快速對圖片進行濾光處理

想快速地對指定圖片或地區進行濾光處理，常見的方法取出圖片資料，逐像素與指定濾光色進行AND運算，很麻煩。還見過網上流傳的有用Point或GetPixel取點運算的，其低速可想而知。

其實利用BitBlt的位元運算，可高速完成這種操作，下面這個函數比數組運算方法可快10倍，比Point或GetPixel估計會快上千倍。

Private Type RECT
        Left As Long
        Top As Long
        Right As Long
        Bottom As Long
End Type
Private Declare Function DeleteObject Lib "gdi32" (ByVal hObject As Long) As Long
Private Declare Function CreateSolidBrush Lib "gdi32.dll" (ByVal crColor As Long) As Long
Private Declare Function FillRect Lib "user32.dll" (ByVal hdc As Long, lpRect As RECT, ByVal hBrush As Long) As Long
Private Declare Function BitBlt Lib "gdi32" (ByVal hDestDC As Long, ByVal X As Long, ByVal y As Long, ByVal nWidth As Long, ByVal nHeight As Long, ByVal hSrcDC As Long, ByVal xSrc As Long, ByVal ySrc As Long, ByVal dwRop As Long) As Long

Public Sub FilterRGB(dHdc As Long, X As Long, y As Long, w As Long, h As Long, Optional tc As Long = &HFFFF00)
    Dim tmphdc As MemHdc, rc As RECT, hBrush As Long
    tmphdc = NewMyHdc(dHdc, w, h)   '建立一個記憶體位元影像
    rc.Right = w
    rc.Bottom = h
    hBrush = CreateSolidBrush(tc)
    FillRect tmphdc.hdc, rc, hBrush '用濾光色填充圖片,產生一個純色圖片
    DeleteObject hBrush
    BitBlt dHdc, X, y, w, h, tmphdc.hdc, 0, 0, vbSrcAnd   '繪入目標，並與目標進行And運算，達到濾光效果
    tmphdc = DelMyHdc(tmphdc)
End Sub

本篇中的公用函數NewMyHdc、DelMyHdc及相關結構與API聲明，可在以下文章中找到
http://blog.csdn.net/homezj/archive/2005/04/14/348001.aspx