Canvas DrawLine "xor" RemoveLine

[andyhill]

I am trying to draw a rectangle polyline over a canvas containing a color image, then (via way of a mouse drag move event) remove that rectangle polyline with it's original points and redraw as a new rectangle polyline using the new x,y co-ordinates. Code below paints with or without "xor", my problem is it will not erase when using the same points, happy for any help - Thanks - Andy

    UniSession.AddJS('var context=fMain.cArea._cc_; '+
                     'var polyln = ['+s+']; '+
                     'var shape = polyln.slice(0); '+
                     '{ '+
                     '  context.globalAlpha = 1; '+
                     '  context.globalCompositeOperation = ''xor''; '+
                     '  context.lineWidth = 1; '+
                     '  context.strokeStyle = "'+LineColourStr+'"; '+
                     '  context.moveTo(shape.shift(), shape.shift()); '+
                     '  while(shape.length) '+
                     '  { '+
                     '    context.lineTo(shape.shift(), shape.shift()); '+
                     '  } '+
                     '  context.stroke(); '+
                     '  context.globalCompositeOperation = ''source-over''; '+
                     '  context.globalAlpha = 1; '+
                     '}; '
                    );

 

[Sherzod]

10 hours ago, andyhill said:

I am trying to draw a rectangle polyline over a canvas containing a color image, then (via way of a mouse drag move event) remove that rectangle polyline with it's original points and redraw as a new rectangle polyline using the new x,y co-ordinates. Code below paints with or without "xor", my problem is it will not erase when using the same points, happy for any help - Thanks - Andy

Hello,

Do you have a simple testcase to test?

[andyhill]

I experimented with Alpha and XOR.

Please see README.txt and RequiredResult.jpg showing DrawClosedPolyLine once to show, then once to remove.

1) Fill does not work for me ?

2) XOR in my mind should erase ?

Project1.zip

[andyhill]

Added "context.fill();" now fills fine.

Sherzod, please advise how to draw then erase (draw works fine).