On Thu, Jul 5, 2012 at 12:39 PM, Christoph Feck <christ...@maxiom.de> wrote:
> 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... > Thanks, Christoph - that is an amazing trick! I just read the article with my jaw dropped - nicely done! Even though I don't think this will work for my particular application, I'll definitely tuck this little nugget of code away in my list of "gems" to use later. Thanks again! -- Josiah Bryan 765-215-0511 josiahbr...@gmail.com
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