Understanding the GNU/Linux graphics
Sometime ago, after reading some LWN articles (highly recomment an LWN subscription if you are interested in Linux kernel). But I found the going tough. There are lots of scattered information. Even though the software is all Free, it was impossible to comprehend why certain things were done the way it was done. It not only required reading articles (paying close attention to the date on which it was written), it also required digging into the past on how things looked before and how it changed. Most of the time, a long list of APIs are given which can only be comprehended by those working on it for a long time. It was very frustrating. I even wondered how anyone new can contribute to such projects after a few years when the current crop of experts have all lost interest in these projects or have passed away.
If you find yourself also in the same position as me, here are some pointers to some gems I found in my journey that does give a big picture of the GNU/Linux graphics/display sub-system. No, I am not competent enough to explain it myself yet, I would rather leave that to masters who have actually worked on it.
To get an overview of the various terminologies involved (DRM, DRI2, KMS, EGL, X, XRender, Wayland, pixman, cairo and other alphabet soup) start reading this overview article ”The Linux Graphics Stack”. Another great overview is this little PDF file which has short explanations of all the key pieces of the graphics stack from the hardware bits to the application. Once you read it, head straight to Wayland Architecture page which explains how X draws the screen and how Wayland is simplifying the picture. Pay particular attention to the journey of an event and its effect on the screen.
Another great video is the Episode 6 of “The luminosity of Free Software”, a Google Hangout series by KDE uberhacker Aaron Seigo. Another great article written in 2005 about the state of GNU/Linux graphics by Job Smirl.
And then we have the great LWN, which is an essential reference to every linux kernel programmer. There is a bunch of links to the relevant LWN articles and other discussions and slides on thie Linaro Memory Management page.
Again I am a journeyman into Graphics, trying to make sense of various terminologies. There are two pages, that I found helpful.
Hopefully, these links will give a good “big picture” view of the low level parts of rendering/video/graphics inside a modern GNU/Linux desktop. Also remember to watch the date on which this post was written (because The Internet does not forget anything and you, the reader, may be reading this page many months/years after the day this post was written). The display side of things being the most user visible and sensitive thing, is ever changing. The picture may look entirely different after a few years.