Touchscreen software for Raspberry Pi + PiTFT

GUI design has not yet been implemented. Currently that is left up to the programmer.

The GFX module is a heavily modified version of the Adafruit-GFX library. It has been modified for C operation (all of the class members have been prefixed with GFX), and implements the library fully. The library opens a Linux framebuffer interface for a specified resolution (currently hardcoded), and the pixel write function writes directly to the framebuffer RAM. A function is provided to convert 3x bytes into a u16 color. The fast vline and hline functions have been implemented more efficiently. This pair of files (gfx.h and gfx.c) can be used in other projects easily.

The Backlight module is designed to control the backlight of the PiTFT (Resistive version). It currently uses the system calls method, which requires sudo permissions, and is very slow. A better interface would be good. It also provides a timer to automatically turn off the backlight, and a poke function to wake it up/keep it awake.

The Touch module is designed to interface with the /dev/input/touchscreen interface directly. It provides two initialization functions (touch_init and touch_read_kal) which initialize the linux evdev driver and then read the calibration file respectively. A program called kalibrate is provided which uses the touch, gfx, and backlight modules to draw 4 crosshairs on the screen and calibrate from them, and the touch module can read in the calibration. For most applications, both functions should be called to provide display-adjusted data, otherwise the data returned is raw. Note that the Adafruit screen x/y are swapped (or appear to be), so the data returned from the x channel actually came from the y event message, and vice versa, and they are stored in the linux-native name for the cur_x/cur_y variables.

Pressure data is also provided, and is always raw.

The user must call touch_get_events() regularly to read the touch events from the linux buffers. The user can then call touch_get_x, touch_get_y, and touch_get_prs to read the latest x, y, pressure data from the touch screen. The user should read touch_down() before, as an indication of touch data present. Error checking on the x/y/prs outputs when touch_down() is false is not provided.