Bug Proofing Visual Basic: A Guide to Error Handling and Prevention
(Publisher: John Wiley & Sons, Inc.)
Author(s): Rod Stephens
ISBN: 0471323519
Publication Date: 11/01/98

Note that the background is smoothly shaded only on computers using high color graphics. If your computer is using 256 color mode, the background will be covered with large bands of color. It will still have the same bad performance, however.

Examine the code and figure out where it is spending all of its time. Use the Visual Basic Code Profiler (VBCP) if you like, or look at the timing results shown in Table 16.1. Then modify the code to improve the program’s performance without introducing other bugs.

Figure 16.1  Program Bad16 displaying a bar chart.

Option Explicit

Private Values(1 To 10) As Single

‘ Generate some random data and draw the graph.
Private Sub Form_Load()
   ‘ Load some random data.    
    LoadData    

   ‘ Shade the background.    
    ShadePicture
    
   ‘ Draw the graph.    
    DrawGraph
End Sub

   ‘ Create some random data.
   Private Sub LoadData()
   Dim i As Integer
   Dim min As Single
   Dim max As Single    
     
       Randomize    
     
       min = picGraph.ScaleHeight * 0.1    
       max = picGraph.ScaleHeight * 0.8    
       For i = 1 To 10        
              Values(i) = Int((max - min + 1) * Rnd + min)    
       Next i
   End Sub
     
   ‘ Shade picGraph from white at the top to
    ‘ black at the bottom.
    Private Sub ShadePicture()
    Const START_COLOR = 255
    Const END_COLOR = 0
    Dim Y As Single
    Dim clr As Single
    Dim d_clr As Single    
   
        d_clr = (END_COLOR - START_COLOR) / picGraph.ScaleHeight          clr = START_COLOR    
        For Y = 0 To picGraph.ScaleHeight        
            picGraph.Line (0, Y)- _            
                (picGraph.ScaleWidth, Y), _            
                RGB(clr, clr, clr)        
            clr = clr + d_clr    
        Next Y
    End Sub
     
   ‘ Draw the graph.
   Private Sub DrawGraph()
   Dim i As Integer
   Dim dx As Single
   Dim y0 As Single    
    
       y0 = picGraph.ScaleHeight * 0.9    
       dx = picGraph.ScaleWidth / 12
    
       ‘ Draw the bar chart.    
        For i = 1 To 10        
            picGraph.Line (i * dx, y0)-((i + 1) * dx, Values(i)), vbRed, BF    
        Next i    
        For i = 1 To 10        
            picGraph.Line (i * dx, y0)-((i + 1) * dx, Values(i)), vbBlack, B    
        Next i
    End Sub