Question

我使用GetDIBits()检索位图的位并将它们复制到缓冲区中。函数不会失败（结果与NULL不同），但是我得到错误的位图高度和错误的缓冲区。

这是我的代码的一部分：

HDC hdcMemDC = CreateCompatibleDC(hDC); // (hDC = hDC = BeginPaint(hwnd, &ps): i get it in WM_Paint)
int l_uiWidth = 400;
int l_uiHeight = 120;
HBITMAP hbmp = CreateCompatibleBitmap(hDC, l_uiWidth, l_uiHeight);
HGDIOBJ oldhbmp = SelectObject(hdcMemDC,hbmp);
BITMAPINFO   bi;
bi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
bi.bmiHeader.biWidth = l_uiWidth;
bi.bmiHeader.biHeight = l_uiHeight;
bi.bmiHeader.biPlanes = 1;
bi.bmiHeader.biBitCount = 8;
bi.bmiHeader.biCompression = BI_RGB;
bi.bmiHeader.biSizeImage = 0;
bi.bmiHeader.biXPelsPerMeter = 0;
bi.bmiHeader.biYPelsPerMeter = 0;
bi.bmiHeader.biClrUsed = 256;
bi.bmiHeader.biClrImportant = 0;
BYTE *l_ImagePDM = new BYTE[l_uiWidth * l_uiHeight];
GetDIBits(hdcMemDC,hbmp,0,l_uiHeight,l_Image,&bi,DIB_RGB_COLORS);

请帮帮我！我的代码出了什么问题？

Answer 1

您在查询位的位图上没有绘制任何内容。 CreateCompatibleBitmap()不会复制源HDC的像素。它仅分配与指定HBITMAP兼容的HDC，然后您可以选择HBITMAP到HDC。但是你仍然必须在位图上绘制一些内容，以使其内容有意义，然后再查询其位。

Answer 2

使用C ++ Builder时，可以使用Graphics单位处理图形。

从窗口复制内容的示例：

void __fastcall TForm1::Button1Click(TObject *Sender)
{
    // Create a bitmap
    Graphics::TBitmap* bit = new Graphics::TBitmap();
    bit->PixelFormat = pf24bit;
    bit->HandleType = bmDIB;
    bit->Width = 200;
    bit->Height = 200; // or bit->SetSize(200, 200) - newer versions C++ Builder

    // Copy something from this Form (from window)
    bit->Canvas->CopyRect(TRect(0, 0, 200, 200), this->Canvas, TRect(0, 0, 200, 200));

    // Do something with bitmap data
    RGBTRIPLE* line;
    for (int i = 0; i < bit->Height; i++)
    {
        // Get memory address from line i
        line = (RGBTRIPLE*) bit->ScanLine[i];

        // Change 5'th pixel
        line[5].rgbtRed = 255;
    }

    // Get whole bitmap memory. Bitmap data are stored upside down and size of each row is rounded
    // up to a multiple of 4 bytes.
    unsigned char* bitmem = (unsigned char*)(bit->ScanLine[ bit->Height-1 ]);
    //...

    // Draw bitmap on Form
    Canvas->Draw(0, 200, bit);

    delete bit;
}

当你有设备上下文时，你可以像这样使用TCanvas：

void __fastcall TForm1::Button2Click(TObject *Sender)
{
    // Create device context
    HDC hdc = GetDC(this->Handle); // or GetWindowDC - whole window with frame

    // Create canvas and associate device context
    TCanvas* canv = new TCanvas();
    canv->Handle = hdc;

    // Create a bitmap
    Graphics::TBitmap* bit = new Graphics::TBitmap();
    bit->PixelFormat = pf24bit;
    bit->HandleType = bmDIB;
    bit->Width = this->ClientWidth;
    bit->Height = this->ClientHeight; // or bit->SetSize(w, h) - newer versions C++ Builder

    // Copy window content
    TRect r(0, 0, this->ClientWidth, this->ClientHeight);
    bit->Canvas->CopyRect(r, canv, r);   //  USEING TCanvas

    // Release context and delete canvas
    ReleaseDC(this->Handle, hdc);
    delete canv;

    // Do something with the bitmap
    bit->SaveToFile("screenshot.bmp");
    delete bit;
}

您还可以将TCanvas用于BeginPaint的设备上下文：

canv->Handle = BeginPaint(hwnd, &ps);

GetDIBits（）构建器c ++的处理错误

2 个答案: