OpenGL: C and D same code - different results

[Dave]

The depth and breadth of experience and knowledge in this NG continues to amaze me...

Bill Baxter wrote:
> dyh wrote:
>> recently I've tried few OpenGL examples ported from C to D (on win32)
>> and have run into strange problems.
>>
>> Translated example was built against same C libs as original, using same
>> (translated from platform sdk) headers. Resulted binary is using same 
>> dlls
>> as original. But there are some differences:
>>
>> 1. Behavior
>> In original calls glIndexi() has *no* effect. In translation has.
>> In original calls glColor3f() has effect. In translation has *not*.
>> In original initial color is white. In translation it is kind of brown.
>>
>> 2. Performance
>> original example performs noticeably faster than translated one.
>>
>> No matter what compiler switches I've tried (-O, -inline, -release, etc).
>> Example is extremely simple, and i do not see any possibilities to 
>> have any
>> difference in performance. There is no GC used - there are no memory
>> allocations array slice at all. Actually there are no array usage. In 
>> fact
>> there is nothing at all except opengl api calls. And it is literally same
>> library in both example and translation.
>>
>> Here is code (~300 lines) original (C) 
>> http://paste.dprogramming.com/dpfwrsgw.php
>> translation (D) http://paste.dprogramming.com/dpu768pr.php.
>>
>> Any tips from opengl experts?
> 
> I don't know why, but it seems pretty clear from the results you're 
> seeing that the original version didn't actually get the 
> PFD_TYPE_COLORINDEX visual it was asking for, whereas the D version 
> does.  That would explain the performance difference too because a color 
> index visual is probably going to be slow on most modern hardware.
> 
> Recent hardware may not even support color index buffers, so it may mean 
> you're getting a fallback software renderer in the D case.
> 
> Is there some reason why you really need to use a color index visual? 
> You'd be much better off with a true color visual.
> 
> --bb