GAMBAS BOOK 3.19.1

In this chapter, the explanations on the topic of 'Drawing with methods of the Paint class' are implemented in two specific projects. Almost all drawings are based on script-like Paint command sequences, as the methods of the Paint class are designed more for use as a construction description for lines, shapes and text than for free drawing on a suitable drawing area such as a DrawingArea.

The presentation of the projects is supplemented by comments on the specified project source text and numerous images.

Figure 23.3.4.0.1: Tangent array

Source code excerpt:

Public Sub PaintScriptBezierApproximation()
  Dim PS, P1, P2, P3, PE As New PointF
  Dim i, k As Integer
  Dim dx1, dx2, t As Float
 
  GenerateNewPicture()
  SetPictureBorder()  
  Paint.Begin(hPicture) 
    Paint.Translate(xTranslate, yTranslate)
    Paint.Scale(xScale, yScale) '-- +y ▲  
    DrawCoordinateSystem() 
 
    P1.x = 30
    P1.y = 240
    P2.x = 150
    P2.y = 30
    P3.x = 500
    P3.y = 270
    k = 30 '-- Number of tangents
    dx1 = (P2.x - P1.x) / k
    dx2 = (P3.x - P2.x) / k
    ...
    Paint.LineWidth = 1
    For i = 1 To k + 1
      Paint.MoveTo(P1.x + (i - 1) * dx1, a(P1.x + (i - 1) * dx1))
      Paint.LineTo(P2.x + (i - 1) * dx2, b(P2.x + (i - 1) * dx2))    
    Next
    Paint.Stroke()
 
'-- TEXT
    Paint.NewPath
    Paint.Scale(1, -1) '-- ATTENTION: y-axis now with *positive* values downwards!
    Paint.Font = Font["Monospace, 10, bold"]
    Paint.Brush = Paint.Color(Color.Red)
    Paint.DrawText("P1(30|240)", 10, -250)
    Paint.DrawText("P2(150|30)", 120, -10)     
    Paint.DrawText("P3(500|270)", 455, -285)
    Paint.Scale(1, -1)
  Paint.End()
 
End