Wyo VB Lecture Notes

Objective #1: Use collision detection to control animation.

• Collision detection is code that responds to graphics when they touch each other or a boundary of the form.
  
  
• The following code could also be used to detect a collision by checking to see if the picPlayer object collides with a horizontal line that has endpoints of (30, 20) and (100, 20).
    
     If (picPlayer.Top < 20 And picPlayer.Bottom > 20 And picPlayer.Right > 30 And picPlayer.Left < 100) Then
           MessageBox.Show("Collision Occurred")
     End If
  
  Note that unlike Top, Bottom is a "read only" property of a PictureBox, so it can be used in If statements like the one above but it cannot be used in an assignment statement like picCircle.Bottom = 100
  
  Similarly, Right is a "read only" property.
  
  
• The following code could also be used to detect a collision by checking to see if the picPlayer object collides with a vertical line that has endpoints of (100, 20) and (100, 150).
    
      If (picPlayer.Right > 100 And picPlayer.Left < 100 And picPlayer.Bottom > 20 And picPlayer.Top < 150) Then
           MessageBox.Show("Collision Occurred")
     End If
  
  
• The following code could also be used to detect a collision with a diagonal lines
  
  

      ' lines must be defined with the x1, y1 point being the leftmost endpoint
      ' and the x2, y2 point being the rightmost endpoint
  
      ' line 1 slanted down from left to right
      Dim l1x1 As Integer = 100
      Dim l1y1 As Integer = 20
      Dim l1x2 As Integer = 200
      Dim l1y2 As Integer = 200
      Dim m1 As Double = (l1y2 - l1y1) / (l1x2 - l1x1)
  
      ' line 2 slanted up from left to right
      Dim l2x1 As Integer = 10
      Dim l2y1 As Integer = 300
      Dim l2x2 As Integer = 200
      Dim l2y2 As Integer = 200
      Dim m2 As Double = (l2y2 - l2y1) / (l2x2 - l2x1)
  
      e.Graphics.DrawLine(New Pen(Color.Black, 1), l1x1, l1y1, l1x2, l1y2)
      e.Graphics.DrawLine(New Pen(Color.Black, 1), l2x1, l2y1, l2x2, l2y2)
  
  
      ' line 1
      If (picPlayer.Bottom > l1y1 And picPlayer.Top < l1y2 And picPlayer.Right > l1x1 And picPlayer.Left < l1x2 And picPlayer.Top < m1 * (picPlayer.Right - l1x1) + l1y1 And picPlayer.Bottom > m1 * (picPlayer.Left - l1x1) + l1y1) Then
              MessageBox.Show("hit line 1")
      End If
  
       ' line 2
       If (picPlayer.Bottom > l2y2 And picPlayer.Top < l2y1 And picPlayer.Right > l2x1 And picPlayer.Left < l2x2 And picPlayer.Top < m2 * (picPlayer.Left - l2x1) + l2y1 And picPlayer.Bottom > m2 * (picPlayer.Right - l2x1) + l2y1) Then
              MessageBox.Show("hit line 2")
       End If