GDI+字体渲染，尤其是在分层窗口中

Question

我的朋友们，这将会很长......

当我尝试在分层窗口中渲染文本时，我遇到了一些非常奇怪的行为。

奇怪的是，对于一些font/font-style/font-size的组合，GDI+改变了渲染方式。对于 Tahoma-Bold 字体大小在 8.49 和 16.49（像素单位）之间（包括“失败”）。对于其他字体和样式，我在不同尺寸下都会“失败”。

为了清楚起见，我在下面提供了一个完整的可执行示例。 这两个关键要使用的参数位于第 23 行：

Color g_oTextColor( 255, 240, 0, 0 ); // Simply change Color to ( 254, 240, 0, 0 ) [to add slight transparency] and everything will work!
#define USE_LAYERED_WINDOW // or just comment this line out [to use a regular window], and everything will work!

---

当使用分层窗口和完全不透明时，字体会在背景中绘制一个透明的“洞”。但是，如果我为文本颜色添加轻微的透明度（alpha 通道 = 254），字体就会变得不透明。或者，如果我使用常规（非分层）窗口，字体会呈现不透明。 这里发生了什么？

但即使没有分层/透明度问题，很明显这里正在发生一些奇怪的事情。字体大小 8.49 - 16.48 的渲染像素完美，其他字体有轻微的模糊质量，尤其是小字体。因此，系统似乎采用了不同的方法来渲染这些中等尺寸。 有人能解释一下吗，我怎样才能渲染例如 8.0 像素大小的字体而不出现上面的模糊？我已经尝试了 SetTextRenderingHint() 的各种设置，并且SetTextContrast() 但对于 8 号字体来说，没有一个看起来很清晰。我尝试过 Tahoma &仅 Arial...

---

附带问题 1： 我想使用纯 GDI+ 进行离屏绘图，但我无法通过简单地创建位图和位图来使其工作。 图形对象。我仍然必须使用旧的 GDI 东西来创建 DC 并在其中选择 HBitmap。我怎样才能在 GDI+ 中完成这一切？

附带问题 2（仅限极客）： 我还尝试在老式 GDI 中绘制字体，但在那里我得到了一些更奇怪的效果：(1) 在分层窗口中，文本变得透明，但在添加剂中 方式。 （因此，如果后面的窗口是黑色的，那么红色文本看起来不错，但如果后面的窗口是白色的，则文本完全消失！）此外，如果我用半透明的正方形填充自己的窗口，那么它的行为就会如预期。 （如果红色方块后面的窗户是黑色的，那么它会变成深红色，而在白色窗户上的方块会变成浅红色）。我可以在一个分层窗口中同时观察这两种行为。 (2) 作为一个非常不受欢迎的奖励，绘制的文本失去了命中测试并且变得不可点击？ 有什么解释吗？

如果您已经读到这里，感谢您的耐心等待，并感谢您的回答！

// Create as a console application project
// + Unicode charset
// + Precompiled headers off
// + make sure to add linker input: gdiplus.lib

#ifndef _WIN32_WINNT        // Allow use of features specific to Windows XP or later.                   
#define _WIN32_WINNT 0x0501 // Change this to the appropriate value to target other versions of Windows.
#endif                      

// Standard and GDI+ stuffstuff 
#include <stdio.h>
#include <tchar.h>
#include <windows.h>
#include <iostream>
#include <cassert>
#include <Gdiplus.h>
using namespace Gdiplus;
GdiplusStartupInput g_oGdiPlusStartupInput;
ULONG_PTR g_pGdiPlusToken = NULL;


// #*#*#*#*#*#*#*#*# LINES TO CHANGE ---------->---------->---------->
Color g_oTextColor( 255, 240, 0, 0 ); // Simply change Color to ( 254, 240, 0, 0 ) [to add slight transparency] and everything will work!
#define USE_LAYERED_WINDOW // or just comment this line out [to use a regular window], and everything will work!


