Interpolating function for two points on TFT-Screen

Projects Programming
1

Hello,

Currently I am trying to write an interpolating function, which connects individual dots I draw on my TFT ILI9341 Touch Screen. For some reason though, it behaves in a really buggy way.. It connects points at different parts, not where I draw and it behaves in a random way. It also stops working when I approach the maximum X value. Could anyone help me correcting my linearInterpolation function? I would be happy about any help! thank you. :slight_smile:

My Display.cpp:

#include "Display.h"

// XPT2046_Touchscreen ts(CS_PIN); // Instanziierung eines ts Objekts der Klasse XPT2046_Touchscreen
// ILI9341_t3 tft = ILI9341_t3(TFT_CS, TFT_DC);
#define TIRQ_PIN 2
#define CS_PIN 8
#define TFT_DC 9
#define TFT_CS 10

Display::Display() : ts(CS_PIN), tft(TFT_CS, TFT_DC)
{
}

// Original raw minimum and maximum values:
// X --> 340 bis 3900
// Y --> 200 bis 3850

boolean Display::isTouched()
{
    return touched = ts.touched();
}

int Display::getX()
{
    if (touched)
    {
        TS_Point p = ts.getPoint(); // point getter function
        {
            if (map(p.x, 340, 3900, 320, 0) <= 320)
            {
                return map(p.x, 340, 3900, 320, 0);
            }
            else if (map(p.x, 340, 3900, 320, 0) > 320)
            {
                return maximumX;
            }
            else if (map(p.x, 340, 3900, 320, 0) < 0)
            {
                return minimumX;
            }
            else
            {
                {
                    //   return _beyondDisplay;
                }
            }
        }
    }
}

int Display::getY()
{
    if (touched)
    {
        TS_Point p = ts.getPoint(); // point getter function
        {
            if (map(p.y, 200, 3850, 240, 0) <= 240)
            {
                return map(p.y, 200, 3850, 240, 0);
            }
            else if (map(p.y, 200, 3850, 240, 0) > 240)
            {
                return maximumY;
            }
            else if (map(p.y, 200, 3850, 240, 0) < 0)
            {
                return minimumY;
            }
            else
            {
                //      return _beyondDisplay;
            }
        }
    }
}

void Display::drawButtons()
{
    for (int i{0}; i < 4; ++i)
    {
        tft.fillRoundRect(_gap + (_gap + _widthSquare) * i, 220, _widthSquare, _heightSquare, _radiusOfRoundCorner, CL(250, 0, 0));
        tft.setCursor(26 + ((_gap + _widthSquare) * i), 227);
        tft.print(buttonNames[i]);
    }
    tft.drawLine(0, 120, 320, 120, CL(255, 255, 255));
    tft.drawLine(0, 121, 320, 121, CL(255, 255, 255));
    tft.drawLine(0, 119, 320, 119, CL(255, 255, 255));
}

void Display::clear()
{
    tft.fillScreen(ILI9341_BLACK);
    drawButtons();
}

void Display::start()
{
    Serial.begin(38600);
    tft.begin();
    tft.setRotation(1);
    tft.fillScreen(ILI9341_BLACK);
    ts.begin();
    ts.setRotation(1);
    while (!Serial && (millis() <= 1000))
        ; // weiß nicht was das ist
}

boolean Display::pointInRect(int x, float y, float rectX, float rectY, float rectW, float rectH)
{
    boolean ret = false;
    if ((x >= rectX) && (x <= (rectX + rectW)) && (y >= rectY) && (y <= (rectY + rectH)))
    {
        ret = true;
    }
    return ret;
}

void Display::touchButton()
{
    if (pointInRect(_x, _y, _gap, (240 - _heightSquare), (_widthSquare), (_heightSquare)))
    {
        tft.fillRoundRect(_gap, (240 - _heightSquare), _widthSquare, _heightSquare, _radiusOfRoundCorner, CL(250, 100, 0));
        clear();
        // clearArray();
    }
}

void Display::draw(int x, int y)
{
    wave1Values[map(x, 0, 320, 0, 256)] = map(y, 0, 240, -32767, 32767);

    for (int i{0}; i < 257; ++i)
    {
        tft.fillCircle(map(i, 0, 256, 0, 320), map(wave1Values[i], -32767, 32767, 0, 240), pointRadius, CL(255, 0, 0));
    }
}


void Display::linearInterpolation()
{
    Serial.println(getX());
     for (int i = X_old; i < getX();)
    {
        if (X_old <= getX())
        {
            i++;
        }
        else
        {
            i--;
        }
        wave1Values[i] = map(i, X_old, getX(), wave1Values[map(X_old, 0, 320, 0, 256)], wave1Values[map(getX(), 0, 320, 0, 256)]);
    }  
    X_old = getX();
}

Relevant loop part of my main code:

void loop ()
{
  if (display.isTouched())
  {
    Serial.println(display.getX());
    if (previousIsTouched)
    {
      display.linearInterpolation();
    }
    display.touchButton();
    display.clear();
    display.draw(display.getX(), display.getY());
  }
  previousIsTouched = display.isTouched();

  sequencer.stepButtons();
  sequencer.stepLED();
}
2

connects individual dots I draw on my TFT

Do you mean draw a line between them? If so, why not just call the line draw function?

3

There are literally thousands of examples of line drawing algorithms available online, and nearly all will do interpolation, most using the Bresenham algorithm. Why re-invent the wheel?

4

Thank you guys, you are both right, I will look up the Bresenham algorithm and also try it with the drawLine function!

5

For a start this loop assumes you only ever increase X:

     for (int i = X_old; i < getX();)

yet in the loop body you explicitly check for direction:

        if (X_old <= getX())
        {
            i++;
        }
        else
        {
            i--;
        }

so clearly the existing attempt isn't consistent...

6

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