ESP32 ILI9488 touch paint

// Touch paint on a 3.5 inch ILI9488 TFT (320x480) with an ESP32 and TFT_eSPI.
//
// TFT_eSPI reads its driver and pins from User_Setup.h. In Mokxi they are
// #defines above the #include, with the same names: these lines are what
// goes in User_Setup.h on the bench.
//
// The ILI9488 has no 16-bit color mode over SPI, so TFT_eSPI sends it 18-bit
// color, three bytes a pixel. The display's MISO is left unconnected: the
// ILI9488 never lets go of that line, and the touch controller (an XPT2046
// on the same SCK and MOSI, with its own chip select) answers on GPIO 19.
#define ILI9488_DRIVER
#define TFT_MISO 19
#define TFT_MOSI 23
#define TFT_SCLK 18
#define TFT_CS   15
#define TFT_DC    2
#define TFT_RST   4
#define TOUCH_CS 21

#include <TFT_eSPI.h>

TFT_eSPI tft = TFT_eSPI();

const uint16_t COLORS[8] = {TFT_RED, TFT_ORANGE, TFT_YELLOW, TFT_GREEN, TFT_CYAN, TFT_BLUE, TFT_MAGENTA, TFT_WHITE};
const int SWATCH = 40;   // eight swatches across the 320-pixel width
const int TOP = 80;      // the canvas starts below the palette and the title
uint16_t ink = TFT_YELLOW;

// The raw readings at the edges of the glass: the touch film is a little
// bigger than the picture, so it reads about 200 to 3900, not 0 to 4095.
// The film is laminated to the glass, and rotation 0 (MADCTL's MX) draws the
// columns from the glass's far edge, so a bigger raw X is further left: the
// X map runs backwards. Calibrate a real panel with tft.calibrateTouch().
const int RAW_MIN = 205;
const int RAW_MAX = 3890;

void drawPalette() {
  for (int i = 0; i < 8; i++) {
    tft.fillRect(i * SWATCH, 0, SWATCH, SWATCH, COLORS[i]);
    if (COLORS[i] == ink) tft.drawRect(i * SWATCH + 2, 2, SWATCH - 4, SWATCH - 4, TFT_BLACK);
  }
}

void clearCanvas() {
  tft.fillRect(0, TOP, 320, 480 - TOP, TFT_BLACK);
  tft.drawRect(0, TOP, 320, 480 - TOP, TFT_DARKGREY);
}

void setup() {
  Serial.begin(115200);
  tft.init();
  tft.setRotation(0);  // portrait, 320x480
  tft.fillScreen(TFT_BLACK);
  drawPalette();
  tft.setTextColor(TFT_WHITE, TFT_BLACK);
  tft.drawString("Pick a color, draw below. Tap here to clear.", 6, 52, 2);
  tft.drawRect(0, TOP, 320, 480 - TOP, TFT_DARKGREY);  // the screen is already black
  Serial.print("TFT ");
  Serial.print(tft.width());
  Serial.print("x");
  Serial.println(tft.height());
}

void loop() {
  // Pressure first: with nothing pressed, X and Y mean nothing.
  if (tft.getTouchRawZ() < 300) return;
  uint16_t rx, ry;
  tft.getTouchRaw(&rx, &ry);
  int x = constrain(map(rx, RAW_MAX, RAW_MIN, 0, 319), 0, 319);
  int y = constrain(map(ry, RAW_MIN, RAW_MAX, 0, 479), 0, 479);

  if (y < SWATCH) {
    ink = COLORS[x / SWATCH];
    drawPalette();
    Serial.print("ink ");
    Serial.println(x / SWATCH);
    delay(200);
  } else if (y < TOP) {
    clearCanvas();
    Serial.println("cleared");
    delay(200);
  } else {
    tft.fillCircle(x, y, 4, ink);
    Serial.print("dot ");
    Serial.print(x);
    Serial.print(",");
    Serial.println(y);
  }
}