drawing with a finger in iOS

[Ben Rubinstein]

On 26/10/2011 04:00, Andre Garzia wrote:
> I know the paint tools are not supported in iOS but did anyone here
> succeeded in making some paintbrush of sorts for iOS?

I did this for a little prototype (where I wanted to be able to analyse 
hand-drawn lines drawn on top of a background) and it was very easy and had 
good performance (at least on my iPhone4, it never went beyond prototype so 
never got tried elsewhere).

I had a drawing area, and outside it controls for line colour/size and erase 
area - so I think analogous to what you want for a signature area.

My method was to have a 'working image' representing the drawing area, 
translucent over a background; underneath a transparent button that gets the 
events; between the two a normally hidden polygon to display the line 
interactively as the user moves their finger.

On mousedown (cough, I've not yet adapted to the new world of touch events - 
but it works fine) set the points of the line to the mouseloc, show the line. 
  On mouseMove, append the mouseloc to the points of the line.  On mouseUp, I 
hide some extraneous stuff, make the 'working image' opaque, take a snapshot 
of that area (hence compositing the existing drawing with the newly drawn 
line) and then hide the line and replace the working image with that snapshot, 
and adjust the transparency back again.

Changing brush colour and thickness is just a matter of changing the 
properties of the line.

So in short, each touch is handled as it happens by adjusting the points of a 
line object; at the end of the touch, this is composited into a bitmap, 
accumulating all the pixels.  It seems perfectly responsive and robust.

I think it's a fabulous demo of the power of livecode: you can make a working 
iOS paint app with a couple of dozen lines of code.

Ben