I managed to improve my xkbgrowl program a bit this week-end, the icon on the program sending the event is now converted to a growl icon within the program and not round-tripped via the file-system. Using the file-system has the advantage that I could use existing APIs: X11 knows how to export files in the x-bitmap format, a format that strangely enough, OS X still can read. Safari on OS X is one of the last browsers that supports that strange format (don’t bother checking for buffer overflows, I already did).

Doing the conversion explicitly in the program required some API archeology, I used XLib a bit when I was in the university, but I have largely forgotten what I did then, and I was mostly concerned in pushing pixels out, her the goal is to read some structures provided by the window manager.

I managed to get something that kind of works, which basically mimics the behaviour of XWriteBitmapFile, resolving the pixels using XGetPixel. This means I can get the same black/white images I already had, but instead of pushing to a file, I write the data into a buffer which I give the Core Image, which I used to scale the image and serialise it for Growl.

The frustrating part is that XGetPixel does not return information in RGB format, instead I get a reference in some colour table. From the documentation, I should call XQueryColor to resolve the colour into RGB, but when I do so, the whole program crashes with an illegal access. So I’m stuck with OK images for basic programs like xlogo and broken ones for things link xterm.

It is interesting to consider the two graphic APIs I’m trying to connect: their designs are a quarter century apart the first one handles colours as precious resources that are named and allocated and associated with a screen, you cannot simply work with an unattached image buffer. The other is all about buffers and transformations, memory is not the main constraint, but structuring the data-flow in a way that is understandable for the GPU is.

Anyhow, the new version is available in the releases section of github.