// Forward declarations
void RegWndClass();
LRESULT CALLBACK WndProc( HWND hWnd, UINT uiMsg, WPARAM wParam, LPARAM lParam );
void CreateWindows();
void Draw();
void MsgLoop();

// Other Globals
ATOM g_iWndClass = 0;
HWND g_hWndGdiPlus = NULL;
HWND g_hWndGdi = NULL;
const wchar_t* g_pWndClass = L"TST";
int g_iWidth = 200;
int g_iHeight = 200;

// Main entry-point
int _tmain( int argc, _TCHAR* argv[] )
{
    GdiplusStartup( &g_pGdiPlusToken, &g_oGdiPlusStartupInput, NULL );

    RegWndClass();
    CreateWindows();
    Draw();

    MsgLoop();

    ::UnregisterClass( g_pWndClass, NULL );
    ::Sleep( 500 );


    GdiplusShutdown( g_pGdiPlusToken );

    return 0;
} // _tmain

void CreateWindows()
{
#ifdef USE_LAYERED_WINDOW
        // The key trick is to create a window with style WS_EX_LAYERED, but WITHOUT any subsequent calls to SetLayeredWindowAttributes()
        // This gives us a magic window that must be updated with UpdateLayeredWindow() ( and it does NOT recieve any WM_PAINT messages )
        // as brilliantly described in: http://alexkr.com/source-code/50/layered-windows-and-updatelayeredwindow/
        g_hWndGdiPlus = ::CreateWindowEx( WS_EX_LAYERED, g_pWndClass, L"", WS_POPUP | WS_VISIBLE, 1000, 200, g_iWidth, g_iHeight, NULL, NULL, NULL, NULL ); 
#else
        g_hWndGdiPlus = ::CreateWindowEx( 0, g_pWndClass, L"", WS_OVERLAPPEDWINDOW | WS_POPUP | WS_VISIBLE, 1000, 200, g_iWidth, g_iHeight, NULL, NULL, NULL, NULL ); 
#endif

    //g_hWndGdi = ::CreateWindowEx( WS_EX_LAYERED, g_pWndClass, L"", WS_POPUP | WS_VISIBLE, 720, 500, 200, 200, NULL, NULL, NULL, NULL ); 

} // CreateWindows

void Draw()
{
    // Init GDI+ surface
    HDC hOff = ::CreateCompatibleDC( NULL );
    Bitmap oDaBigOne( g_iWidth, g_iHeight, PixelFormat32bppARGB );
    HBITMAP hBMit =  NULL;
    Color oCol( 0, 0, 0, 0 );
    oDaBigOne.GetHBITMAP( oCol, &hBMit );
    HGDIOBJ hSave = ::SelectObject( hOff, hBMit );

#ifdef USE_LAYERED_WINDOW
        Graphics oGraph( hOff );
#else
        Graphics oGraph( g_hWndGdiPlus );
#endif

    oGraph.Clear( Color( 255, 55, 155, 255 ) );

    // Draw text
    oGraph.SetTextRenderingHint( TextRenderingHintAntiAliasGridFit );
    oGraph.SetTextContrast( 0xffffffff );
    oGraph.SetCompositingMode( CompositingModeSourceOver );
    oGraph.SetCompositingQuality( CompositingQualityHighQuality );
    oGraph.SetPixelOffsetMode( PixelOffsetModeHighQuality );

    const FontFamily oFamily( L"Tahoma", NULL );

