Fix file viewer layout

If scaling > 100% is enabled on the primary display, the controls in
the dialog window get bigger.  The file viewer uses hard-coded values
for the initial and minimum window size, which causes the expanded
controls to draw on top of each other.  (Issue #53.)

We now query the system for the scale factor, and adjust the window
size accordingly.

app/Preferences.cpp

@@ -247,16 +247,20 @@ Preferences::Preferences(void)
 
     SetPrefString(kPrViewTextTypeFace, L"Courier New");
     SetPrefLong(kPrViewTextPointSize, 10);
-    long width = 680 +  /* exact width for 80-column text */
-            ::GetSystemMetrics(SM_CXVSCROLL);
-    long height = 516;  /* exact height for file viewer to show IIgs graphic */
+
+    float scaleFactor = GetDesktopScaleFactor();
+    /* exact width for 80-column text; note text is scaled up */
+    long width = (int)(680 * scaleFactor) + ::GetSystemMetrics(SM_CXVSCROLL);
+    /* exact height for file viewer to show IIgs graphic at 1.0x */
+    long height = (int)(516 * scaleFactor);
+
     if (GetSystemMetrics(SM_CXSCREEN) < width)
         width = GetSystemMetrics(SM_CXSCREEN);
     if (GetSystemMetrics(SM_CYSCREEN) < height)
         height = GetSystemMetrics(SM_CYSCREEN); // may overlap system bar
-    //width = 640; height = 480;
     SetPrefLong(kPrFileViewerWidth, width);
     SetPrefLong(kPrFileViewerHeight, height);
+
     SetPrefLong(kPrDiskImageCreateFormat, -1);
 }
 

app/ViewFilesDialog.cpp

@@ -154,8 +154,12 @@ void ViewFilesDialog::OnCancel(void)
 
 void ViewFilesDialog::OnGetMinMaxInfo(MINMAXINFO* pMMI)
 {
-    pMMI->ptMinTrackSize.x = 664;
-    pMMI->ptMinTrackSize.y = 200;
+    float scaleFactor = GetDesktopScaleFactor();
+
+    // 664x200 was determined empirically to fit all controls.  The initial
+    // window size is set over in the Preferences constructor.
+    pMMI->ptMinTrackSize.x = (int)(664 * scaleFactor);
+    pMMI->ptMinTrackSize.y = (int)(200 * scaleFactor);
 }
 
 void ViewFilesDialog::OnSize(UINT nType, int cx, int cy)

util/Util.cpp

@@ -417,6 +417,27 @@ void CheckedLoadString(CString* pString, UINT nID)
     }
 }
 
+float GetDesktopScaleFactor()
+{
+    // The current scale factor for controls is determined by the settings
+    // for the main display at the time the application was launched.  If we
+    // don't do this, the controls will get all scrunched together if the
+    // scale is over 100% (issue #53).  The settings API doesn't seem to
+    // allow scaling things down, so we're only worried about expansion here.
+    //
+    // https://docs.microsoft.com/en-us/windows-hardware/manufacture/desktop/dpi-related-apis-and-registry-settings?view=windows-11#primary-display-dpi-scale-factor
+    // Get desktop dc
+    HDC desktopDc = ::GetDC(NULL);
+    // Get native resolution
+    int horizontalDPI = GetDeviceCaps(desktopDc, LOGPIXELSX);
+    int verticalDPI = GetDeviceCaps(desktopDc, LOGPIXELSY);
+
+    float scaleFactor = horizontalDPI / 96.0f;
+    LOGD("Native DPI: %dx%d, scaleFactor=%.3f",
+        horizontalDPI, verticalDPI, scaleFactor);
+    return scaleFactor;
+}
+
 
 /*
  * ===========================================================================

util/Util.h

@@ -199,6 +199,13 @@ bool IsWin9x(void);
  */
 void CheckedLoadString(CString* pString, UINT nID);
 
+/*
+ * Returns the desktop scaling factor (usually 1.0).  Assumes vertical and
+ * horizontal scaling is identical.
+ */
+float GetDesktopScaleFactor();
+
+
 /*
  * ====================================
  *      Miscellaneous functions