Method DrawGradient

DuiLib/Core/UIRender.cpp:1082–1156

}

void CRenderEngine::DrawGradient(HDC hDC, const RECT& rc, DWORD dwFirst, DWORD dwSecond, bool bVertical, int nSteps)
{
    typedef BOOL (WINAPI *LPALPHABLEND)(HDC, int, int, int, int,HDC, int, int, int, int, BLENDFUNCTION);
    static LPALPHABLEND lpAlphaBlend = (LPALPHABLEND) ::GetProcAddress(::GetModuleHandle(_T("msimg32.dll")), "AlphaBlend");
    if( lpAlphaBlend == NULL ) lpAlphaBlend = AlphaBitBlt;
    typedef BOOL (WINAPI *PGradientFill)(HDC, PTRIVERTEX, ULONG, PVOID, ULONG, ULONG);
    static PGradientFill lpGradientFill = (PGradientFill) ::GetProcAddress(::GetModuleHandle(_T("msimg32.dll")), "GradientFill");

    BYTE bAlpha = (BYTE)(((dwFirst >> 24) + (dwSecond >> 24)) >> 1);
    if( bAlpha == 0 ) return;
    int cx = rc.right - rc.left;
    int cy = rc.bottom - rc.top;
    RECT rcPaint = rc;
    HDC hPaintDC = hDC;
    HBITMAP hPaintBitmap = NULL;
    HBITMAP hOldPaintBitmap = NULL;
    if( bAlpha < 255 ) {
        rcPaint.left = rcPaint.top = 0;
        rcPaint.right = cx;
        rcPaint.bottom = cy;
        hPaintDC = ::CreateCompatibleDC(hDC);
        hPaintBitmap = ::CreateCompatibleBitmap(hDC, cx, cy);
        ASSERT(hPaintDC);
        ASSERT(hPaintBitmap);
        hOldPaintBitmap = (HBITMAP) ::SelectObject(hPaintDC, hPaintBitmap);
    }
    if( lpGradientFill != NULL ) 
    {
        TRIVERTEX triv[2] = 
        {
            { rcPaint.left, rcPaint.top, GetBValue(dwFirst) << 8, GetGValue(dwFirst) << 8, GetRValue(dwFirst) << 8, 0xFF00 },
            { rcPaint.right, rcPaint.bottom, GetBValue(dwSecond) << 8, GetGValue(dwSecond) << 8, GetRValue(dwSecond) << 8, 0xFF00 }
        };
        GRADIENT_RECT grc = { 0, 1 };
        lpGradientFill(hPaintDC, triv, 2, &grc, 1, bVertical ? GRADIENT_FILL_RECT_V : GRADIENT_FILL_RECT_H);
    }
    else 
    {
        // Determine how many shades
        int nShift = 1;
        if( nSteps >= 64 ) nShift = 6;
        else if( nSteps >= 32 ) nShift = 5;
        else if( nSteps >= 16 ) nShift = 4;
        else if( nSteps >= 8 ) nShift = 3;
        else if( nSteps >= 4 ) nShift = 2;
        int nLines = 1 << nShift;
        for( int i = 0; i < nLines; i++ ) {
            // Do a little alpha blending
            BYTE bR = (BYTE) ((GetBValue(dwSecond) * (nLines - i) + GetBValue(dwFirst) * i) >> nShift);
            BYTE bG = (BYTE) ((GetGValue(dwSecond) * (nLines - i) + GetGValue(dwFirst) * i) >> nShift);
            BYTE bB = (BYTE) ((GetRValue(dwSecond) * (nLines - i) + GetRValue(dwFirst) * i) >> nShift);
            // ... then paint with the resulting color
            HBRUSH hBrush = ::CreateSolidBrush(RGB(bR,bG,bB));
            RECT r2 = rcPaint;
            if( bVertical ) {
                r2.bottom = rc.bottom - ((i * (rc.bottom - rc.top)) >> nShift);
                r2.top = rc.bottom - (((i + 1) * (rc.bottom - rc.top)) >> nShift);
                if( (r2.bottom - r2.top) > 0 ) ::FillRect(hDC, &r2, hBrush);