windows GDI+ 繪圖的簡單封裝

由於用mfc經常需要在界面上進行一些繪製輸出，所以用windows GDI比較多，但是用windowsGDI 繪圖比較麻煩，剛開始學的時候還經常弄不清一堆DC, Object, HANDLE到底是幹啥的。後來就琢磨清楚了，但爲了用起來更方便，就弄個類，這樣畫什麼就直接調對應的函數和常用的控制參數，比如大小位置顏色，而不需要自己去操控上下文、繪製畫筆畫刷等等麻煩事，而且一個函數完成一個簡單圖形的繪製，後面又學了gdi+，就重寫了部分函數實現，用了更簡單的方式完成。

爲了避免閃爍，這裏用了雙緩存的原理，其實就是相當於在內存裏開闢空間畫完後在顯示在屏幕上。至於閃爍的緣由，在我的另一篇博文裏面有淺淺的探究：http://www.straka.cn/blog/flickering-in-mfc/

這裏也不得不指明這麼做是有損效率的，因爲期間會重複創建和銷燬畫筆畫刷等對象。但對於多數應用場景，這個損失是可以接受的。

要使用GDI+（Graphics device interface），要做些鋪墊工作，

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ULONG_PTR m_gdiplusToken;   BOOL CGDIDemoApp::InitInstance() { ... CWinApp::InitInstance();   Gdiplus::GdiplusStartupInput gdiplusStartupInput; Gdiplus::GdiplusStartup(&m_gdiplusToken, &gdiplusStartupInput, NULL); ... }   int CGDIDemoApp::ExitInstance() { // TODO: 在此添加專用代碼和/或調用基類 Gdiplus::GdiplusShutdown(m_gdiplusToken); return CWinApp::ExitInstance(); }

一般爲了方便在應用程序的實例初始化階段就可以把gdiplus一起初始化了，然後實現ExitInstance虛函數，在其中釋放使用gdiplus所佔的資源。

封裝的類：

class CDrawMethod
{
	HWND m_dlgHWND; //the handle of dialog window
	CDC *m_pDC;     //the device context of dialog
	CDC m_dcMem;    //the memory dc, to contain all the drawing than flush onto screen
	CBitmap m_bmpMem;  //bitmap bind to memory dc--m_dcMem 
	Gdiplus::Graphics* m_pGraph; //point to the object of Gdiplus
	
	CDrawMethod(HWND hwnd, CDC *pDC);
	~CDrawMethod();
	//call this func to init the member before any draw method
	int BeginDraw();
	//after all operate has been executed(drawn on memory DC), call this to draw on screen
	void DrawOnScreen();
	//call this func after all operate has done, free or release the resources, in case of memory leak
	int EndDraw();
	
	//save picture in memory DC to path as jpg file
	int SaveMemDCAsJPG(char* strPath);
	int SaveMemDCAsBMP(char* strPath);

	//return the memory bitmap member 
	CBitmap *GetMemBitmap();
	//return the memory DC member
	CDC *GetMemDC();
public:
	CRect m_rtClient;
};

主要的成員和函數都在上述代碼中列出，使用的話每次新建類實例，傳入對話框句柄HANDLE和設備上下文DC，然後調用BeginDraw()初始化，等全部函數執行完畢，再調用DrawOnScreen()畫到屏幕上，最後EndDraw()釋放資源。如果需要更進一步的操作可以用GetMemBitmap() 和 GetMemDC()方法取得內存位圖和畫布進一步操作。但是注意這裏的指針是指向成員的，用完不可釋放，類內部管理。如果畫完不需要顯示在顯示器上也可以用SaveMemDCAsJPG 和 SaveMemDCAsBMP 函數輸出到文件。