#if 1 // Use bold
    Font oF600( &oFamily, 6.00, FontStyle::FontStyleBold, Unit::UnitPixel );
    Font oF800( &oFamily, 8.00, FontStyle::FontStyleBold, Unit::UnitPixel );
    Font oF848( &oFamily, 8.48, FontStyle::FontStyleBold, Unit::UnitPixel );
    Font oF849( &oFamily, 8.49, FontStyle::FontStyleBold, Unit::UnitPixel );
    Font oF1200( &oFamily, 12.00, FontStyle::FontStyleBold, Unit::UnitPixel );
    Font oF1500( &oFamily, 15.00, FontStyle::FontStyleBold, Unit::UnitPixel );
    Font oF1648( &oFamily, 16.48, FontStyle::FontStyleBold, Unit::UnitPixel );
    Font oF1649( &oFamily, 16.49, FontStyle::FontStyleBold, Unit::UnitPixel );
#else // Use regular
    Font oF600( &oFamily, 6.00, FontStyle::FontStyleRegular, Unit::UnitPixel );
    Font oF800( &oFamily, 8.00, FontStyle::FontStyleRegular, Unit::UnitPixel );
    Font oF848( &oFamily, 8.48, FontStyle::FontStyleRegular, Unit::UnitPixel );
    Font oF849( &oFamily, 8.49, FontStyle::FontStyleRegular, Unit::UnitPixel );
    Font oF1200( &oFamily, 12.00, FontStyle::FontStyleRegular, Unit::UnitPixel );
    Font oF1500( &oFamily, 15.00, FontStyle::FontStyleRegular, Unit::UnitPixel );
    Font oF1648( &oFamily, 16.48, FontStyle::FontStyleRegular, Unit::UnitPixel );
    Font oF1649( &oFamily, 16.49, FontStyle::FontStyleRegular, Unit::UnitPixel );
#endif

    assert( oF600.GetLastStatus() == Ok ); // Make sure font is OK

    SolidBrush oBrush( g_oTextColor ); 

    double dy = 1.0;
    oGraph.DrawString( L"Size 6.00", -1, &oF600, PointF( 30.0, dy += 18.0 ), &oBrush );
    oGraph.DrawString( L"Size 8.00", -1, &oF800, PointF( 30.0, dy += 18.0 ), &oBrush );
    oGraph.DrawString( L"Size 8.48", -1, &oF848, PointF( 30.0, dy += 18.0 ), &oBrush );
    oGraph.DrawString( L"Size 8.49", -1, &oF849, PointF( 30.0, dy += 18.0 ), &oBrush );
    oGraph.DrawString( L"Size 12.00", -1, &oF1200, PointF( 30.0, dy += 18.0 ), &oBrush );
    oGraph.DrawString( L"Size 15.00", -1, &oF1500, PointF( 30.0, dy += 18.0 ), &oBrush );
    oGraph.DrawString( L"Size 16.48", -1, &oF1648, PointF( 30.0, dy += 18.0 ), &oBrush );
    oGraph.DrawString( L"Size 16.49", -1, &oF1649, PointF( 30.0, dy += 18.0 ), &oBrush );

#ifndef USE_LAYERED_WINDOW
    return;
#endif

    // Do da layered window magic stuff
    BLENDFUNCTION oBF = { 0 };
    oBF.BlendOp = AC_SRC_OVER;
    oBF.BlendFlags = 0;
    oBF.SourceConstantAlpha = 255;
    oBF.AlphaFormat = AC_SRC_ALPHA;

    SIZE oSize = { 0 };
    oSize.cx = g_iWidth;
    oSize.cy = g_iHeight;

    POINT oPTZero = { 0 };

    RECT oRect = { 0 };
    ::GetWindowRect( g_hWndGdiPlus, &oRect );

    POINT oPTWnd = { 0 };

    oPTWnd.x = oRect.left;
    oPTWnd.y = oRect.top;

    //HDC hDC = oGraph.GetHDC();
    BOOL bOK = ::UpdateLayeredWindow( g_hWndGdiPlus,
        NULL, //HDC hdcDst,
        &oPTWnd, // POINT &oPtNull,
        &oSize, // SIZE *psize,
        hOff, // HDC hdcSrc,
        &oPTZero, // POINT *pptSrc,
        RGB(255,255,255), // COLORREF crKey,
        &oBF, // BLENDFUNCTION *pblend,
        ULW_ALPHA // DWORD dwFlags
    );
} // Draw

void MsgLoop()
{
    ::SetTimer( g_hWndGdiPlus, 0, 19999, NULL ); // Self-destruct timer

