RE: Re: [gl4java-usergroup] glDrawElements

[<pet...@ba...>]

Must be me then...just thought I'd try and eliminate that option before 
I spent too much time looking into it... Thanks.


> -----Original Message-----
> From: kbr...@al... [mailto:kbr...@al...]
> Sent: Tuesday, November 27, 2001 6:35 AM
> To: pet...@ba...
> Cc: gl4...@li...
> Subject: Re: [gl4java-usergroup] glDrawElements
> 
> 
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> 
> 
> > Java doesn't have any unsigned data types, so this method 
> dies a death 
> > when the signed data is read as unsigned, it becomes 
> massive and the 
> > native code tries to read beyond the end of the array.
> > 
> > Or at least thats what I think is happening. I can't find 
> any examples 
> > in the demos that use glDrawElements: is this because it 
> doesn't work?
> 
> http://java.sun.com/products/jfc/tsc/articles/jcanyon/
> 
> See the source code, specifically terrain.MultiResTile.
> 
> Signed versus unsigned only really becomes an issue when
> promoting to a larger type; for example, byte to int. If the high
> bit is set and the type is signed (as all types are in Java) then
> the value will be sign-extended. In Java this is most problematic
> when dealing with byte and short types which automatically get
> promoted to ints in intermediate expressions. I frequently
> promote to int early, masking appropriately if necessary, and
> deal with ints from then on.
> 
> However, when dealing with OpenGL, one can pretty much ignore the
> issue. You need to ensure that you are using the correct Java
> data type to match the one expected by OpenGL (byte for
> GL_UNSIGNED_BYTE, short for GL_UNSIGNED_SHORT, and int for
> GL_UNSIGNED_INT). Even if the values in the array overflow into
> the high bit (and therefore become negative in Java's view),
> OpenGL will treat them properly.
> 




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