Shape coordenates

General
1

Is there a reason why X,Y coordinates on 2D objects are the object center and in Graphics the X, Y are the coordinates of the top-left corner?

image

Canvas 1

Sub Paint(g As Graphics, areas() As Rect) Handles Paint
  g.DrawRectangle(0,0,Me.Width,Me.Height)
  g.DrawingColor=Color.Gray
  g.FillRectangle(30,30,30,30)
End Sub

Canvas 2

Sub Paint(g As Graphics, areas() As Rect) Handles Paint
  g.DrawRectangle(0,0,Me.Width,Me.Height)
  
  Var px As New RectShape
  px.Height=30
  px.Width=30
  px.x = 30
  px.y = 30
  px.FillOpacity=50
  g.DrawObject(px)
End Sub
1 Like
2

Reason? Nah, just how the objects are architected. I don’t know for sure but I suspect they’re trying to ape how SVG/HTML elements operate.

3

Shapes coordinate are relative to its center,
rectangle and path objects are relative to top left point

4

The main reason is so that they can be easily rotated and scaled since both of these operations tend to happen around the center point.

5

So all rectangles must be drawn as follows to get positioned at x=10 and y=10?

Var a As New roundRectShape
a.X = 10+(a.Width/2)
a.Y=10+(a.Height/2)
a.Height = 100
a.Width = 100
g.DrawObject(a,100,100)

This sample from the docs will show no text as it is off the top of the picture.

Var a As New TextShape
a.Text = "Hello World!"
a.X = 100
g.DrawObject(a)

or will show only the right half of the text when X=1 and Y=20.

SVG places the X and Y at the Top and Left of objects.
It uses CX and CY for centers, and a radius for each.

Is there some introductory documentation to this?