Option Explicit
'ﾘｰｼﾞｮﾝをﾌﾞﾗｼで塗りつぶし
Private Declare Function FillRgn Lib "gdi32" (ByVal hdc As Long, ByVal hRgn As Long, ByVal hBrush As Long) As Long

'色ﾌﾞﾗｼの作成
Private Declare Function CreateSolidBrush Lib "gdi32" (ByVal crColor As Long) As Long

'ｵﾌﾞｼﾞｪｸﾄの削除
Private Declare Function DeleteObject Lib "gdi32" (ByVal hObject As Long) As Long

'多角形ﾘｰｼﾞｮﾝの作成
Private Declare Function CreatePolygonRgn Lib "gdi32" (lpPoint As POINTAPI, ByVal nCount As Long, ByVal nPolyFillMode As Long) As Long

'POINTAPI構造体
Private Type POINTAPI
        X As Long
        Y As Long
End Type

Dim Plg() As POINTAPI, plgCount As Integer

Private Sub Picture1_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single)
    'MouseMoveを呼び出す
    Picture1_MouseMove Button, Shift, X, Y
    
End Sub

Private Sub Picture1_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single)
    
    If Button <> 1 Then Exit Sub 'Buttonが１以外なら入っちゃダメ
    
    Dim BHnd As Long, Rgn
    ReDim Preserve Plg(plgCount) '変動配列の添え字を変える
    
    '現在の位置を保存
    Plg(plgCount).X = X
    Plg(plgCount).Y = Y

    BHnd = CreateSolidBrush(vbBlue) '色ﾌﾞﾗｼを作成
    
    Rgn = CreatePolygonRgn(Plg(0), plgCount, 1) '多角形のﾘｰｼﾞｮﾝを作成
    
    Call FillRgn(Picture1.hdc, Rgn, BHnd) 'ﾘｰｼﾞｮﾝを塗りつぶし
    
    Call DeleteObject(BHnd) '色ﾌﾞﾗｼを削除
    Call DeleteObject(Rgn) 'ﾘｰｼﾞｮﾝを削除
    Picture1.Refresh '表示
    plgCount = plgCount + 1 '配列の最大添え字数を増やす
End Sub