Totalcross - Whiteboard starts dash with difference from the point initially pressed

     case PenEvent.PEN_DOWN:
        pe = (PenEvent)event;
        oldX = pe.x;
        oldY = pe.y;
        yIni = pe.y;       <=======
        drawTo(gImg, pe.x,pe.y); // after
        if (gScr != null) drawTo(gScr,pe.x,pe.y);
        getParentWindow().setGrabPenEvents(this); // guich@tc100: redirect all pen events to here, bypassing other processings
        if (Settings.isOpenGL) te = addTimer(100);
        break;
     case PenEvent.PEN_DRAG:
        pe = (PenEvent)event;
        if (yIni>0) {                
            yDif = yIni -pe.y;         
            yIni = 0;                 
        }
        drawTo(gImg, pe.x,pe.y + yDif); // before
        if (gScr != null) drawTo(gScr, pe.x, pe.y + yDif);  
        oldX = pe.x;
        oldY = pe.y + yDif;
        if (!Settings.isOpenGL) Window.safeUpdateScreen(); // important at desktop!
        break;

I set the routine this way, I calculated the difference of the pe.y of the PEN_DOWN event with the pe.y of the PEN_DRAG event and applied it to the pe.y to draw the line.

The Whiteboard class works with the concept of several small strokes. At every moment, it captures the point where the touch is and draws a line compared to the previous point.

The magic of this concept of small dashes on the screen is in the drawTo method within Whiteboard ; given a new point, knowing the previous point, draw the line:

private void drawTo(Graphics g, int pex, int pey)
{
    g.drawLine(oldX,oldY,pex,pey); // guich@580_34: draw directly on screen
    if (thick)
    {
        g.drawLine(oldX+1,oldY+1,pex+1,pey+1);
        g.drawLine(oldX-1,oldY-1,pex-1,pey-1);
        g.drawLine(oldX+1,oldY+1,pex-1,pey-1);
        g.drawLine(oldX-1,oldY-1,pex+1,pey+1);
    }
}

  

Note: if you are turned on to make a thick drawing, it will make an additional set of parallel lines, as seen in if (thick) .

In the case of the first touch (event of type PEN_DOWN ), it ends up drawing a segment of zero pixels , which turns a dot on the screen:

public onEvent(Event event)
{
    PenEvent pe;
    switch (event.type)
    {
    [...]
    case PenEvent.PEN_DOWN:
        pe = (PenEvent)event;
        oldX = pe.x;
        oldY = pe.y;
        drawTo(gImg, pe.x,pe.y); // after
        if (gScr != null) drawTo(gScr,pe.x,pe.y);
        getParentWindow().setGrabPenEvents(this); // guich@tc100: redirect all pen events to here, bypassing other processings
        if (Settings.isOpenGL) te = addTimer(100);
        break;
    [...]
} [fim do onEvent]

When dragging the touch (event of type PEN_DRAG ), each drag capture Whiteboard will make a stroke from the previous touch to the current touch:

public onEvent(Event event)
{
    PenEvent pe;
    switch (event.type)
    {
    [...]
    case PenEvent.PEN_DRAG:
        pe = (PenEvent)event;
        drawTo(gImg, pe.x,pe.y); // before
        if (gScr != null) drawTo(gScr,pe.x,pe.y);
        oldX = pe.x;
        oldY = pe.y;
        if (!Settings.isOpenGL) Window.safeUpdateScreen(); // important at desktop!
        break;
    [...]
} [fim do onEvent]

In this case, the sensitivity of where the system picks up the click point ( pe.x and pe.y ) depends on your finger and also on the device. Until the current time and the tests performed, the accuracy has been quite satisfactory.

public onEvent(Event event) 
{
    PenEvent pe; 
    switch (event.type) 
    { 
    [...] 
    case PenEvent.PEN_DOWN: 
        pe = (PenEvent)event; 
        oldX = pe.x; 
        oldY = pe.y;
        drawTo(gImg, pe.x,pe.y); // after 
        if (gScr != null) drawTo(gScr,pe.x,pe.y);
      //  getParentWindow().setGrabPenEvents(this); // guich@tc100: redirect all //pen events to here, bypassing other processings
        if (Settings.isOpenGL) te = addTimer(100);
        break;
    [...]
} [fim do onEvent]

Include the class in the project and after debugging, I commented the line with the

getParentWindow().setGrabPenEvents(this);

and worked correctly as expected.

What should I have done so that it was not necessary to comment on this line ???