Draw exactly 1 pixel width line using C/C++ and WinApi - winapi

Question

I am trying to draw the line using C/C++ code and Win API functions. For the specific reason I need to have exactly 1 pixel line width, but what I am getting on the screen is completely different. Depending on the ways of Pen/Brush settings it could be either 2 or 3 pixels wide line and never 1.
Just for the test I’ve tried to draw 3 pixels line and as a result getting 5 pixels.
The same story with other kind of drawing primitives: rounded rectangles, rectangles, ellipses etc.
Is there any way to disable such shadow bounding around drawn lines?
Code sample of drawing function is below.
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
}
Thanks in advance

Answer 1

tl;dr: DPI Awareness.
Windows scales graphics up for high-DPI monitors unless you explicitly tell it that your program understands how to work with the actual DPI.
You can do this with a manifest or a system call very early in your application. The original version of the API was SetProcessDPIAware. The newer version is SetProcessDPIAwareness, which lets you tell Windows you know what your doing even on a multi-monitor system where the monitors have different DPIs.