上一个帖子的解决方案：
Option Explicit
Private Declare Function ExtFloodFill Lib "gdi32" (ByVal hdc As Long, ByVal X As Long, ByVal Y As Long, ByVal crColor As Long, ByVal wFillType As Long) As Long
Dim X0, Y0 As Double
Dim X(1 To 5), Y(1 To 5) As Double
Dim Xtop0, Ytop0, Xbot0, Ybot0 As Double
Private Sub tianchong()
    Dim i As Integer
    Dim Xhalf, Yhalf As Double
    Dim Kx, Ky As Double
    Dim Xpixel(1 To 5), Ypixel(1 To 5) As Double
   
    Picture1.ScaleMode = 3
    Picture1.AutoRedraw = True
    Picture1.ForeColor = vbRed
    Picture1.FillColor = vbBlack
    Picture1.FillStyle = 0
   
    Kx = Picture1.Width / (Xbot0 - Xtop0)
    Ky = Picture1.Height / (Ybot0 - Ytop0)
   
    Xpixel(1) = Kx * X(1): Ypixel(1) = Ky * Y(1)
    Xpixel(2) = Kx * X(2): Ypixel(2) = Ky * Y(2)
    Xpixel(3) = Kx * X(3): Ypixel(3) = Ky * Y(3)
    Xpixel(4) = Kx * X(4): Ypixel(4) = Ky * Y(4)
    Xpixel(5) = Kx * X(5): Ypixel(5) = Ky * Y(5)
   
'    For i = 1 To 5
'        MsgBox Xpixel(i): MsgBox Ypixel(i)
'    Next i
'    MsgBox Picture1.Width: MsgBox Picture1.Height
   
    Picture1.Line (Xpixel(1), Ypixel(1))-(Xpixel(2), Ypixel(2))
    Picture1.Line -(Xpixel(3), Ypixel(3))
    Picture1.Line -(Xpixel(4), Ypixel(4))
    Picture1.Line -(Xpixel(5), Ypixel(5))
    Picture1.Line -(Xpixel(1), Ypixel(1))
'
    X0 = (Xpixel(1) + Xpixel(2) + Xpixel(3) + Xpixel(4) + Xpixel(5)) / 5
    Y0 = (Ypixel(1) + Ypixel(2) + Ypixel(3) + Ypixel(4) + Ypixel(5)) / 5
    MsgBox X0: MsgBox Y0
    Call ExtFloodFill(Picture1.hdc, X0, Y0, vbRed, 0)
   
End Sub

Private Sub Form_Load()
    Xtop0 = 0: Ytop0 = 0
    Xbot0 = 100: Ybot0 = 100
    Form1.ScaleMode = 3
    X(1) = 20: Y(1) = 20
    X(2) = 40: Y(2) = 20
    X(3) = 60: Y(3) = 30
    X(4) = 40: Y(4) = 40
    X(5) = 20: Y(5) = 40
    Call tianchong
    Picture1.Scale (Xtop0, Ytop0)-(Xbot0, Ybot0)
    Picture1.Line (40, 40)-(50, 50), RGB(255, 0, 0)
End Sub