace" scope.

That way, if you're writing to a specific OpenGL version, it's easier to prevent yourself from using functions that aren't available in that version. Of course, OpenGL core extensions kinda confound this notion.

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As Nicol Bolas said, the version number corresponds directly to the version number were a symbol, function or constant was introduced.

It's probably impossible to write a working application using only the GL32, or any one namespace for that matter (maybe apart from GL11). For instance look at this snippet from my game:

    this.fbo = GL30.glGenFramebuffers();
    GL30.glBindFramebuffer(GL30.GL_FRAMEBUFFER, fbo);

    GL30.glFramebufferTexture2D(GL30.GL_FRAMEBUFFER, GL30.GL_COLOR_ATTACHMENT0, GL11.GL_TEXTURE_2D, this.fboImg, 0);
    GL30.glFramebufferTexture2D(GL30.GL_FRAMEBUFFER, GL30.GL_COLOR_ATTACHMENT1, GL11.GL_TEXTURE_2D, this.fboTileCoordsImg, 0);
    GL30.glFramebufferTexture2D(GL30.GL_FRAMEBUFFER, GL30.GL_DEPTH_ATTACHMENT, GL11.GL_TEXTURE_2D, this.depthImg, 0);

    int status = GL30.glCheckFramebufferStatus(GL30.GL_FRAMEBUFFER);
    if (status != GL30.GL_FRAMEBUFFER_COMPLETE)
    {
        throw new RuntimeException("Framebuffer creation failed with code: " + status);
    }

    IntBuffer scratchBuffer = BufferUtils.createIntBuffer(2);
    scratchBuffer.put(0, GL30.GL_COLOR_ATTACHMENT0);
    scratchBuffer.put(1, GL30.GL_COLOR_ATTACHMENT1);
    GL20.glDrawBuffers(scratchBuffer);

I'm using glFramebufferTexture2D which came with OpenGL30, but I need the constant GL11.GL_TEXTURE_2D. Later on I need to call glDrawBuffers which comes from GL20. Nothing fishy here; I just an older function to do a newer thing, like the OpenGL docs tell me to. Besides, I don't really have a choice :)

What you should worry about are deprecated functions, like these: glBegin, glEnd, glVertex*, glNormal*, glTextCoord*, glTranslate*, glRotate*, glScale*, glLoadIdenity, glModelViewMatrix... etc. Generally everything that uses fixed pipeline or the matrix stack.

If you are worried if you are using deprecated functionality, you can force LWJGL to create a strictly core profile rendering context with an appropriate openGL version by passing an appropriate ContextAttribs to Display.create.

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