用什么方法可以截取屏幕上指定区域的位图?

Question

用什么方法可以截取屏幕上指定区域的位图?

Answer 1

获得屏幕DC，然后BitBlt。仔细看BitBlt的参数就知道了。

Answer 2

HBITMAP CopyDCToBitmap(HDC hScrDC, LPRECT lpRect)
{
HDC        hMemDC; // 屏幕和内存设备描述表    
HBITMAP    hBitmap,hOldBitmap;  // 位图句柄
int       nX, nY, nX2, nY2;     // 选定区域坐标
int       nWidth, nHeight;      // 位图宽度和高度 if (IsRectEmpty(lpRect)) // 确保选定区域不为空矩形
return NULL;

// 获得选定区域坐标
nX = lpRect->left;
nY = lpRect->top;
nX2 = lpRect->right;
nY2 = lpRect->bottom;
nWidth = nX2 - nX;
nHeight = nY2 - nY;

hMemDC = CreateCompatibleDC(hScrDC);//为屏幕设备描述表创建兼容的内存设备描述表

// 创建一个与屏幕设备描述表兼容的位图
float factor = 1.0f;
hBitmap = CreateCompatibleBitmap(hScrDC, nWidth, nHeight);
while(!hBitmap)
{
factor -= 0.05f;
hBitmap = CreateCompatibleBitmap(hScrDC, (int)(nWidth*factor), (int)(nHeight*factor));
}
// 把新位图选到内存设备描述表中
hOldBitmap = (HBITMAP)SelectObject(hMemDC, hBitmap);
// 把屏幕设备描述表拷贝到内存设备描述表中
StretchBlt(hMemDC,0,0,nWidth,nHeight,hScrDC,nX,nY,nWidth,nHeight,SRCCOPY);
//BitBlt(hMemDC, 0, 0, nWidth, nHeight,hScrDC, nX, nY, SRCCOPY);
//得到屏幕位图的句柄  hBitmap = (HBITMAP)SelectObject(hMemDC, hOldBitmap);
//清除 

// DeleteDC(hScrDC);
DeleteDC(hMemDC);
DeleteObject(hOldBitmap);
// 返回位图句柄
return hBitmap;
}

