使用 C/C++ 和 WinApi 精确绘制 1 像素宽度的线答案

【问题标题】：Draw exactly 1 pixel width line using C/C++ and WinApi使用 C/C++ 和 WinApi 精确绘制 1 像素宽度的线
【发布时间】：2016-06-17 13:58:36
【问题描述】：

我正在尝试使用 C/C++ 代码和 Win API 函数来画线。出于特定原因，我需要正好有 1 个像素的线宽，但我在屏幕上看到的完全不同。根据笔/画笔设置的方式，它可以是 2 或 3 像素宽的线条，而不是 1。只是为了测试，我尝试绘制 3 像素线，结果得到 5 像素。其他类型的绘图原语也是如此：圆角矩形、矩形、椭圆等。有什么方法可以禁用绘制线周围的这种阴影边界？绘图功能的代码示例如下。

void DisplayDrawings (HDC hDC, HWND hWnd)
{
 LOGBRUSH       stLogBrush; 
 RECT       rRect       = {0,0,0,0};
 HBITMAP        hBitmap     = NULL;
 HBRUSH     hBrush      = NULL;
 HGDIOBJ        hOldBrush       = NULL;  
 HGDIOBJ        hOldPen     = NULL;
 HPEN       hPen            = NULL;      
 BOOL       bB_Result       = FALSE;
 UINT       bBrushByBits [8];
 int            iRightPos       = 0;
 int            iLeftPos        = 30;
 int            iLineY      = 30;
 int            iDrawStep       = 10;   
 int            i           = 0;


#ifndef RGBA
    #define RGBA(r,g,b,a)        ((COLORREF)( (((DWORD)(BYTE)(a))<<24) |     RGB(r,g,b) ))
#endif
 SetBkMode (hDC, OPAQUE);
 bB_Result              = GetClientRect(hWnd, &rRect);
 if (bB_Result == FALSE)
    {
     return;
    }
 iRightPos              = rRect.right - 30 - 1;

 // Line 1. Draw 1 pixel Line using standard brush/pen. 

 hPen                   = CreatePen (PS_SOLID,1, RGB(255, 0,0));
 hOldPen                    = SelectObject (hDC, hPen);
 if (hOldPen == NULL)
    {
     return;
    }
 MoveToEx (hDC, iLeftPos,iLineY,NULL);
 LineTo (hDC,iRightPos,iLineY);
 SelectObject (hDC, hOldPen);
 DeleteObject (hPen);
 iLineY                 += iDrawStep;
 // Result - line with 2 pixels width   
 // Line 2. Draw 1 pixel Line using standard brush/pen, but setting pen width to "0".  CreatePen API says: "If nWidth is zero, the pen is a single pixel wide, regardless of the current transformation"
 hPen                   = CreatePen (PS_SOLID,0, RGB(255, 0,0));
 hOldPen                    = SelectObject (hDC, hPen);
 if (hOldPen == NULL)
    {
     return;
    }
 MoveToEx (hDC, iLeftPos,iLineY,NULL);
 LineTo (hDC,iRightPos,iLineY);
 SelectObject (hDC, hOldPen);
 DeleteObject (hPen);
 iLineY                 += iDrawStep;
 // Result - line with 3 pixels width
 // Line 3. Draw 1 pixel as above, but set current brush to NULL
 hOldBrush              = SelectObject (hDC, GetStockObject(NULL_BRUSH));
 if (hOldBrush == NULL)
    {
     return;
    }
 hPen                   = CreatePen (PS_SOLID,0, RGB(255, 0,0));
 hOldPen                    = SelectObject (hDC, hPen);
 if (hOldPen == NULL)
    {
     return;
    }
 MoveToEx (hDC, iLeftPos,iLineY,NULL);
 LineTo (hDC,iRightPos,iLineY);
 SelectObject (hDC, hOldPen);
 DeleteObject (hPen);
 SelectObject (hDC, hOldBrush);
 iLineY                 += iDrawStep;
 // Result - line with 2 pixels width
 // Line 4. Draw 3 pixel Line using standard brush/pen
 hPen                   = CreatePen (PS_SOLID,3, RGB(255, 0,0));
 hOldPen                    = SelectObject (hDC, hPen);
 if (hOldPen == NULL)
    {
     return;
    }
 MoveToEx (hDC, iLeftPos,iLineY,NULL);
 LineTo (hDC,iRightPos,iLineY);
 SelectObject (hDC, hOldPen);
 DeleteObject (hPen);
 iLineY                 += iDrawStep;
 // Result - line with 5 pixels width
  // Line 5. Draw 3 pixel as above, but set current brush to NULL
 hOldBrush              = SelectObject (hDC, GetStockObject(NULL_BRUSH));
 if (hOldBrush == NULL)
    {
     return;
    }
 hPen                   = CreatePen (PS_SOLID,3, RGB(255, 0,0));
 hOldPen                    = SelectObject (hDC, hPen);
 if (hOldPen == NULL)
    {
     return;
    }
 MoveToEx (hDC, iLeftPos,iLineY,NULL);
 LineTo (hDC,iRightPos,iLineY);
 SelectObject (hDC, hOldPen);
 DeleteObject (hPen);
 SelectObject (hDC, hOldBrush);
 iLineY                 += iDrawStep;
 // Result - line with 5 pixels width
 // Line 6. Draw 1 pixel line by creating own pen with monochrome 8x8 brush. Result is 3  
int k = 0;
 for(i = 0; i < 8; i++)
    {
     bBrushByBits [i]       = 0x00;
    }
 hBitmap                    = CreateBitmap(8, 8, 1, 1, (LPBYTE)bBrushByBits); 
 if (hBitmap == NULL)
    {
     return;
    }
 stLogBrush.lbColor         = RGBA(255,0,0,0);
 stLogBrush.lbHatch         = (ULONG_PTR) hBitmap; 
 stLogBrush.lbStyle         = BS_PATTERN;   

 hPen                   = ExtCreatePen (PS_GEOMETRIC, 3, &stLogBrush, 0, NULL); 
 hOldPen                    = SelectObject (hDC, hPen);
 if (hOldPen == NULL)
    {
     return;
    }
 MoveToEx (hDC, iLeftPos,iLineY,NULL);
 LineTo (hDC,iRightPos,iLineY);
 SelectObject (hDC, hOldPen);
 DeleteObject (hPen);
 DeleteObject (hBitmap);
 // Result - line with 2 pixels width

}

提前致谢

【问题讨论】：

CreatePen: "nWidth [in]: 笔的宽度，以逻辑单位为单位。如果 nWidth 为零，则无论当前的转变。”
在上面的代码中也是这样做的，但是宽度仍然是 3 或 2（如果画笔设置为 NULL_BRUSH）像素宽
如果一切都失败了，你可以把它弄成贫民窟，直接使用“SetPixel”。 msdn.microsoft.com/en-us/library/windows/desktop/…

标签： winapi draw gdi

【解决方案1】：

tl;dr：DPI 意识。

Windows 会为高 DPI 显示器放大图形，除非您明确告诉它您的程序了解如何使用实际 DPI。

您可以在应用程序的早期通过清单或系统调用来执行此操作。 API 的原始版本是 SetProcessDPIAware。较新的版本是 SetProcessDPIAwareness，即使在显示器具有不同 DPI 的多显示器系统上，它也可以让您告诉 Windows 您知道自己在做什么。

【讨论】：