而具體承擔繪圖任務的函數是自定義可以添加的：

        //putout the text follow the params onto the dc
TEXTMETRIC PutOutTextA(char* lpsz, int X, int Y, unsigned long lColor, int nFontHeight, int nFontWidth = FW_NORMAL, EShadowType eShadow = NONE, unsigned long lShadowColor = 0, LPCWSTR lpFont = TEXT("微軟雅黑"));
TEXTMETRIC PutOutTextW(char* lpsz, int X, int Y, unsigned long lColor, int nFontHeight, int nFontWidth = FW_NORMAL, EShadowType eShadow = NONE, unsigned long lShadowColor = 0, LPCWSTR lpFont = TEXT("微軟雅黑"));
//draw rectangle frame
void DrawRectFrame(CRect rect,int width, unsigned long lColor,byte alpha=255);
//draw shadow of rectangle
//@param coeff: control the color gradiant rate
void DrawRectShadow(CRect rect, unsigned long lColor, byte alpha, int width, float coeff=0.8);
//fill inside of  rectangle
void FillRect(CRect rect, unsigned long lColor, byte alpha);
void DrawEllipseFrame(CRect rect, int width, unsigned long lColor, byte alpha=255);
void DrawEllipseShadow(CRect rect, unsigned long lColor, byte alpha, int width, float coeff=0.8);
void FillEllipse(CRect rect, unsigned long lColor, byte alpha);
void DrawPolygonFrame(Gdiplus::Point* arrPoints, int ctn, int width, unsigned long lColor, byte alpha=255);
void FillPolygon(Gdiplus::Point* arrPoints, int ctn, unsigned long lColor, byte alpha);
//draw round corner rectangle
void DrawRoundRect(CRect rect, float arcSize, float lineWidth, unsigned long lColor, byte alpha, bool fillPath = false, unsigned long lColorFill = 0, byte alphaFill = 0);
void DrawRoundRect(float x, float y, float Width, float Height, float arcSize, float lineWidth, unsigned long lColor, byte alpha, bool fillPath = false, unsigned long lColorFill = 0, byte alphaFill = 0);
//method to draw cubic of area located by points array
void FillCubicSurface(Gdiplus::Point* arrPoints, int ctn, unsigned long lColor, byte alpha = 155,unsigned long frameColor = 0);
 
//draw image on path by method 1 to location by rect
bool DrawImage(char* pStr, CRect rect);
//draw png picture at path input to location by rect
void DrawPNG(WCHAR* strPath, CRect rect);

我就把常用的一些添加了進來，畫矩形、橢圓形、多邊形框、及填充矩形、橢圓形、多邊形內部、畫矩形、橢圓形陰影，畫圓角矩形、畫立方體，繪製圖片,以及輸出文字。

其中畫矩形陰影實現就是畫了尺寸稍大的多個矩形，這種比較簡單，當然也有別的處理方法，根據大家需要另外添加函數即可。

使用示例：

在對話框OnPaint函數中添加代碼：

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if (IsIconic()) { ...         } else { //CDialogEx::OnPaint(); CPaintDC dc(this); // 用於繪製的設備上下文 CDrawMethod drawMethod(m_hWnd,&dc); drawMethod.BeginDraw(); ...//draw objects here drawMethod.DrawOnScreen();   drawMethod.EndDraw(); }

在第11行處添加畫圖代碼，比如：

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drawMethod.DrawRectFrame(rect1,1,RGB(0,255,0),150); drawMethod.DrawRectShadow(rect1,RGB(200,255,255),200,5); drawMethod.FillRect(rect1,RGB(255,0,0),150);   drawMethod.DrawEllipseFrame(rect2,1,RGB(100,20,155),200); drawMethod.DrawEllipseShadow(rect2,RGB(0,255,255),200,5,0.7); drawMethod.FillEllipse(rect2,RGB(255,255,0),190);   Gdiplus::Point pts[8]; pts[0].X = 170; pts[0].Y = 250; pts[1].X = 280; pts[1].Y = pts[0].Y; pts[2].X = 400; pts[2].Y = 100; pts[3].X = 330; pts[3].Y = pts[2].Y; pts[4].X = pts[0].X; pts[4].Y = 210; pts[5].X = pts[1].X; pts[5].Y = pts[4].Y; pts[6].X = pts[2].X; pts[6].Y = 75; pts[7].X = pts[3].X; pts[7].Y = pts[6].Y; drawMethod.FillCubicSurface(pts,8,RGB(0,200,50),200,RGB(0,255,0));

上述代碼繪圖效果：

Demo源碼等更多信息見原博客：

http://www.straka.cn/blog/encapsulate-gdi-draw-method/