tiny mistake in an example using LWJGL on nehe.gamedev.net

OpenGL Development
#1

Hi

I’m sorry to disturb you with this, the email address of the author of this port is no more valid. You can find the example here:
http://nehe.gamedev.net/data/lessons/lwjgl/lesson32.jar

The depth values in the select buffer are unsigned 32-bits integer and are stored into signed 32-bits integer. Of course, when the depth is greater than 2^31, the source code stores a negative value.

The actual code is:

temp = ByteBuffer.allocateDirect(2048).asIntBuffer();
GL11.glSelectBuffer(temp);                                // Tell OpenGL To Use Our Array For Selection
temp.get(buffer);

hits = GL11.glRenderMode(GL11.GL_RENDER);                               // Switch To Render Mode, Find Out How Many
// Objects Were Drawn Where The Mouse Was
if(hits > 0) {                                               // If There Were More Than 0 Hits
     int choose = buffer[3];                                 // Make Our Selection The First Object
     int depth = buffer[1];

The last line should be modified:

long depth = buffer[1] & 0xffffffffL;

Best regards.

#2

That buffer allocation should also include an order call, like so:

temp = ByteBuffer.allocateDirect(2048).order(ByteOrder.nativeOrder()).asIntBuffer();

Anyway, I can’t see how that code could work, since it’s doing a temp.get(buffer) immediately after glSelectBuffer and before rendering anything. Or am I missing something?

#3

the official nehe site LWJGL source code (AFAIK) has not been updated in a while.

I submitted a fix to lesson27 stencil shadows ages ago. and it never got updated.

#4

This source code seems outdated and may contain other errors. If I had some time, I would have a deeper look at this example. I only noticed the common errors that I fixed several times somewhere else.

Maybe updating all lessons and putting the source code directly somewhere onto the official website of LWJGL would be better.

#5

if you need a better lwjgl source code port of the nehe tutorials you can find them here. The source there is much nicer and better looking.

#6

unfortunately I can’t start the webstart examples from the site, as the lwjgl-1.1.4-extension.jnlp doesn’t specify lwjgl natives for linux x86_64.

#7

You’re right but there are only 25 lessons, lots of lessons are missing. Thank you for the pointer.

You’re right. It works with 32 bits linux but when I leave the application, the process is still up.