Thread: VB.NET - Drawing Lines From Scratch (Bresenham)

1. VB.NET - Drawing Lines From Scratch (Bresenham)

Howdy fellow programmers,

Learning to draw lines on a computer screen is part of the basic useful stuff.
Reinventing the wheel being my main focus I looked around to find out how, but most if not all documents on the subject are pure algebra or implemented in languages that may differ from VB.NET.

Therefore I made my own implementation of Bresenham's Algorithm in VB.NET to give a general idea of the concept at hand to those freaked out by algebra lectures.

PS: This is not yet fully optimized speed wise but unless you do very heavy 3D computations the difference with a more optimized version won't be visible.
The code is presented raw, I'll eventually update this post with a properly commented version.

vb.net Code:
```Private Sub DrawLine(ByVal Canvas As Bitmap, ByVal X0 As Integer, ByVal Y0 As Integer, ByVal X1 As Integer, ByVal Y1 As Integer)
If X0 > X1 Then
Dim Tx As Integer = X0
Dim Ty As Integer = Y0
X0 = X1 : Y0 = Y1
X1 = Tx : Y1 = Ty
End If
Dim Delta_X As Integer = X1 - X0
Dim Delta_Y As Integer = Y1 - Y0
If Delta_X = 0 And Delta_Y = 0 Then
Canvas.SetPixel(X0, Y0, Color.Black)
ElseIf Delta_X = 0 Then
If Delta_Y > 0 Then
For I = Y0 To Y1
Canvas.SetPixel(X0, I, Color.Black)
Next
ElseIf Delta_Y < 0 Then
For I = Y1 To Y0
Canvas.SetPixel(X0, I, Color.Black)
Next
End If
ElseIf Delta_Y = 0 Then
If Delta_X > 0 Then
For I = X0 To X1
Canvas.SetPixel(I, Y0, Color.Black)
Next
ElseIf Delta_X < 0 Then
For I = X1 To X0
Canvas.SetPixel(I, Y0, Color.Black)
Next
End If
Else
If Math.Abs(Delta_Y) > Math.Abs(Delta_X) Then
Dim Delta_Err As Single = (Delta_X / Delta_Y)
Dim Err As Single = 0
If Delta_Err > 0 Then
Dim X_Value As Integer = X0
For I = Y0 To Y1
Canvas.SetPixel(X_Value, I, Color.Black)
Err += Delta_Err
If Err > 0.5 Then
X_Value += 1
Err -= 1
End If
Next
Else
Dim X_Value As Integer = X1
For I = Y1 To Y0
Canvas.SetPixel(X_Value, I, Color.Black)
Err += Delta_Err
If Err < -0.5 Then
X_Value -= 1
Err += 1
End If
Next
End If
Else
Dim Delta_Err As Single = Delta_Y / Delta_X
Dim Err As Single = 0
If Delta_Err > 0 Then
Dim Y_Value As Integer = Y0
For I = X0 To X1
Canvas.SetPixel(I, Y_Value, Color.Black)
Err += Delta_Err
If Err > 0.5 Then
Y_Value += 1
Err -= 1
End If
Next
Else
Dim Y_Value As Integer = Y0
For I = X0 To X1
Canvas.SetPixel(I, Y_Value, Color.Black)
Err += Delta_Err
If Err < -0.5 Then
Y_Value -= 1
Err += 1
End If
Next
End If
End If
End If
End Sub```

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