touchable 👆🏻 #

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

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 of your drawing. So , when your paint is filled ▮ it registers touch on the entire shape else when its stroke ▯ , it looks for gesture only on the borders.

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

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

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

Installation #

Add the following package in your pubspec.yaml

dependencies:
  touchable: ^0.1.2

Usage : #

• Just Wrap your CustomPaint widget with CanvasTouchDetector. It takes a builder function as argument that expects your CustomPaint widget as shown below.

CanvasTouchDetector(
    builder: (context) => 
        CustomPaint(
            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

  @override
  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");
       },
        onPanDown:(tapdetail){
          print("orange circle swiped");
        } 
    );

    myCanvas.drawLine(
        Offset(0, 0),
        Offset(size.width - 100, size.height - 100),
        Paint()
          ..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 #

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