Project: Scribble

Step 1 Paint Rectangle

import java.awt.{Color, Graphics2D}
import scala.swing.BorderPanel.Position.Center
import scala.swing.{BorderPanel, Dimension, MainFrame, Panel, SimpleSwingApplication}

object Scribble1 extends SimpleSwingApplication:
  def top = new MainFrame:
    title = "Scribble App"

    object canvas extends Panel:
      override def paintComponent(g: Graphics2D): Unit =
        super.paintComponent(g)
        g.setColor(Color.black)
        g.drawRect(20, 20, 20, 20)

    contents = new BorderPanel:
      layout(canvas) = Center
    size = new Dimension(500, 500)

step 2 Mouse Events

add the mouse events to the canvas

object canvas extends Panel:
  listenTo(mouse.clicks)
  var x1 = 0
  var y1 = 0
  var x2 = 0
  var y2 = 0

  reactions +=
    case e: MousePressed =>
      x1 = e.point.x
      y1 = e.point.y

    case e: MouseReleased =>
      x2 = e.point.x
      y2 = e.point.y
      repaint()

step 3: Rectangle class

class Rect(var x1: Int, var y1: Int, var x2: Int, var y2: Int):
  def draw(g: Graphics2D): Unit =
    g.drawRect(x1, y1, x2 - x1, y2 - y1)

step 4 Shape trait

trait Shape:
  var x1: Int
  var y1: Int
  var x2: Int
  var y2: Int
  def draw(g: Graphics2D): Unit

Also create an Oval class

step 5 More shapes

private val shapes: ListBuffer[Shape] = ListBuffer()

case e: MousePressed =>
  if e.triggersPopup then
    shp = Oval(e.point.x, e.point.y, 0, 0)
  else
    shp = Rect(e.point.x, e.point.y, 0, 0)

  shapes.append(shp)

step 6 Button Panel

val modePanel = new FlowPanel:
  val rectangleButton = new Button("Rectangle")
  val ovalButton = new Button("Oval")

  contents += rectangleButton
  contents += ovalButton

  listenTo(rectangleButton, ovalButton)

  reactions += {
    case ButtonClicked(`rectangleButton`) => currentMode = Rectangle
    case ButtonClicked(`ovalButton`) => currentMode = Oval
  }
  // backticks: In pattern matching, it helps you to use variable as if its a concrete value.