The LCD has a 2.8" 4-wire resistive touch screen glued onto it. You can use this for detecting finger-presses, stylus', etc. Normally, you'll need 4 pins to talk to the touch panel but we decided to go all snazzy and put a dedicated touch screen driver onto the shield. The driver shares the SPI pins with the TFT and SD card, so only one extra pin is needed (digital #8) This allows you to query the controller when you're ready to read touchscreen data, and saves 3 pins.
To control the touchscreen you'll need one more library - the STMPE610 controller library which does all the low level chatting with the STMPE610 driver chip.
Adafruit_STMPE610 ts = Adafruit_STMPE610(STMPE_CS);We're using hardware SPI so the clock, mosi and miso pins are not defined here. For the shield, CS is #8 always.
Then you can start the touchscreen with
ts.begin()Check to make sure this returns a True value, which means the driver was found. If it wasn't, make sure you have the hardware SPI jumpers set up right: for Leonardo/Mega the ICSP jumpers get closed.
Now you can call
if (! ts.bufferEmpty())to check if there's any data in the buffer. The touchscreen driver will store touchpoints at all times. When you're ready to get the data, just check if there's any data in the buffer. If there is, you can call
TS_Point p = ts.getPoint();To get the oldest point from the buffer. TS_Point has .x .y and .z data points. The x and y points range from 0 to 4095. The STMPE610 does not store any calibration data in it and it doesn't know about rotation. So if you want to rotate the screen you'll need to manually rotate the x/y points! The z point is 'pressure' and ranges from 0 to 255, we don't use it here but you can experiment with it on your own, the harder you press, the lower the number.
Since data from the STMPE610 comes in 0-4095 but our screen is 320 pixels by 240 pixels, we can use map to convert 0-4095 to 0-320 or 0-240. Something like
p.x = map(p.x, 0, 4095, 0, tft.width());However, the touchscreen is a bit bigger than the screen, so we actually need to ignore presses beyond the touchscreen itself. We found that these numbers reflected the true range that overlaps the screen
p.y = map(p.y, 0, 4095, 0, tft.height());
#define TS_MINX 150So we use
#define TS_MINY 130
#define TS_MAXX 3800
#define TS_MAXY 4000
p.x = map(p.x, TS_MINX, TS_MAXX, 0, tft.width());instead.
p.y = map(p.y, TS_MINY, TS_MAXY, 0, tft.height());
One last point (pun intended!) since the touchscreen driver stores points in a buffer, you may want to ask the driver "is the touchscreen being pressed RIGHT NOW?" You can do that with