Adrian Cochrane
Having spent numerous threads describing how computers render visual graphics we can understand, how do they let us interact with those graphics?
The way pointers work at a hardware level is varied. Early models rotated a pair of wheels, hooked up to counters of the number of slots rolling past. Your scrollwheel still often uses this technique. That pretty much directly gives us the data we want but by now we've largely moved away from mechanical techniques to pure electronic techniques.
1/?
Adrian Cochrane
Other popular techniques involves filming a starkly-lit surface texture, computing a Fast Fourier Transform to minimize the data being processed, & aligning the two images to see how far they shifted. And thus what data should be sent to the CPU.
Another popular technique is to have a grid of translucent wires, which might be placed atop the screen such that powering each row lights up the columns where a finger's capacitance overlaps it. Again requires (clustering) preprocessing.
2/3?
Adrian Cochrane
@garritfra Most of them land at: https://adrian.geek.nz/docs
Garrit 🌱
@alcinnz loving these technical threads! Have you considered starting a blog to better reference the topics?
Adrian Cochrane
In either of those cases the device usually has dedicated (signal) processors to preprocess the more verbose data into *more* usable input for the CPU. Linux & LibInput still has plenty of processing to do!
Linux informs your X11 or Wayland window manager of any new devices & their input to determine which application to forward onto. Whether it's your window manager or UI toolkit computers typically represent UIs as a hierarchy of bounding boxes. Making hittesting & layout cheap!
3/4!
Adrian Cochrane
If those axis-aligned bounding boxes crop their children, UI toolkits immediately know which branch to dispatch the input down. Or for more complex cases you can use the GPU to offscreen-render a lookuptable.
There's several different layout formulas, but they all boil down to geometry.
Ofcourse UI toolkits also respond to keyboard or mouse button presses. Whilst defining a shared language with users.
A "mainloop" puts users in charge of controlflow by repeatedly asking them what to do.
4/4
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