touchable ????????

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

Index :

• Why Use Touchable ?
• Installation
• Usage
• How it works
• Road Map 
• Links

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.

Installation

Add the touchable package as dependency in your pubspec.yaml

dependencies:
  touchable:

---

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 contextobtained 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.points , 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.round 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
•  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

Download Flutter gesture callbacks library source code on GitHub

https://github.com/nateshmbhat/touchable