Symbian绘制渐变矩形的两种方法

 第一种方法（推荐）：

这是我参考其它语言修改成Symbian版本的，使用方法很简单，直接调用DrawShadeRect方法就可以绘制渐变的矩形了。

这种方法原理其实也很简单，感兴趣的可以看看 TransitionalColor这个方法。

static void GetRGBFromHex(TUint aColor,TInt &aRed,TInt &aGreen,TInt &aBlue)  

{  

    aRed    = (aColor & 0xff0000) >> 16;

    aGreen  = (aColor & 0x00ff00) >> 8;  

    aBlue   = (aColor & 0x0000ff);  

}



static void GetHexFromRGB(TUint &aColor,TInt aRed,TInt aGreen,TInt aBlue)  

{  

    if(aRed < 0 || aRed > 255 || aGreen < 0 || aGreen > 255 || aBlue < 0 || aBlue > 255)

    {

        aColor = 0xFFFFFF;

    }



    aColor =  aRed << 16 | aGreen << 8 | aBlue;  

}  



/** 

 * color1是浅色,color2是深色,实现渐变 

 * steps是指在多大的区域中渐变, 

 */  

static RArray<TUint> TransitionalColor(TUint aColor1,TUint aColor2,TInt steps)  

{

    RArray<TUint> array;



    if(steps < 3)  

        return array;



    TInt R1,G1,B1,R2,G2,B2;

    GetRGBFromHex(aColor1,R1,G1,B1);

    GetRGBFromHex(aColor2,R2,G2,B2);



    array.AppendL(aColor1);

    steps = steps - 2;  



    TInt redDiff    = R2 - R1;  

    TInt greenDiff  = G2 - G1;  

    TInt blueDiff   = B2 - B1;  

    for(TInt i = 1; i < steps + 1; i++)  

    {

        TUint c;

        GetHexFromRGB(c,

                R1 + redDiff * i / steps,  

                G1 + greenDiff * i / steps,  

                B1 + blueDiff * i / steps  

                );

        array.AppendL(c);

    }  



    array.AppendL(aColor2);

    return array;  

}  



/*

 * 绘制渐变矩形

 * */

static void DrawShadeRect(CWindowGc& aGc,TRect aRect,TUint aBeginColor,TUint aEndColor)

{

    aGc.SetPenStyle(CGraphicsContext::ESolidPen);



    TInt height = aRect.Height();

    RArray<TUint> colors = TransitionalColor(aBeginColor,aEndColor,height);



    TInt count = colors.Count();

    for (TInt i = 0;i < height;i++)

    {

        TRgb penColor(colors[i]);

        aGc.SetPenColor(penColor);

        aGc.DrawLine(TPoint(0,i),TPoint(aRect.Width(),i));

    }

    colors.Close();

}

另外绘制渐变渐变矩形还有下面这种方法，但是这种方法效率比较低下，而且效果也不是很理想，建议使用上面直接画线的方法。

第二种方法： 

CFbsBitmap* brush=new(ELeave)CFbsBitmap;
TRgb startColor=KRgbBlue;
TRgb endColor=KRgbWhite; 
TInt brushWidth=10;
ColorUtils::TBitmapOrientation brushOrientation=ColorUtils::EBitmapOrientationVertical;
ColorUtils::CreateGradientBitmapL(*brush, CEikonEnv::Static()->WsSession(), brushWidth, brushOrientation, startColor, endColor);
// bitmap->SetDisplayMode(EColor64K); 如果真机上无法显示，应加上这句代码
gc.DrawBitmap(TRect(aRect.iTl.iX, aRect.iTl.iY, aRect.iBr.iX, aRect.iBr.iY), bitmap);
delete brush;
brush = NULL;