[Qt4-preview-feedback] Bad drawing speed under OSX

[Trenton Schulz]

On 2009-02-09 11:46:41 +0100, Gunnar Sletta <gunnar at trolltech.com> said:

> Philippe wrote:
>> Running my application under OSX Leopard and Windows XP, using 
>> bootcamp,  hence with the same hardware, I have always noticed that 
>> running under  Windows seems much faster. For instance run Assistant 
>> and scroll and  resize the window, it's quite a different feeling.
>> I have therefore run a very simplistic benchmark, see further.
>> Using the 4.5 rc1 32 bit supplied binaries, the results are (Mac Pro 
>> 2.8  GHz), in RELEASE mode:
>> 
>> Under Windows:
>> With QImage as paint device: 78 ms
>> With direct QPainter device: 78 ms
>> 
>> Under OSX:
>> With QImage as paint device: 98 ms
>> With direct QPainter device: 562 ms
>> 
>> Hence:
>> 
>> 1) Drawing to a QImage is meant to be platform independant,
>> this means here that the VC++ 2008 compiler seems about 20% faster that  GCC.
>> I am wondering if using an alternate GCC version could help (LLVM-GCC 4.2  ?)
> 
> This doesn't surprise the least. Visual Studio rocks when it comes to 
> optimzing code ;)

That's not to say that another compiler couldn't help. Be aware that 
the version of llvm-gcc that's included with the current developer 
tools has some issues compiling Qt (especially at -O4) (and we aren't 
actively testing that configuration at the moment).

-- Trenton