    MSG msg = { 0 };
    while ( ::GetMessage( &msg, NULL, 0, 0 ) )
    {
            ::TranslateMessage(&msg);
            ::DispatchMessage(&msg);
    }
} // MsgLoop

void RegWndClass()
{

        WNDCLASSEX wcex = { 0 };

        wcex.cbSize          = sizeof(WNDCLASSEX);
        wcex.style           = CS_HREDRAW | CS_VREDRAW | CS_OWNDC;
        wcex.lpfnWndProc     = WndProc;
        wcex.cbClsExtra      = 0;
        wcex.cbWndExtra      = 8; // 8 bytes, to allow for 64-bit architecture
        wcex.hInstance       = NULL; // CHECK
        wcex.hIcon           = NULL;
        wcex.hCursor         = ::LoadCursor(NULL, IDC_ARROW);
        wcex.hbrBackground   = (HBRUSH)NULL_BRUSH; // CHECK
        wcex.lpszMenuName    = NULL;
        wcex.lpszClassName   = g_pWndClass;
        wcex.hIconSm         = NULL;

        g_iWndClass = ::RegisterClassEx(&wcex);
} // RegWndClass

LRESULT CALLBACK WndProc( HWND hWnd, UINT uiMsg, WPARAM wParam, LPARAM lParam )
{
    switch( uiMsg )
    {
        case WM_TIMER:
        {
            std::wstring s;
            std::wcout <<  L"Let´s quit" ;
            ::PostQuitMessage( 0 );
            return 0;
        }
        case WM_PAINT:
            Draw();
            break;

        default:
        {
            return DefWindowProc( hWnd, uiMsg, wParam, lParam );
        }
    }
    return DefWindowProc( hWnd, uiMsg, wParam, lParam );
} // WndProc

[编辑]问题解决了！ 以下代码根据 Rodrogo 的出色建议编写。 向他致以崇高的敬意和衷心的感谢。我真的很感激。

所有编辑都标有//#MOD

// Create as a console application project
// + Unicode charset
// + Precompiled headers off
// + make sure to add linker input: gdiplus.lib

#ifndef _WIN32_WINNT        // Allow use of features specific to Windows XP or later.                   
#define _WIN32_WINNT 0x0501 // Change this to the appropriate value to target other versions of Windows.
#endif                      

// Standard stuff
#include <stdio.h>
#include <tchar.h>
#include <windows.h>
#include <iostream>
#include <cassert>

// GDI+ stuff
#include <Gdiplus.h>
using namespace Gdiplus;
GdiplusStartupInput g_oGdiPlusStartupInput;
ULONG_PTR g_pGdiPlusToken = NULL;




// #*#*#*#*#*#*#*#*# LINES TO CHANGE ---------->---------->---------->
Color g_oTextColor( 255, 240, 0, 0 ); // Simply change Color to ( 254, 240, 0, 0 ) [to add slight transparency] and everything will work!
#define USE_LAYERED_WINDOW // or just omment this line [to use a regular window], and everything will work!






