js: Move much of the handling of device pixel ratios to the mid-end

Now that the mid-end knows how to do it, we can remove some complexity
from the front end.

emcc.c

@@ -82,7 +82,6 @@ extern void js_canvas_copy_from_blitter(int id, int x, int y, int w, int h);
 extern void js_canvas_make_statusbar(void);
 extern void js_canvas_set_statusbar(const char *text);
 extern void js_canvas_set_size(int w, int h);
-extern void js_canvas_set_nominal_size();
 extern double js_get_device_pixel_ratio();
 
 extern void js_dialog_init(const char *title);
@@ -185,41 +184,30 @@ void timer_callback(double tplus)
 static int canvas_w, canvas_h;
 
 /*
- * Called when we resize as a result of changing puzzle settings.
+ * Called when we resize as a result of changing puzzle settings
- * "initial" is true if this is the first call, or the first call
+ * or device pixel ratio.
- * since a midend_reset_tilesize().  In that case, we might want to
- * adjust the size to compensate for the device pixel ratio.
  */
-static void resize(bool initial)
+static void resize()
 {
     int w, h;
-    double dpr;
     w = h = INT_MAX;
-    midend_size(me, &w, &h, false, 1.0);
+    midend_size(me, &w, &h, false, js_get_device_pixel_ratio());
-    if (initial) {
-        dpr = js_get_device_pixel_ratio();
-        if (dpr != 1.0) {
-            /*
-             * The default w and h are probably in units of
-             * sensible-sized pixels (~0.25 mm).  Scale them to the
-             * actual device pixels and then ask for a size near
-             * that.
-             */
-            w *= dpr;
-            h *= dpr;
-            midend_size(me, &w, &h, true, 1.0);
-        }
-    }
     js_canvas_set_size(w, h);
-    js_canvas_set_nominal_size();
     canvas_w = w;
     canvas_h = h;
 }
 
 /* Called from JS when the device pixel ratio changes */
-void rescale_puzzle(int w, int h)
+void rescale_puzzle()
 {
-    midend_size(me, &w, &h, true, 1.0);
+    resize();
+    midend_force_redraw(me);
+}
+
+/* Called from JS when the user uses the resize handle */
+void resize_puzzle(int w, int h)
+{
+    midend_size(me, &w, &h, true, js_get_device_pixel_ratio());
     if (canvas_w != w || canvas_h != h) { 
         js_canvas_set_size(w, h);
         canvas_w = w;
@@ -228,18 +216,11 @@ void rescale_puzzle(int w, int h)
     }
 }
 
-/* Called from JS when the user uses the resize handle */
-void resize_puzzle(int w, int h)
-{
-    rescale_puzzle(w, h);
-    js_canvas_set_nominal_size();
-}
-
 /* Called from JS when the user uses the restore button */
 void restore_puzzle_size(int w, int h)
 {
     midend_reset_tilesize(me);
-    resize(true);
+    resize();
     midend_force_redraw(me);
 }
 
@@ -734,7 +715,7 @@ static void cfg_end(bool use_results)
              */
             select_appropriate_preset();
             midend_new_game(me);
-            resize(false);
+            resize();
             midend_redraw(me);
             free_cfg(cfg);
             js_dialog_cleanup();
@@ -791,7 +772,7 @@ void command(int n)
                 assert(i < npresets);
                 midend_set_params(me, presets[i]);
                 midend_new_game(me);
-                resize(false);
+                resize();
                 midend_redraw(me);
                 update_undo_redo();
                 js_focus_canvas();
@@ -915,7 +896,7 @@ void load_game(const char *buffer, int len)
         js_error_box(err);
     } else {
         select_appropriate_preset();
-        resize(false);
+        resize();
         midend_redraw(me);
         update_permalinks();
         update_undo_redo();
@@ -957,7 +938,7 @@ int main(int argc, char **argv)
      * canvas size appropriately.
      */
     midend_new_game(me);
-    resize(true);
+    resize();
 
     /*
      * Create a status bar, if needed.

emcclib.js

@@ -558,22 +558,6 @@ mergeInto(LibraryManager.library, {
         offscreen_canvas.height = h;
     },
 
-    /*
-     * void js_canvas_set_nominal_size();
-     *
-     * Set the nominal size of the puzzle to the current canvas size
-     * scaled to CSS pixels.  This should be called whenever the
-     * canvas size is changed other than in response to a change of
-     * device pixel ratio.  This nominal size will then be used at
-     * every change of device pixel ratio to calculate the new
-     * physical size of the canvas.
-     */
-    js_canvas_set_nominal_size: function() {
-        var dpr = window.devicePixelRatio || 1;
-        nominal_width = onscreen_canvas.width / dpr;
-        nominal_height = onscreen_canvas.height / dpr;
-    },
-
     /*
      * double js_get_device_pixel_ratio();
      *

emccpre.js

@@ -30,12 +30,6 @@ var ctx;
 // by js_canvas_end_draw.
 var update_xmin, update_xmax, update_ymin, update_ymax;
 
-// Nominal size of the canvas in CSS pixels.  This is set when the
-// canvas is explicitly resized, and used as the basis of calls to
-// midend_size whenever the device pixel ratio changes.  That way
-// changes of zoom levels in browsers will generally be reversible.
-var nominal_width, nominal_height;
-
 // Module object for Emscripten. We fill in these parameters to ensure
 // that Module.run() won't be called until we're ready (we want to do
 // our own init stuff first), and that when main() returns nothing
@@ -540,8 +534,7 @@ function initPuzzle() {
      * <https://developer.mozilla.org/en-US/docs/Web/API/Window/
      * devicePixelRatio> (CC0) to work on older browsers.
      */
-    var rescale_puzzle = Module.cwrap('rescale_puzzle',
+    var rescale_puzzle = Module.cwrap('rescale_puzzle', 'void', []);
-                                      'void', ['number', 'number']);
     var mql = null;
     var update_pixel_ratio = function() {
         var dpr = window.devicePixelRatio;
@@ -549,7 +542,7 @@ function initPuzzle() {
             mql.removeListener(update_pixel_ratio);
         mql = window.matchMedia(`(resolution: ${dpr}dppx)`);
         mql.addListener(update_pixel_ratio);
-        rescale_puzzle(nominal_width * dpr, nominal_height * dpr);
+        rescale_puzzle();
     }
 
     Module.onRuntimeInitialized = function() {