ILI9488 TFT Touchscreen Calibration

#include "SPI.h"
#include "Adafruit_GFX.h"
#include <ILI9488.h>
#include "XPT2046_Touchscreen.h"
#include "Math.h"

#define TFT_CS 10
#define TS_CS 7

#define ROTATION 3

ILI9488 tft = ILI9488(/*TFT_CS*/ 10, /*TFT_DC*/ 9, /*TFT_MOSI*/ 11, /*TFT_CLK*/ 13, /*TFT_RST*/ 8, /*TFT_MISO*/ 12);

XPT2046_Touchscreen ts(TS_CS);

// calibration values
float xCalM = 0.0, yCalM = 0.0;  // gradients
float xCalC = 0.0, yCalC = 0.0;  // y axis crossing points

int8_t blockWidth = 20;  // block size
int8_t blockHeight = 20;
int16_t blockX = 0, blockY = 0;  // block position (pixels)

class ScreenPoint {
public:
  int16_t x;
  int16_t y;

  // default constructor
  ScreenPoint() {
  }

  ScreenPoint(int16_t xIn, int16_t yIn) {
    x = xIn;
    y = yIn;
  }
};

ScreenPoint getScreenCoords(int16_t x, int16_t y) {
  int16_t xCoord = round((x * xCalM) + xCalC);
  int16_t yCoord = round((y * yCalM) + yCalC);
  if (xCoord < 0) xCoord = 0;
  if (xCoord >= tft.width()) xCoord = tft.width() - 1;
  if (yCoord < 0) yCoord = 0;
  if (yCoord >= tft.height()) yCoord = tft.height() - 1;
  return (ScreenPoint(xCoord, yCoord));
}

void calibrateTouchScreen() {
  TS_Point p;
  int16_t x1, y1, x2, y2;

  tft.fillScreen(ILI9488_YELLOW);

  // wait for no touch
  while (ts.touched()) Serial.println("...");

  tft.drawFastHLine(10, 20, 20, ILI9488_RED);
  tft.drawFastVLine(20, 10, 20, ILI9488_RED);

  while (!ts.touched())
  delay(50);
  p = ts.getPoint();
  x1 = p.x;
  y1 = p.y;
  tft.drawFastHLine(10, 20, 20, ILI9488_BLACK);
  tft.drawFastVLine(20, 10, 20, ILI9488_BLACK);
  delay(500);

  while (ts.touched())

  tft.drawFastHLine(tft.width() - 30, tft.height() - 20, 20, ILI9488_RED);
  tft.drawFastVLine(tft.width() - 20, tft.height() - 30, 20, ILI9488_RED);

  while (!ts.touched())
  delay(50);
  p = ts.getPoint();
  x2 = p.x;
  y2 = p.y;
  tft.drawFastHLine(tft.width() - 30, tft.height() - 20, 20, ILI9488_BLACK);
  tft.drawFastVLine(tft.width() - 20, tft.height() - 30, 20, ILI9488_BLACK);

  int16_t xDist = tft.width() - 40;
  int16_t yDist = tft.height() - 40;

  // translate in form pos = m x val + c
  // x
  xCalM = (float)xDist / (float)(x2 - x1);
  xCalC = 20.0 - ((float)x1 * xCalM);
  // y
  yCalM = (float)yDist / (float)(y2 - y1);
  yCalC = 20.0 - ((float)y1 * yCalM);

  Serial.print("x1 = ");
  Serial.print(x1);
  Serial.print(", y1 = ");
  Serial.print(y1);
  Serial.print("x2 = ");
  Serial.print(x2);
  Serial.print(", y2 = ");
  Serial.println(y2);
  Serial.print("xCalM = ");
  Serial.print(xCalM);
  Serial.print(", xCalC = ");
  Serial.print(xCalC);
  Serial.print("yCalM = ");
  Serial.print(yCalM);
  Serial.print(", yCalC = ");
  Serial.println(yCalC);
}


void setup() {
  Serial.begin(115200);

  // while(!Serial)

  Serial.println("Setup starts.");

  // avoid chip select contention
  pinMode(TS_CS, OUTPUT);
  digitalWrite(TS_CS, HIGH);
  pinMode(TFT_CS, OUTPUT);
  digitalWrite(TFT_CS, HIGH);

  tft.begin();
  tft.setRotation(ROTATION);
  tft.fillScreen(ILI9488_BLUE);

  ts.begin();
  ts.setRotation(ROTATION);

  tft.fillScreen(ILI9488_RED);

 // calibrateTouchScreen();

  Serial.println("Setup ends.");
}

void moveBlock() {
  int16_t newBlockX = 0, newBlockY = 0;
  ScreenPoint sp = ScreenPoint();
  if (ts.touched()) {
    TS_Point p = ts.getPoint();
    sp = getScreenCoords(p.x, p.y);
    newBlockX = sp.x - (blockWidth / 2);
    newBlockY = sp.y - (blockHeight / 2);
    if (newBlockX < 0) newBlockX = 0;
    if (newBlockX >= (tft.width() - blockWidth)) newBlockX = tft.width() - 1 - blockWidth;
    if (newBlockY < 0) newBlockY = 0;
    if (newBlockY >= (tft.height() - blockHeight)) newBlockY = tft.height() - 1 - blockHeight;
  }
  if ((abs(newBlockX - blockX) > 2) || (abs(newBlockY - blockY) > 2)) {
    tft.fillRect(blockX, blockY, blockWidth, blockHeight, ILI9488_BLACK);
    blockX = newBlockX;
    blockY = newBlockY;
    tft.fillRect(blockX, blockY, blockWidth, blockHeight, ILI9488_RED);
  }
}

unsigned long lastFrame = millis();

void loop(void) {

  // limit frame rate
  while ((millis() - lastFrame) < 20);
  lastFrame = millis();

  if (ts.touched()) {
    moveBlock();
  }
}