// Forward declarations
void RegWndClass();
LRESULT CALLBACK WndProc( HWND hWnd, UINT uiMsg, WPARAM wParam, LPARAM lParam );
void CreateWindows();
void Draw();
void MsgLoop();

// Other Globals
ATOM g_iWndClass = 0;
HWND g_hWndGdiPlus = NULL;
HWND g_hWndGdi = NULL;
const wchar_t* g_pWndClass = L"TST";
int g_iWidth = 200;
int g_iHeight = 200;

// Main entry-point
int _tmain( int argc, _TCHAR* argv[] )
{
    GdiplusStartup( &g_pGdiPlusToken, &g_oGdiPlusStartupInput, NULL );

    RegWndClass();
    CreateWindows();
    Draw();

    MsgLoop();

    ::UnregisterClass( g_pWndClass, NULL );
    ::Sleep( 500 );


    GdiplusShutdown( g_pGdiPlusToken );

    return 0;
} // _tmain

void CreateWindows()
{
#ifdef USE_LAYERED_WINDOW
        // The key trick is to create a window with style WS_EX_LAYERED, but WITHOUT any subsequent calls to SetLayeredWindowAttributes()
        // This gives us a magic window that must be updated with UpdateLayeredWindow() ( and it does NOT recieve any WM_PAINT messages )
        // as brilliantly described in: http://alexkr.com/source-code/50/layered-windows-and-updatelayeredwindow/
        g_hWndGdiPlus = ::CreateWindowEx( WS_EX_LAYERED, g_pWndClass, L"", WS_POPUP | WS_VISIBLE, 1000, 200, g_iWidth, g_iHeight, NULL, NULL, NULL, NULL ); 
#else
        g_hWndGdiPlus = ::CreateWindowEx( 0, g_pWndClass, L"", WS_OVERLAPPEDWINDOW | WS_POPUP | WS_VISIBLE, 1000, 200, g_iWidth, g_iHeight, NULL, NULL, NULL, NULL ); 
#endif

    //g_hWndGdi = ::CreateWindowEx( WS_EX_LAYERED, g_pWndClass, L"", WS_POPUP | WS_VISIBLE, 720, 500, 200, 200, NULL, NULL, NULL, NULL ); 

} // CreateWindows

void Draw()
{
    // Init GDI+ surface
    HDC hOff = ::CreateCompatibleDC( NULL );
    Bitmap oDaBigOne( g_iWidth, g_iHeight, PixelFormat32bppARGB );
    HBITMAP hBMit =  NULL;
    Color oCol( 0, 0, 0, 0 );
    // oDaBigOne.GetHBITMAP( oCol, &hBMit ); //#MOD
    // HGDIOBJ hSave = ::SelectObject( hOff, hBMit ); //#MOD


    { // Limit oGraph scope //#MOD
#ifdef USE_LAYERED_WINDOW
        //Graphics oGraph( hOff ); //#MOD
        Graphics oGraph( &oDaBigOne ); //#MOD
#else
        Graphics oGraph( g_hWndGdiPlus );
#endif

    oGraph.Clear( Color( 255, 55, 155, 255 ) );

    // Draw text
    oGraph.SetTextRenderingHint( TextRenderingHintAntiAliasGridFit );
    oGraph.SetCompositingMode( CompositingModeSourceOver );
    oGraph.SetCompositingQuality( CompositingQualityHighQuality );
    oGraph.SetPixelOffsetMode( PixelOffsetModeHighQuality );

    const FontFamily oFamily( L"Tahoma", NULL );

#if 1 // Use bold
    Font oF600( &oFamily, 6.00, FontStyle::FontStyleBold, Unit::UnitPixel );
    Font oF848( &oFamily, 8.48, FontStyle::FontStyleBold, Unit::UnitPixel );
    Font oF849( &oFamily, 8.49, FontStyle::FontStyleBold, Unit::UnitPixel );
    Font oF1200( &oFamily, 12.00, FontStyle::FontStyleBold, Unit::UnitPixel );
    Font oF1500( &oFamily, 15.00, FontStyle::FontStyleBold, Unit::UnitPixel );
    Font oF1648( &oFamily, 16.48, FontStyle::FontStyleBold, Unit::UnitPixel );
    Font oF1649( &oFamily, 16.49, FontStyle::FontStyleBold, Unit::UnitPixel );
#else // Use regular
    Font oF600( &oFamily, 6.00, FontStyle::FontStyleRegular, Unit::UnitPixel );
    Font oF848( &oFamily, 8.48, FontStyle::FontStyleRegular, Unit::UnitPixel );
    Font oF849( &oFamily, 8.49, FontStyle::FontStyleRegular, Unit::UnitPixel );
    Font oF1200( &oFamily, 12.00, FontStyle::FontStyleRegular, Unit::UnitPixel );
    Font oF1500( &oFamily, 15.00, FontStyle::FontStyleRegular, Unit::UnitPixel );
    Font oF1648( &oFamily, 16.48, FontStyle::FontStyleRegular, Unit::UnitPixel );
    Font oF1649( &oFamily, 16.49, FontStyle::FontStyleRegular, Unit::UnitPixel );
#endif