Answer 3

这些方法都是copy特定窗口位图。我想要拷贝屏幕上任意指定区域的位图，其实就是屏幕抓图。

Answer 4

这是一个保存整个屏幕的,你可以改为保存一部分,代码是BCB下的:
Ddraw.cpp从SDK里找去
先要:    //初始化DirectDraw环境，并实现DirectDraw功能
    InitDDraw(lpDD,lpDDSPrimary)
最后要:
FreeDDraw(lpDD,lpDDSPrimary);保存的CPP
bool Is555=true;
inline unsigned char GetRed(WORD color)
{
if( Is555 )
return (color>>7) & 0xff;
else
return (color>>8) & 0xff;
}inline unsigned char GetGreen(WORD color)
{
if( Is555 )
return (color>>2) & 0xff;
else
return (color>>3) & 0xff;
}
inline unsigned char GetBlue(WORD color)
{
return (color & 0x1f) << 3;
}
bool SaveToBitmapFile(LPDIRECTDRAWSURFACE lpSurface, char* filename)
{
WORD* lpBuffer; // 表面指针
int nPitch;  // 表面跨距
int nWidth, nHeight; // 表面宽高///////////////
/////////////        HWND hwnd=GetActiveWindow();
// 打开文件s
FILE* fp;
if( (fp=fopen(filename, "wb")) != NULL )
{
// 锁定表面
DDSURFACEDESC ddsd;
ddsd.dwSize = sizeof(ddsd);
                ShowWindow(hwnd,SW_MINIMIZE);
HRESULT ddrval = lpSurface->Lock( NULL, &ddsd, DDLOCK_WAIT, NULL );
//                ddsd.lPitch//每行数据总字节数
//                ShowMessage("RM:"+AnsiString(ddsd.ddpfPixelFormat.dwRBitMask)+
//                        "GM:"+AnsiString(ddsd.ddpfPixelFormat.dwGBitMask)
//                        +"BM:"+AnsiString(ddsd.ddpfPixelFormat.dwBBitMask)
//                        +"lPitch:"+AnsiString(ddsd.lPitch));
if( ddrval == DD_OK )
{
   lpBuffer = (WORD *)ddsd.lpSurface;
nWidth = ddsd.dwWidth;
nHeight = ddsd.dwHeight;
nPitch  = ddsd.lPitch >> 1; //lPitch以Byte为单位，GraphPitch以WORD为单位。所以GraphPitch = lPitch / 2;
                        if(ddsd.ddpfPixelFormat.dwBBitMask==31)Is555=false;
} // 保存文件头
                fputc(0x42,fp);
                fputc(0x4d,fp);
                fputc( (nWidth * nHeight * 3 + 0x36)&0xff,fp);
                fputc(((nWidth * nHeight * 3 + 0x36)>>8)&0xff,fp);
                fputc(((nWidth * nHeight * 3 + 0x36)>>16)&0xff,fp);
                fputc(((nWidth * nHeight * 3 + 0x36)>>24)&0xff,fp);
                fputc(0,fp);fputc(0,fp);
                fputc(0,fp);fputc(0,fp);
                fputc(0x36,fp);
                fputc(0,fp);fputc(0,fp);fputc(0,fp); // 保存文件信息
BITMAPINFOHEADER Header;
Header.biSize = sizeof(BITMAPINFOHEADER);// 结构的大小
Header.biWidth = nWidth;  // 宽
Header.biHeight = nHeight;// 高
Header.biPlanes = 1;   // 固定
Header.biBitCount = 24;   // 颜色数
Header.biCompression = BI_RGB; // 是否压缩
Header.biSizeImage = nWidth * nHeight * 3;// 图片的大小
Header.biXPelsPerMeter = 0;
Header.biYPelsPerMeter = 0;
Header.biClrUsed = 0;
Header.biClrImportant = 0;
fwrite(&Header, Header.biSize, 1, fp);
// 写入具体内容(从下向上存放)
fseek(fp, 0x36, SEEK_SET);
            switch(ddsd.ddpfPixelFormat.dwRGBBitCount)
            {
               case 8:
                 {
                      BYTE *tem=(BYTE *)ddsd.lpSurface;
                      PALETTEENTRY entry[256];
                      HDC hScrDC=CreateDC("DISPLAY",NULL,NULL,NULL);
                      ::GetSystemPaletteEntries(hScrDC,0,256,entry);
                          for(int y=(int)nHeight-1;y>=0;y--)
                          {
                             for(int x=0;x<(int)nWidth;x++)
                             {
                                 fputc(entry[tem[x+ddsd.lPitch*y]].peBlue,fp);
                                 fputc(entry[tem[x+ddsd.lPitch*y]].peGreen,fp);
                                 fputc(entry[tem[x+ddsd.lPitch*y]].peRed,fp);
                             }
                          }
                      DeleteDC(hScrDC);
                          break;
                 }
               case 16:
         { WORD word;
         lpBuffer += nWidth * (nHeight - 1);
         for(int i=0; i<nHeight; i++)
        {
         for(int j=0; j<nWidth; j++)
         {
         word = *lpBuffer;
         fputc( GetBlue( word ), fp); // 蓝
        fputc( GetGreen( word ), fp); // 绿
         fputc( GetRed( word ), fp);     // 红         lpBuffer++;
         }
         lpBuffer -= nPitch*2; // 指针转到上一行的开始
         }
                        break;
                  }
               case 24:
//               case 32:
                  {
                      BYTE *tem=(BYTE *)ddsd.lpSurface;
                      tem+=nWidth * (nHeight - 1)*3;
//                      ShowMessage(AnsiString(ddsd.lPitch));
                      for(int y=(int)nHeight-1;y>=0;y--)
                          {
                             for(int x=0;x<(int)nWidth;x++)
                             {
                                 fputc(*tem++,fp);
                                 fputc(*tem++,fp);
                                 fputc(*tem++,fp);
                             }
                             tem-=ddsd.lPitch*2;
                          }
                          break;
                  }
                case 32:
                  {
                      BYTE *tem=(BYTE *)ddsd.lpSurface;
                      tem+=nWidth * (nHeight - 1)*4;
//                      ShowMessage(AnsiString(ddsd.lPitch));
                      for(int y=(int)nHeight-1;y>=0;y--)
                          {
                             for(int x=0;x<(int)nWidth;x++)
                             {                                 fputc(*tem++,fp);
                                 fputc(*tem++,fp);
                                 fputc(*tem++,fp);
                                 tem++;
                              }
                             tem-=ddsd.lPitch*2;
                          }
                          break;
                  }
             }//end switch fclose(fp); // 解锁表面
ddrval = lpSurface->Unlock( NULL );
                PostMessage(hwnd,WM_QUIT,0,0);
return true;
} return false;
}