Add support for 'rolling scrolling' to HX8357D pitft driver. #15
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added 3 commits
November 29, 2017 00:07
…n a window. Add a sysfs param scroll_pos which sets the scanline where the display starts for 'rolling scrolling'. This needs support from the specific display driver as well. When supported it can be used to implement smooth vertical (when the display is in portrait mode) hor horizontal (when the display is used in landscape mode) scrolling by strategically changing the start scanline of the display and erasing/redrawing only the wrapping part. This way you never need to redraw what's already there, preventing slow full screen redraws over spi.
Writing to registers of the device directly from the sysfs store handler leads to race conditions with updating the screen. Just set the variable and update the scroll pos from the next update_display call. This means the scrolling might not actually happen until you draw something to the screen. But as scrolling without drawing a new scanline is not very useful anyway this is a minor annoyance.
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It's nice to be able to have somewhat smooth scrolling, despite the slow(ish) spi connection. |
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When you want to scroll your display by just redrawing it all the time it is very slow (fullscreen redraws over spi are quite slow). However, the HX8357D (and others probably too) chipset supports hardware scrolling.
(horizontal wraparounf scrolling in landscape mode, or vertical in portrait)
This changeset adds a sysfs param to set the start scanline. by changing the start scanline the whole display is scrolled. You then only need to redraw the wrapped around scanlines instead of the whole screen.