    assert( oF600.GetLastStatus() == Ok ); // Make sure font is OK

    SolidBrush oBrush( g_oTextColor ); 

    double dy = 10.0;
    oGraph.DrawString( L"Size 6.00", -1, &oF600, PointF( 30.0, dy += 18.0 ), &oBrush );
    oGraph.DrawString( L"Size 8.48", -1, &oF848, PointF( 30.0, dy += 18.0 ), &oBrush );
    oGraph.DrawString( L"Size 8.49", -1, &oF849, PointF( 30.0, dy += 18.0 ), &oBrush );
    oGraph.DrawString( L"Size 12.00", -1, &oF1200, PointF( 30.0, dy += 18.0 ), &oBrush );
    oGraph.DrawString( L"Size 15.00", -1, &oF1500, PointF( 30.0, dy += 18.0 ), &oBrush );
    oGraph.DrawString( L"Size 16.48", -1, &oF1648, PointF( 30.0, dy += 18.0 ), &oBrush );
    oGraph.DrawString( L"Size 16.49", -1, &oF1649, PointF( 30.0, dy += 18.0 ), &oBrush );

#ifndef USE_LAYERED_WINDOW
    return;
#endif
    } // Limit oGraph scope //#MOD

    // Do da layered window magic stuff
    BLENDFUNCTION oBF = { 0 };
    oBF.BlendOp = AC_SRC_OVER;
    oBF.BlendFlags = 0;
    oBF.SourceConstantAlpha = 255;
    oBF.AlphaFormat = AC_SRC_ALPHA;

    SIZE oSize = { 0 };
    oSize.cx = g_iWidth;
    oSize.cy = g_iHeight;

    POINT oPTZero = { 0 };

    RECT oRect = { 0 };
    ::GetWindowRect( g_hWndGdiPlus, &oRect );

    POINT oPTWnd = { 0 };

    oPTWnd.x = oRect.left;
    oPTWnd.y = oRect.top;

    oDaBigOne.GetHBITMAP( oCol, &hBMit ); //#MOD
    HGDIOBJ hSave = ::SelectObject( hOff, hBMit ); //#MOD

    //HDC hDC = oGraph.GetHDC();
    BOOL bOK = ::UpdateLayeredWindow( g_hWndGdiPlus,
        NULL, //HDC hdcDst,
        &oPTWnd, // POINT &oPtNull,
        &oSize, // SIZE *psize,
        hOff, // HDC hdcSrc,
        &oPTZero, // POINT *pptSrc,
        RGB(255,255,255), // COLORREF crKey,
        &oBF, // BLENDFUNCTION *pblend,
        ULW_ALPHA // DWORD dwFlags
    );
} // Draw

void MsgLoop()
{
    ::SetTimer( g_hWndGdiPlus, 0, 19999, NULL ); // Self-destruct timer

