How to build a paint application using Arduino

Paint.ino

#include <Adafruit_GFX.h>
#include <MCUFRIEND_kbv.h>
#include "TouchScreen.h" 

#define  BLACK   0x0000
#define BLUE    0x001F
#define RED     0xF800
#define GREEN   0x07E0
#define CYAN    0x07FF
#define MAGENTA 0xF81F
#define YELLOW  0xFFE0
#define WHITE   0xFFFF
MCUFRIEND_kbv tft;

#define MINPRESSURE 10
#define MAXPRESSURE 1000
const int XP=6,XM=A2,YP=A1,YM=7; //320x480 ID=0x9486
const int TS_LEFT=931,TS_RT=168,TS_TOP=452,TS_BOT=191;
#define TS_MINX 125
#define TS_MINY 85
#define TS_MAXX 965
#define TS_MAXY 905
TouchScreen ts(XP, YP, XM, YM, 300);   //re-initialised after diagnose
TSPoint tp; 

#define BOXSIZE 40
unsigned int PENRADIUS = 3;
int oldcolor, currentcolor;

void setup(void) {
  Serial.begin(9600);
  Serial.println(F("Paint!"));

  tft.reset();
  tft.begin(tft.readID());
  Serial.println();
  Serial.print("reading id...");
  delay(500);
  Serial.println(tft.readID(), HEX);
  tft.fillScreen(WHITE);
  
  tft.fillRect(0, 0, BOXSIZE, BOXSIZE, YELLOW);
  tft.fillRect(BOXSIZE, 0, BOXSIZE, BOXSIZE, MAGENTA);
  tft.fillRect(BOXSIZE * 2, 0, BOXSIZE, BOXSIZE, CYAN);
  tft.fillRect(BOXSIZE * 3, 0, BOXSIZE, BOXSIZE, GREEN);
  tft.fillRect(BOXSIZE * 4, 0, BOXSIZE, BOXSIZE, RED);
  tft.fillRect(BOXSIZE * 5, 0, BOXSIZE, BOXSIZE, BLUE);
  tft.fillRect(BOXSIZE * 6, 0, BOXSIZE, BOXSIZE, BLACK);
  tft.fillRect(BOXSIZE * 7, 0, BOXSIZE, BOXSIZE, WHITE);
  tft.drawRect(BOXSIZE * 7, 0, BOXSIZE, BOXSIZE, BLACK);
  currentcolor = YELLOW;
  pinMode(13, OUTPUT);
}

#define MINPRESSURE 10
#define MAXPRESSURE 1000

void loop() {
  digitalWrite(13, HIGH);
  TSPoint p = ts.getPoint();
  digitalWrite(13, LOW);
  pinMode(XM, OUTPUT);
  pinMode(YP, OUTPUT);
  if (p.z > MINPRESSURE && p.z < MAXPRESSURE) {
    if (p.y < (TS_MINY - 5)) {
      Serial.println("erase");
      tft.fillRect(0, BOXSIZE, tft.width(), tft.height() - BOXSIZE, WHITE);
    }
    p.x = map(p.x, TS_MINX, TS_MAXX, tft.width(), 0);
    p.y = map(p.y, TS_MINY, TS_MAXY, tft.height(), 0);
    // Serial.print("X:");  // I used this to get the accurate touch points for X and Y axis
    // Serial.print(p.x);
    // Serial.print("  ");
    // Serial.print("Y:");
    // Serial.println(p.y);
    
    if (p.y < 0) {
      oldcolor = currentcolor;
      if (p.x < BOXSIZE) {
        currentcolor = YELLOW;
        tft.drawRect(0, 0, BOXSIZE, BOXSIZE, WHITE);
      } else if (p.x < BOXSIZE * 2) {
        currentcolor = MAGENTA;
        tft.drawRect(BOXSIZE, 0, BOXSIZE, BOXSIZE, WHITE);
      } else if (p.x < BOXSIZE * 3) {
        currentcolor = CYAN;
        tft.drawRect(BOXSIZE * 2, 0, BOXSIZE, BOXSIZE, WHITE);
      } else if (p.x < BOXSIZE * 4) {
        currentcolor = GREEN;
        tft.drawRect(BOXSIZE * 3, 0, BOXSIZE, BOXSIZE, WHITE);
      } else if (p.x < BOXSIZE * 5) {
        currentcolor = RED;
        tft.drawRect(BOXSIZE * 4, 0, BOXSIZE, BOXSIZE, WHITE);
      } else if (p.x < BOXSIZE * 6) {
        currentcolor = BLUE;
        tft.drawRect(BOXSIZE * 5, 0, BOXSIZE, BOXSIZE, WHITE);
      }else if (p.x < BOXSIZE * 7) {
        currentcolor = BLACK;
        tft.drawRect(BOXSIZE * 6, 0, BOXSIZE, BOXSIZE, WHITE);
      }else if (p.x < BOXSIZE * 8) {
        currentcolor = WHITE;
        tft.drawRect(BOXSIZE * 7, 0, BOXSIZE, BOXSIZE, BLACK);
      }

      if (oldcolor != currentcolor) {
        if (oldcolor == YELLOW) tft.fillRect(0, 0, BOXSIZE, BOXSIZE, YELLOW);
        if (oldcolor == MAGENTA) tft.fillRect(BOXSIZE, 0, BOXSIZE, BOXSIZE, MAGENTA);
        if (oldcolor == CYAN) tft.fillRect(BOXSIZE * 2, 0, BOXSIZE, BOXSIZE, CYAN);
        if (oldcolor == GREEN) tft.fillRect(BOXSIZE * 3, 0, BOXSIZE, BOXSIZE, GREEN);
        if (oldcolor == RED) tft.fillRect(BOXSIZE * 4, 0, BOXSIZE, BOXSIZE, RED);
        if (oldcolor == BLUE) tft.fillRect(BOXSIZE * 5, 0, BOXSIZE, BOXSIZE, BLUE);
        if (oldcolor == BLACK) tft.fillRect(BOXSIZE * 6, 0, BOXSIZE, BOXSIZE, BLACK);
        if (oldcolor == WHITE) tft.fillRect(BOXSIZE * 7, 0, BOXSIZE, BOXSIZE, WHITE);
      }
    }
 
    if ((p.y > 5) && (p.y < tft.height()) && currentcolor != WHITE) {
      PENRADIUS = 3;
      tft.fillCircle((p.x-PENRADIUS), (p.y+BOXSIZE) , PENRADIUS, currentcolor);
    }
    if ((p.y > 5) && (p.y < tft.height()) && currentcolor == WHITE) {
      PENRADIUS = 10;
      tft.fillCircle((p.x-PENRADIUS), (p.y+BOXSIZE) , PENRADIUS, currentcolor);
    }
  }
}