Flutter Canvas Draw Library

Flutter Canvas Draw Library

touchable 👆🏻

Flutter library to add various gesture callbacks to each Shape you draw on your canvas in your CustomPainter

Flutter Canvas Draw Library Flutter Canvas Draw Library

Index :

Why Use Touchable ?

  • The CustomPainter lets you only draw shapes on the canvas. But most would want to let user interact with the drawings.

  • With touchable , you get what the normal canvas always missed : touchability 😉

  • With this , its possible to add all kinds of gesture callbacks to each drawing and thus interaction capability to each Shape you draw on the canvas.

  • Animating individual shapes becomes so much easier than ever before.

  • Handles the painting style (filled ▮ , stroke ▯) and detects touch accordingly.

  • Takes the painting stroke width also into account. So if your shapes are painted thick , we still got it covered ✓

  • Supports clipping and different clipping modes. So, You can have any kind of complex clipping and drawing combinations while getting full interactive capability.

  • Supports HitTestBehavior for each shape.

  • Simple and Easy API. Just wrap your CustomPaint with CanvasTouchDetector and use the TouchyCanvas in your painter.


Add the touchable package as dependency in your pubspec.yaml


Usage :

  • Just Wrap your CustomPaint widget with CanvasTouchDetector. It takes a builder function as argument that expects your CustomPaint widget as shown below.
    builder: (context) => 
            painter: MyPainter(context)
  • Inside your CustomPainter class’s paint method , create and use the TouchyCanvas object (using the context obtained from the CanvasTouchDetector and canvas) to draw any shape with different gesture callbacks.
var myCanvas = TouchyCanvas(context,canvas);
myCanvas.drawRect( rect , Paint() , onTapDown: (tapDetail){
    //Do stuff here. Probably change your state and animate

MyPainter example :

class MyPainter extends CustomPainter {

  final BuildContext context ;
  MyPainter(this.context); // context from CanvasTouchDetector

  void paint(Canvas canvas, Size size) {
    var myCanvas = TouchyCanvas(context,canvas); 

    myCanvas.drawCircle(Offset(10, 10), 60, Paint()..color=Colors.orange ,
        onTapDown: (tapdetail) {
         print("orange Circle touched");
          print("orange circle swiped");

        Offset(0, 0),
        Offset(size.width - 100, size.height - 100),
          ..color = Colors.black
          ..strokeWidth = 50, 
        onPanUpdate: (detail) {
            print('Black line Swiped'); //do cooler things here. Probably change app state or animate

How Touchable Works :

When you draw shapes on the canvas (TouchyCanvas) , it keeps track of the dimensions of each shape you draw and their painting style , stroke etc.

When user performs any gesture on the screen , based on the location of the gesture , the appropriate shape is selected from the lot taking clipping regions , paint , hitTest behaviour etc into account in an optimized way. Callbacks of the corresponding shapes (one or more depending on the hitTest behavior) are executed.

Road Map

  • [x] Basic Shape Detection
    • [x] Line
    • [x] Rectangle (Rect)
    • [x] Circle
    • [x] Oval or Ellipse
    • [x] Arc
    • [x] segment
    • [x] sector
    • [x] Rounded Rectangle (RRect)
    • [x] Custom Path [only supports opaque hittest]
    • [x] Points (PointMode.points , PointMode.lines , PointMode.polygon)
    • [ ] Vertices
    • [ ] Traingle
    • [ ] Traingle Strip
    • [ ] Traingle Fan
  • [x] Support for proper edge detection based on the Paint object properties :
    • [x] Paint style
    • [x] Stroke Width
    • [ ] Stroke Cap
    • [x] StrokeCap to draw Points
    • [ ] StrokeCap.round for lines with large width
  • [x] Support Clipping and clipping modes
    • [x] ClipRect
    • [x] intersect mode [Touch detection enabled only inside the clipped region]
    • [x] difference mode [Touch detection enabled only outside the clipped region]
    • [x] ClipRRect
    • [x] ClipPath
  • [x] Support for HitTestBehavior
  • [ ] Make the touch detection handling to run in a seperate isolate.
  • [ ] Support for translation , rotation , scaling and skewing transformations that needs some vector math

Links :

Source Code

Please Visit Flutter Canvas Draw Library Source Code at GitHub