    MSG msg = { 0 };
    while ( ::GetMessage( &msg, NULL, 0, 0 ) )
    {
            ::TranslateMessage(&msg);
            ::DispatchMessage(&msg);
    }
} // MsgLoop

void RegWndClass()
{

        WNDCLASSEX wcex = { 0 };

        wcex.cbSize          = sizeof(WNDCLASSEX);
        wcex.style           = CS_HREDRAW | CS_VREDRAW | CS_OWNDC;
        wcex.lpfnWndProc     = WndProc;
        wcex.cbClsExtra      = 0;
        wcex.cbWndExtra      = 8; // 8 bytes, to allow for 64-bit architecture
        wcex.hInstance       = NULL; // CHECK
        wcex.hIcon           = NULL;
        wcex.hCursor         = ::LoadCursor(NULL, IDC_ARROW);
        wcex.hbrBackground   = (HBRUSH)NULL_BRUSH; // CHECK
        wcex.lpszMenuName    = NULL;
        wcex.lpszClassName   = g_pWndClass;
        wcex.hIconSm         = NULL;

        g_iWndClass = ::RegisterClassEx(&wcex);
} // RegWndClass

LRESULT CALLBACK WndProc( HWND hWnd, UINT uiMsg, WPARAM wParam, LPARAM lParam )
{
    switch( uiMsg )
    {
        case WM_TIMER:
        {
            std::wstring s;
            std::wcout <<  L"Let´s quit" ;
            ::PostQuitMessage( 0 );
            return 0;
        }
        case WM_PAINT:
            Draw();
            break;

        default:
        {
            return DefWindowProc( hWnd, uiMsg, wParam, lParam );
        }
    }
    return DefWindowProc( hWnd, uiMsg, wParam, lParam );
} // WndProc

Answer 1

我认为问题在于 GDI（没有 +）不能很好地支持 alpha 透明度。最好的情况是，它保持 Alpha 通道不受影响。

当您使用具有 Alpha 通道的所选位图的 HDC 构建 Graphics 对象时……事情会变得很糟糕。我的猜测是GDI+字体光栅化根据很多参数决定使用哪种方法来渲染；然后，如果 GDI 恰好支持该方法，则会使用该方法（并且忽略 alpha 通道）；如果 GDI 不支持渲染方法，它将回退到逐像素渲染或类似方法，并且将正确使用 alpha 通道。

因此，要获得正确的结果，您不应使用 HDC 修改 Alpha 通道。尝试以下更改：

• 使用位图创建 Graphics 对象，而不是 HDC：

  图形 oGraph( &oDaBigOne );
  

• 仅在渲染完成后才将位图选择到 HDC hOff 中。为了确保最好销毁 Graphics 对象，使用 { ... } 限制其范围。

[编辑]

在新代码之后，解决方案很简单：不仅应该在绘制之后将调用移至 SelectObject()，还应将调用移至 GetBitmap()。也就是说，这两个函数应该位于调用 :UpdateLayeredWindow() 之前：

oDaBigOne.GetHBITMAP( oCol, &hBMit );
HGDIOBJ hSave = ::SelectObject( hOff, hBMit );

Answer 2

我想，我昨天找到了一个（部分）解决方案，它可能比 rodrigo 建议的更容易实现：您可以简单地将 StringFormatFlags::StringFormatFlagsBypassGDI 指定为格式标志您传递给 DrawString 的 StringFormat 实例，瞧：所有内容都使用支持 alpha 的字体渲染器进行绘制。这解决了 alpha 通道问题，至少......

Answer 3

我有一段时间无法找到这种奇怪行为的解释。但是，我确实发现使用默认渲染值可以为某些字体提供更好的结果，请尝试使用以下设置的 Arial：

oGraph.SetTextRenderingHint( TextRenderingHintAntiAliasGridFit );
oGraph.SetPixelOffsetMode( PixelOffsetModeDefault );
oGraph.SetCompositingMode( CompositingModeSourceOver );
oGraph.SetCompositingQuality( CompositingQualityDefault );

Answer 4

尝试将 PixelFormat32bppARGB 替换为 PixelFormat32bppPARGB。 BLENDFUNCTION 结构的文档指出它需要在源代码中预乘 alpha。