在内存中画图实现双缓冲

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在C++builder中防止画图闪烁，一般需要用到双缓冲，即在内存中画图，然后复制到界面上去。

.h文件如下：

class TForm1 : public TForm{   __published:// IDE-managed Components        TTimer *Timer1;        TImage *Image1;        void __fastcall Timer1Timer(TObject *Sender);   private:// User declarations            ULONG_PTR   GdiplusToken;   //GDI初始化相关            Gdiplus::GdiplusStartupInput   GdiplusStartupInput;   public:// User declarations        __fastcall TForm1(TComponent* Owner);        __fastcall   ~TForm1(void);        HDC m_hdcMemory;  //内存句柄        HDC hdcTemp;      //设备上下文句柄        HBITMAP hBitMap;  //位图句柄};//---------------------------------------------------------------------------extern PACKAGE TForm1 *Form1;

.cpp文件中调用GDI+画图，代码如下：

#include <vcl.h>#pragma hdrstop#include   <math.h>   #include   <algorithm>using      std::min;using      std::max;#include   "gdiplus.h"using   namespace   Gdiplus;#include "Unit1.h"//---------------------------------------------------------------------------#pragma package(smart_init)#pragma resource "*.dfm"TForm1 *Form1;#pragma   warn   -inl#pragma   warn   -8022Gdiplus::Graphics *g;//---------------------------------------------------------------------------__fastcall TForm1::TForm1(TComponent* Owner)        : TForm(Owner){        Image1->Parent->DoubleBuffered = true;        GdiplusStartup(&GdiplusToken,   &GdiplusStartupInput,   NULL);   //初始化GDI+                //---------------------------------------        hdcTemp = GetDC(0);//设备上下文环境句柄        m_hdcMemory = CreateCompatibleDC(hdcTemp);//内存环境句柄        hBitMap = CreateCompatibleBitmap(hdcTemp,450,265);//该函数创建与指定的设备环境相关的设备兼容的位图        SelectObject(m_hdcMemory, hBitMap);//该函数选择一对象到指定的设备上下文环境中        g= new Gdiplus::Graphics(m_hdcMemory);        }//---------------------------------------------------------------------------__fastcall  TForm1::~TForm1(void)   {        GdiplusShutdown(GdiplusToken);   //   关闭GDI+        ReleaseDC(0, hdcTemp);        hdcTemp = NULL;        DeleteObject(hBitMap);        DeleteDC(m_hdcMemory);        m_hdcMemory = NULL;}//---------------------------------------------------------------------------void __fastcall TForm1::Timer1Timer(TObject *Sender){        const static int OX = 200, OY = 200;const static REAL C = 140;const static REAL PI = 3.14;static REAL offset = 0;POINT p[4];REAL k[4];        //==============================// 生成正文形四角的新坐标值for (int i=0; i < 4; i++){   k[i] = offset + (PI / 2) * i;           p[i].x = (int)OX + C*sin(k[i]);           p[i].y = (int)OY + C*cos(k[i]);}g->SetSmoothingMode(SmoothingModeHighQuality); //高画质、低速// 重新填充背景SolidBrush brush(Color::Color(100,0,0));//画刷Pen pen(Color::Color(255, 0, 0), 1);//画笔g->FillRectangle(&brush, 0, 0, ClientWidth, ClientHeight); //画矩形Gdiplus::Point point1(p[0].x, p[0].y);//设置点坐标Gdiplus::Point point2(p[1].x, p[1].y);Gdiplus::Point point3(p[2].x, p[2].y);Gdiplus::Point point4(p[3].x, p[3].y);Gdiplus::Point point5(p[0].x, p[0].y);// 在新坐标绘画正方形Gdiplus::Point points[] = {point1, point2, point3, point4, point5};g->DrawLines(&pen, points, 5);//画线offset += 0.1;                BitBlt(Image1->Canvas->Handle, 0, 0, 600, 600, m_hdcMemory, 0, 0, SRCCOPY);//复制内存中的图像到界面上去        Image1->Repaint();}

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