commit 4b95a904d81753b73c6ed24f65b5ff2ee84e97e2
Author: David Barton <db9052@sourceforge.net>
Date:   Mon Sep 4 06:27:12 2017 +0200

    Preserve aspect ratio when resizing

    To make the image patch even more useful, I've written this patch to
    allow the aspect ratio to be preserved when resizing selections. (It
    doesn't just apply to images.) Simply resize using the right mouse
    button (button-3) rather than the left mouse button.

    This patch should be applied after the enhanced image patch. (Though
    it'd be easy enough to make the changes to the raw 0.4.5 source directly
    since it doesn't change any of the image patch related areas.)

diff --git a/src/xo-selection.c b/src/xo-selection.c
index 7359bd8..05132b4 100644
--- a/src/xo-selection.c
+++ b/src/xo-selection.c
@@ -347,6 +347,12 @@ gboolean start_resizesel(GdkEvent *event)
     ui.selection->new_x2 = ui.selection->bbox.right;
     gnome_canvas_item_set(ui.selection->canvas_item, "dash", NULL, NULL);
     update_cursor_for_resize(pt);
+
+    // Check whether we should preserve the aspect ratio
+    if (event->button.button == 3)
+        ui.cur_brush->tool_options |= TOOLOPT_SELECT_PRESERVE;
+    else
+        ui.cur_brush->tool_options &= ~TOOLOPT_SELECT_PRESERVE;
     return TRUE;
   }
   return FALSE;
@@ -498,6 +504,38 @@ void continue_resizesel(GdkEvent *event)
   if (ui.selection->resizing_left) ui.selection->new_x1 = pt[0];
   if (ui.selection->resizing_right) ui.selection->new_x2 = pt[0];
 
+  if (ui.cur_brush->tool_options & TOOLOPT_SELECT_PRESERVE) {
+	  double aspectratio = (ui.selection->bbox.top - ui.selection->bbox.bottom)/(ui.selection->bbox.right - ui.selection->bbox.left);
+	  double newheight = ui.selection->new_y1 - ui.selection->new_y2;
+	  double newwidth = ui.selection->new_x2 - ui.selection->new_x1;
+	  gboolean boundheight;
+
+	  // Resizing from top or bottom only
+	  if ((ui.selection->resizing_top || ui.selection->resizing_bottom) && !(ui.selection->resizing_left || ui.selection->resizing_right))
+		  boundheight = 0;
+	  // Resizing from right or left only
+	  else if (!(ui.selection->resizing_top || ui.selection->resizing_bottom) && (ui.selection->resizing_left || ui.selection->resizing_right))
+		  boundheight = 1;
+	  // Resizing from a corner
+	  else if (newheight/aspectratio > newwidth)
+		  boundheight = 0;
+	  else
+		  boundheight = 1;
+
+	  if (boundheight) {
+		  // Bound the height
+		  newheight = newwidth*aspectratio;
+		  if (ui.selection->resizing_top) ui.selection->new_y1 = ui.selection->new_y2 + newheight;
+		  else ui.selection->new_y2 = ui.selection->new_y1 - newheight;
+	  }
+	  else {
+		  // Bound the width
+		  newwidth = newheight/aspectratio;
+		  if (ui.selection->resizing_left) ui.selection->new_x1 = ui.selection->new_x2 - newwidth;
+		  else ui.selection->new_x2 = ui.selection->new_x1 + newwidth;
+	  }
+  }
+
   gnome_canvas_item_set(ui.selection->canvas_item, 
     "x1", ui.selection->new_x1, "x2", ui.selection->new_x2,
     "y1", ui.selection->new_y1, "y2", ui.selection->new_y2, NULL);
diff --git a/src/xournal.h b/src/xournal.h
index 3599e77..e8ad4ed 100644
--- a/src/xournal.h
+++ b/src/xournal.h
@@ -160,6 +160,7 @@ extern guint predef_bgcolors_rgba[COLOR_MAX];
 #define TOOLOPT_ERASER_STANDARD     0
 #define TOOLOPT_ERASER_WHITEOUT     1
 #define TOOLOPT_ERASER_STROKES      2
+#define TOOLOPT_SELECT_PRESERVE     1 // Preserve the aspect ratio of the selection when resizing
 
 extern double predef_thickness[NUM_STROKE_TOOLS][THICKNESS_MAX];