[Interest] Filling a 3-Color Triangle - A Better Way?

[Christoph Feck]

On Thursday 05 July 2012 17:12:04 Josiah Bryan wrote:
> Hello, All!
> 
> I have a particular need to fill a triangle (heck, I'll take a poly
> if I could get it, but triangles are simpler to code) with a
> different color at each vertex. However, since I can't use OpenGL
> on my target device, I must use vanilla Qt.  After much googling,
> I found a routine in delphi (
> http://www.swissdelphicenter.ch/en/showcode.php?id=1780) that I
> translated to Qt/C++ (see attached file - MainWindow.cpp - should
> compile and run just fine as is, just throw in a folder, qmake
> -project && qmake && make then run it.)
> 
> A sample of what the rendered triangle looks like is also attached
> - "sample.jpg"
> 
> The new routine, fillTriColor(), works fine quality-wise - but
> performance is abysmal at best - almost 4 sec for 1K triangles on
> a dual-core 3 GHz processor! Crikey.  I also tried adapting the
> routine to use a QLinearGradient to fill each scanline (instead of
> iterating over each column and filling the pixels directly - code
> is present in MainWindowp.cpp but commented out) - but that
> ballooned the time it took for 1K triangles to almost *7 seconds*
> - crikey!
> 
> So, my Qt friends, is there a better way to fill a triangle with a
> color specified for each vertex, interpolated across the triangle?
> Some method that takes *less* than 4 milliseconds *per triangle*?
> Did I just miss something in the Qt gradient routines that would
> do this quite easily? Any ideas?
> 
> Thanks so much!
> -Josiah

Here http://paste.kde.org/513062/ is some example code to fill a four-
corner gradient quad, based on the idea described here 
http://kdepepo.wordpress.com/2010/05/03/accelerating-color-gradients/

Unfortunately, due to the perspective transform it won't work for 
triangles...

-- 
Christoph Feck
http://kdepepo.wordpress.com/
KDE Quality Team