first pass at per window dpi, changes dynamically to dpi changes

SnapWindow.cpp

@@ -0,0 +1,104 @@
+#include "stdafx.h"
+#include "SnapWindow.h"
+
+
+SnapWindow::SnapWindow()
+{
+	snap_ModifierKey = VK_SHIFT;
+	NONCLIENTMETRICS ncm = { 0 };
+	ncm.cbSize = sizeof ncm;
+	SystemParametersInfo(SPI_GETNONCLIENTMETRICS, 0, &ncm, 0);
+	snap_Margin = ncm.iCaptionHeight;
+
+	snap_cur_pos.x = 0;
+	snap_cur_pos.y = 0;
+	snap_rcWindow.bottom = 0;
+	snap_rcWindow.left = 0;
+	snap_rcWindow.right = 0;
+	snap_rcWindow.top = 0;	
+	snap_x = 0;
+	snap_y = 0;
+}
+
+
+SnapWindow::~SnapWindow()
+{
+}
+
+BOOL SnapWindow::isSnapClose(int a, int b) 
+{
+	return (abs(a - b) < snap_Margin); 
+}
+
+LRESULT SnapWindow::OnSnapEnterSizeMove(HWND hWnd)
+{
+	snap_cur_pos.x = 0;
+	snap_cur_pos.y = 0;
+
+	snap_rcWindow.bottom = 0;
+	snap_rcWindow.left = 0;
+	snap_rcWindow.right = 0;
+	snap_rcWindow.top = 0;
+
+	GetWindowRect(hWnd, &snap_rcWindow);
+
+	GetCursorPos(&snap_cur_pos);
+
+	snap_x = snap_cur_pos.x - snap_rcWindow.left;
+	snap_y = snap_cur_pos.y - snap_rcWindow.top;
+
+	return 0;
+}
+
+LRESULT SnapWindow::OnSnapMoving(HWND hWnd, LPRECT snap_prc)
+{
+	//no snap if shift key pressed
+	if (GetAsyncKeyState(snap_ModifierKey) < 0) 
+		return FALSE;
+	
+	snap_cur_pos.x = 0;
+	snap_cur_pos.y = 0;
+	snap_rcWindow.bottom = 0;
+	snap_rcWindow.left = 0;
+	snap_rcWindow.right = 0;
+	snap_rcWindow.top = 0;
+
+	GetCursorPos(&snap_cur_pos);
+	OffsetRect(snap_prc,
+		snap_cur_pos.x - (snap_prc->left + snap_x),
+		snap_cur_pos.y - (snap_prc->top + snap_y));
+
+	//it may change during app lifetime
+	SystemParametersInfo(SPI_GETWORKAREA, 0, &snap_wa, 0);
+
+	MONITORINFO mi;
+	HMONITOR hMonitor = MonitorFromWindow(hWnd, MONITOR_DEFAULTTONEAREST);
+	mi.cbSize = sizeof(mi);
+	GetMonitorInfo(hMonitor, &mi);
+	snap_wa = mi.rcWork;
+
+	if (isSnapClose(snap_prc->left, snap_wa.left)) 
+	{ 
+		OffsetRect(snap_prc, snap_wa.left - snap_prc->left, 0); 
+	}
+	else
+	{
+		if (isSnapClose(snap_wa.right, snap_prc->right)) 
+		{ 
+			OffsetRect(snap_prc, snap_wa.right - snap_prc->right, 0); 
+		}
+	}
+
+	if (isSnapClose(snap_prc->top, snap_wa.top)) 
+	{ 
+		OffsetRect(snap_prc, 0, snap_wa.top - snap_prc->top); 
+	}
+	else
+	{
+		if (isSnapClose(snap_wa.bottom, snap_prc->bottom)) 
+		{ 
+			OffsetRect(snap_prc, 0, snap_wa.bottom - snap_prc->bottom); 
+		}
+	}
+	return TRUE;
+}

SnapWindow.h

@@ -0,0 +1,21 @@
+#pragma once
+class SnapWindow
+{
+public:
+	SnapWindow();
+	~SnapWindow();
+
+	int snap_Margin;
+	int snap_ModifierKey;
+	
+	LRESULT OnSnapMoving(HWND hWnd, LPRECT snap_prc);
+	LRESULT OnSnapEnterSizeMove(HWND hWnd);
+
+private:
+	POINT snap_cur_pos;
+	RECT snap_rcWindow, snap_wa, *snap_prc;
+	int snap_x, snap_y;
+
+	BOOL isSnapClose(int a, int b);
+};
+