GDI+在内存中绘图

为了防止画图闪烁，一般先将图像画制到内存中，再复制到界面上去。C++builder中的控件或窗体本身有双缓冲功能，即本身具有这种功能。但是对于GDI+来说，并没有封装成到TCanvas类中。因此用GDI+来绘图时，会存在闪烁的现象，那么可以用内存绘图来解决。

简单的内存绘图类如下：

#ifndef __BCBMEN__#define __BCBMEM__#include   <math.h>   #include   <algorithm>using   std::min;using   std::max;#include   "gdiplus.h"#pragma   warn   -inl#pragma   warn   -8022using   namespace   Gdiplus;class MemCanvas{   private:        HDC m_hdcMemory;  //内存句柄        HDC hdcTemp;      //设备上下文句柄        HBITMAP hBitMap;  //位图句柄        TSize m_size;   public:        HDC __fastcall CreateMemCanvas(int width,int height);        __fastcall ~MemCanvas();        void __fastcall CanvasCopy(TCanvas * Img,TRect rc,int left,int top,int mode);};HDC __fastcall MemCanvas::CreateMemCanvas(int width,int height){    //==============================    hdcTemp = GetDC(0);//设备上下文环境句柄    m_hdcMemory = CreateCompatibleDC(hdcTemp);//内存环境句柄    //该函数创建与指定的设备环境相关的设备兼容的位图    hBitMap = CreateCompatibleBitmap(hdcTemp,width,height);    SelectObject(m_hdcMemory, hBitMap);//该函数选择一对象到指定的设备上下文环境中    return m_hdcMemory;}__fastcall MemCanvas::~MemCanvas(){    ReleaseDC(0, hdcTemp);    hdcTemp = NULL;    DeleteObject(hBitMap);    DeleteDC(m_hdcMemory);    m_hdcMemory = NULL;}

//复制到指定TCanvas中，mode = SRCCOPYvoid __fastcall MemCanvas::CanvasCopy(TCanvas * Canvas,TRect rc,int left,int top,int mode){   BitBlt(Canvas->Handle, rc.Left, rc.Top, rc.Width(), rc.Height(), m_hdcMemory, left, top, mode);}#endif

窗体的.h文件内容如下：

#ifndef Unit1H#define Unit1H//---------------------------------------------------------------------------#include <Classes.hpp>#include <Controls.hpp>#include <StdCtrls.hpp>#include <Forms.hpp>#include <ExtCtrls.hpp>#include "MemCanvas.h"//---------------------------------------------------------------------------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        MemCanvas * p1;        Gdiplus::Graphics *g;};//---------------------------------------------------------------------------extern PACKAGE TForm1 *Form1;//---------------------------------------------------------------------------#endif

在.cpp中调用如下：

//---------------------------------------------------------------------------#include <vcl.h>#pragma hdrstop#include "Unit1.h"//---------------------------------------------------------------------------#pragma package(smart_init)#pragma resource "*.dfm"TForm1 *Form1;//---------------------------------------------------------------------------__fastcall TForm1::TForm1(TComponent* Owner)        : TForm(Owner){        Image1->Parent->DoubleBuffered = true;        GdiplusStartup(&GdiplusToken,   &GdiplusStartupInput,   NULL);   //   初始化GDI+        //==============================        p1= new  MemCanvas; //创建内存位图对象        m_hdcMemory = p1->CreateMemCanvas(450,265);//创建内存位图句柄        g= new Gdiplus::Graphics(m_hdcMemory);//创建GDI+对象        //==================================}//---------------------------------------------------------------------------__fastcall  TForm1::~TForm1(void)   {        g->ReleaseHDC(m_hdcMemory);        GdiplusShutdown(GdiplusToken);   //   关闭GDI+        delete p1;}//---------------------------------------------------------------------------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];        g->Clear(13369376);        //==============================// 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;                //内存位图类方法        TRect rc(0,0,600,600);        //将内存中的位图复制到指定画布        p1->CanvasCopy(Image1->Canvas,rc,0,0,cmSrcCopy);        Image1->Repaint();//刷新画布}//---------------------------------------------------------------------------

上述代码参考过妖哥的一些代码。在C++builder6中编译通过。