Question

I am having some serious troubles implementing a draw in the scala language. my current code looks like:

package edu.luc.cs.laufer.cs473.shapealgebra

import java.awt.Graphics2D

class Draw {
  def draw(g: Graphics2D)(s: Shape): Unit = s match {
    case Ellipse(hw, hh) => g.drawArc(-hw, -hh, 2 * hw, 2 * hh, 0, 360)
    case Rectangle(w, h) => g.drawRect(0, 0, w, h)
    case Location(x: Int, y: Int, shape: Shape) => {
      g.translate(x, y)
      draw(g)(shape)
      g.translate(0,0)
    }
    case Group(shapes @ _*) => {
      shapes foreach(draw(g)(_))
    }
  }
 }

 object Draw extends Draw {
  def apply(g: Graphics2D) = draw(g)(_)
}

The problem here is with my group case. It does not draw a group of shapes properly. The two test cases uses the following shapes:

val simpleLocation = Location(70, 30, Rectangle(80, 120))
val complexGroup = Location(50, 100,
    Group(
     Ellipse(20, 20),
     Location(150, 50,
        Group(
          Rectangle(50, 30),
          Rectangle(300, 60),
          Location(100, 200,
          Ellipse(50, 50)
         )
       )
     ),
     Rectangle(100, 200)
   )
  )

The complex continues to fail and I can’t figure out why.

package edu.luc.cs.laufer.cs473.shapealgebra

import org.junit.runner.RunWith
import org.scalatest.junit.JUnitRunner
import org.scalatest.FunSuite

import java.awt.image.BufferedImage

import TestFixtures._

@RunWith(classOf[JUnitRunner])
class TestDraw extends FunSuite with BufferedImageEquality {
  test("simple") {
    val s = simpleLocation
    val i = new BufferedImage(500, 500, BufferedImage.TYPE_INT_RGB)
    Draw(i.createGraphics())(s)
    val j = new BufferedImage(500, 500, BufferedImage.TYPE_INT_RGB)
    val g = j.createGraphics()
    g.translate(70, 30)
    g.drawRect(0, 0, 80, 120)
    assertEquals(i, j)
  }
  test("complex") {
    val s = complexGroup
    val i = new BufferedImage(500, 500, BufferedImage.TYPE_INT_RGB)
    Draw(i.createGraphics())(s)
    val j = new BufferedImage(500, 500, BufferedImage.TYPE_INT_RGB)
    val g = j.createGraphics()
    paintComplexGroup(g)
        assertEquals(i, j)
  }
}

The test case is shown above. I get a “0 did not equal 255” from the result of the unit test.

Answer 1

If you look at what translate does, the Javadoc says

“Translates the origin of the Graphics2D context to the point (x, y)
in the current coordinate system.”

So

  g.translate(0,0)

does nothing. Try

  g.translate(-x, -y)

Although, if it were me, I wouldn’t mess with the Graphics object’s origin. I’d modify the drawRect and drawArc statements to take a location, and pass the location co-ordiates as an argument to the method.