GDI 区域检测与边框宽度的关系

GDI32中用PtInRegion检测坐标是否在图形区域内： 如果画了一个矩形,外边框线条粗细是10像素,检测区域时只能在第6像素开始才能反应,鼠标移动到边框线的1-5像素时,检测鼠标未在矩形区域

您遇到的问题是由于 GDI 中区域 (Region) 的定义与边框 (Stroke) 的渲染方式不同导致的。这是 GDI 绘图系统的一个常见特性，需要特别处理。

问题原因分析

1. 区域 (Region) vs 边框 (Stroke)

   • CreateRectRgn 创建的区域是填充区域，不包含边框
   • 边框是绘制在区域边缘外部的，默认情况下不被视为区域的一部分

2. 边框宽度的影响

   • 当您设置边框宽度为 10 像素时，这 10 像素是从区域边缘向外扩展的
   • 区域本身的边界并没有改变，因此PtInRegion只检测填充区域

3. 坐标系统差异

   • 区域使用整数坐标，而边框渲染可能使用亚像素精度
   • 这种差异可能导致视觉上的边框与实际区域边界不一致

解决方案

方法一：创建包含边框的扩展区域vb

' API声明
Private Declare Function CreateRectRgn Lib "gdi32" (ByVal X1 As Long, ByVal Y1 As Long, ByVal X2 As Long, ByVal Y2 As Long) As Long
Private Declare Function CombineRgn Lib "gdi32" (ByVal hDestRgn As Long, ByVal hSrcRgn1 As Long, ByVal hSrcRgn2 As Long, ByVal nCombineMode As Long) As Long
Private Declare Function PtInRegion Lib "gdi32" (ByVal hRgn As Long, ByVal x As Long, ByVal y As Long) As Long
Private Declare Function DeleteObject Lib "gdi32" (ByVal hObject As Long) As Long

Private Const RGN_OR = 2  ' 区域合并操作

Private Sub CreateExtendedRegion(ByVal left As Long, ByVal top As Long, ByVal right As Long, ByVal bottom As Long, ByVal borderWidth As Long, ByRef hRegion As Long)
    Dim hFillRgn As Long
    Dim hBorderRgn As Long
    
    ' 创建填充区域
    hFillRgn = CreateRectRgn(left, top, right, bottom)
    
    ' 创建扩展区域（包含边框）
    hBorderRgn = CreateRectRgn(left - borderWidth, top - borderWidth, _
                              right + borderWidth, bottom + borderWidth)
    
    ' 合并两个区域
    hRegion = CreateRectRgn(0, 0, 1, 1)  ' 创建临时区域
    CombineRgn hRegion, hFillRgn, hBorderRgn, RGN_OR
    
    ' 释放临时区域
    DeleteObject hFillRgn
    DeleteObject hBorderRgn
End Sub

' 使用示例
Private Sub Form_Load()
    Dim hRegion As Long
    Dim borderWidth As Long
    
    borderWidth = 10
    
    ' 创建包含10像素边框的区域
    CreateExtendedRegion 100, 100, 300, 200, borderWidth, hRegion
    
    ' 现在可以使用这个区域进行鼠标检测
    ' PtInRegion(hRegion, x, y) 将包含边框区域
End Sub

方法二：分别检测填充区域和边框区域vb

Private Sub MouseInBorderOrFill(ByVal x As Long, ByVal y As Long, ByVal left As Long, ByVal top As Long, ByVal right As Long, ByVal bottom As Long, ByVal borderWidth As Long, ByRef inBorder As Boolean, ByRef inFill As Boolean)
    ' 检测是否在填充区域内
    inFill = (x >= left And x <= right And y >= top And y <= bottom)
    
    ' 检测是否在边框区域内
    If Not inFill Then
        inBorder = (x >= left - borderWidth And x <= right + borderWidth And _
                   y >= top - borderWidth And y <= bottom + borderWidth) And _
                  Not inFill
    Else
        inBorder = False
    End If
End Sub

' 使用示例
Private Sub Form_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single)
    Dim pixelX As Long, pixelY As Long
    Dim inBorder As Boolean, inFill As Boolean
    
    pixelX = X / Screen.TwipsPerPixelX
    pixelY = Y / Screen.TwipsPerPixelY
    
    ' 检测鼠标是否在矩形(100,100,300,200)的填充区域或边框(宽度10)内
    MouseInBorderOrFill pixelX, pixelY, 100, 100, 300, 200, 10, inBorder, inFill
    
    If inFill Then
        Me.Caption = "鼠标在填充区域内"
    ElseIf inBorder Then
        Me.Caption = "鼠标在边框区域内"
    Else
        Me.Caption = "鼠标在区域外"
    End If
End Sub

方法三：使用 GDI + 进行精确检测

GDI + 提供了更精确的区域检测功能，可以直接包含边框：

' GDI+ API声明
Private Declare Function GdipCreateFromHDC Lib "gdiplus" (ByVal hdc As Long, ByRef graphics As Long) As Long
Private Declare Function GdipDeleteGraphics Lib "gdiplus" (ByVal graphics As Long) As Long
Private Declare Function GdipCreatePen1 Lib "gdiplus" (ByVal color As Long, ByVal width As Single, ByVal unit As Long, ByRef pen As Long) As Long
Private Declare Function GdipCreatePath Lib "gdiplus" (ByVal fillMode As Long, ByRef path As Long) As Long
Private Declare Function GdipAddPathRectangle Lib "gdiplus" (ByVal path As Long, ByVal x As Single, ByVal y As Single, ByVal width As Single, ByVal height As Single) As Long
Private Declare Function GdipIsVisiblePathPoint Lib "gdiplus" (ByVal x As Single, ByVal y As Single, ByVal path As Long, ByVal pen As Long, ByVal graphics As Long) As Long
Private Declare Function GdipDisposePath Lib "gdiplus" (ByVal path As Long) As Long
Private Declare Function GdipDisposePen Lib "gdiplus" (ByVal pen As Long) As Long

Private Const UnitPixel As Long = 2

Private Sub Form_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single)
    Dim pixelX As Single, pixelY As Single
    Dim hGraphics As Long
    Dim hPath As Long
    Dim hPen As Long
    Dim isVisible As Long
    
    pixelX = X / Screen.TwipsPerPixelX
    pixelY = Y / Screen.TwipsPerPixelY
    
    ' 创建GDI+图形对象
    GdipCreateFromHDC Me.hdc, hGraphics
    
    ' 创建路径和笔
    GdipCreatePath 0, hPath  ' 0 = FillModeAlternate
    GdipCreatePen1 &HFF0000, 10, UnitPixel, hPen  ' 10像素宽的笔
    
    ' 添加矩形到路径
    GdipAddPathRectangle hPath, 100, 100, 200, 100
    
    ' 检测点是否在路径(包括边框)上
    isVisible = GdipIsVisiblePathPoint(pixelX, pixelY, hPath, hPen, hGraphics)
    
    If isVisible <> 0 Then
        Me.Caption = "鼠标在矩形(包括边框)内"
    Else
        Me.Caption = "鼠标在矩形外"
    End If
    
    ' 释放资源
    GdipDisposePath hPath
    GdipDisposePen hPen
    GdipDeleteGraphics hGraphics
End Sub

性能考虑

1. 扩展区域方法：性能较高，但需要额外管理区域对象
2. 分别检测方法：简单直接，适合小型应用
3. GDI + 方法：最精确，但性能开销较大，适合对精度要求高的场景

根据您的具体需求选择合适的方法，可以有效解决边框检测问题。