The latest alpha build of Paint.NET v3.5 will now use DirectWrite instead of GDI for the Text tool if you are running Windows 7. Get it while it’s hot: http://paintdotnet.forumer.com/viewtopic.php?f=46&t=31132

DirectWrite is a new font and text rendering system that comes with Windows 7. In Paint.NET, you’ll see the following benefits:

  • Faster text rendering. This is currently due to important architectural differences from GDI. With DirectWrite, I can render using multiple threads (performance scaling), while also not blocking the UI thread from drawing (mutexing). GDI can only render text on 1 thread at a time, and that also includes the thread responsible for the UI. DirectWrite can also benefit from GPU acceleration when things are set up correctly with Direct2D (Paint.NET only uses the software rasterization capabilities right now, but in the future who knows!).
  • Better quality text rendering. DirectWrite implements what is called “y-direction antialiasing”. The short story is that GDI apparently only does antialiasing on the horizontal axis. It can also position characters with sub-pixel accuracy … in other words, GDI uses integers and DirectWrite uses floating point.

When it comes to performance you can see the difference just by opening Paint.NET, switching to the Text tool, and clicking on the font list dropdown. In GDI you’ll see the font previews slowly trickle into view, and scrolling can get laggy and “stalled” (the difference is very pronounced if you have lots of fonts installed – I have over 2000 on my system). With DirectWrite it’s nearly instantaneous and also very zippy when scrolling. If you type many lines of text onto the canvas, Paint.NET will use up to 1 thread per line for rendering (capped by the number of cores your CPU has), and on a dual- or quad-core system the performance benefit can add up. Systems with more cores/threads/CPUs will see the most benefit for both scenarios (yes, HyperThreading helps).

I tested on a 3.6GHz Core i7 and a 1.6GHz Atom. On both systems, DirectWrite was a big performance improvement.

Also, you can turn off DirectWrite in Paint.NET by launching the program with the /disableDirectWrite command-line parameter. This is quite useful for comparing the two renderers. If you don’t know what a “command-line parameter” is, then don’t worry about it :)

Thanks go out to Dwanye Robinson (at Microsoft) for helping out.

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