PRB: Value of the Point Function Does Not Match Set Color (190180)

SYMPTOMS

When using the Visual Basic Point function to determine the color of the specified point, the RGB color value returned does not always match the region's color as set by the developer at design-time. Consequently, direct comparisons between a given point's color and a color property setting should be avoided because the values may not always agree.

CAUSE

This problem is typically the result of one of the following situations:

The developer has set the color value for a property to a system color (such as., &H80000001) instead of a valid RGB color value. The Point method will always return an RGB value.
The color value has been set to a color that is not within the range of valid colors for the video hardware (or display settings) on an end user's system. Such colors are typically translated to the nearest matching color based on the available system palette. This means that you can never guarantee that the Point function will exactly match the developer's chosen design-time color value.

RESOLUTION

The only way to guarantee that a value returned from the Point function is the color setting chosen by the developer is to set a variable at run-time to a known point that contains the correct color, and use this value during comparisons. For example, if you know that coordinate 100,100 always contains the FillColor then you can set a variable to Point(100,100), and then use this variable when comparing a given point's color to the FillColor, as follows:

   ActualFillColor = Point(100, 100)
   If ActualFillColor = Point(x, y) Then
      ' Do some code ...
   End If

MORE INFORMATION

Steps to Reproduce Behavior

Start a new Standard EXE project in Visual Basic. Form1 is created by default.
Add a Label, Label1, and a Shape control, Shape1, to Form1.

Add the following code to Form1's module:

      Private Sub Form_Load()
         Label1.Caption = "Test Color"
         Shape1.FillStyle = 0 'Solid
         Shape1.FillColor = &H8000000D 'System Color
      End Sub

      Private Sub Form_MouseMove(Button As Integer, Shift As Integer, _
                                 X As Single, Y As Single)
         Dim Color As Long
         Color = Me.Point(X, Y)
         If Color = Shape1.FillColor Then
            Label1.Caption = "Mouse is over the shape!"
         Else
            Label1.Caption = "Mouse is Not over the shape!"
         End If
      End Sub

Run the program by hitting the F5 key or choosing Start from the Run menu. Move the mouse over the form. Note that the label never indicates that the mouse is over the shape. To correct the problem, you need to compare the MouseMove point value to a known point value.

Stop the project and replace Form1's MouseMove event with this code:

      Private Sub Form_MouseMove(Button As Integer, Shift As Integer, _
                                 X As Single, Y As Single)
         Dim ActualFillColor As Long
         Dim Color As Long
         ActualFillColor = Me.Point(Shape1.Left + 10, Shape1.Top + 10)
         Color = Me.Point(X, Y)
         If Color = ActualFillColor Then
            Label1.Caption = "Mouse is over the shape!"
         Else
            Label1.Caption = "Mouse is Not over the shape!"
         End If
      End Sub

Run the program by pressing the F5 key. Note that now when you move the mouse over the form, the label correctly shows when the mouse is over the shape.