Platform: emit EmscriptenApp viewport event also on pixel ratio change.

I.e., when the page is zoomed. Until now it was only triggered when the
actual canvas was resized, which happens with the zoom only if the
canvas fills the whole window.

src/Magnum/Platform/EmscriptenApplication.cpp

@@ -305,11 +305,12 @@ bool EmscriptenApplication::tryCreate(const Configuration& configuration) {
 
     _canvasTarget = canvasId();
 
-    /* Get CSS canvas size and cache it. This is used later to detect canvas
-       resizes in emscripten_set_resize_callback() and fire viewport events,
-       because browsers are only required to fire resize events on the window
-       and not on particular DOM elements. */
+    /* Get CSS canvas size and device pixel ratio and cache it. This is used
+       later to detect canvas resizes in emscripten_set_resize_callback() and
+       fire viewport events, because browsers are only required to fire resize
+       events on the window and not on particular DOM elements. */
     _lastKnownCanvasSize = windowSize();
+    _lastKnownDevicePixelRatio = devicePixelRatio();
 
     /* By default Emscripten creates a 300x150 canvas. That's so freaking
        random I'm getting mad. Use the real (CSS pixels) canvas size instead,
@@ -330,9 +331,8 @@ bool EmscriptenApplication::tryCreate(const Configuration& configuration) {
        ratio together with DPI scaling (which is 1.0 by default) defines
        framebuffer size. See class docs for why it's done like that. */
     _configurationDpiScaling = configuration.dpiScaling();
-    const Vector2 devicePixelRatio = this->devicePixelRatio();
-    Debug{verbose} << "Platform::EmscriptenApplication: device pixel ratio" << devicePixelRatio.x();
-    const Vector2i scaledCanvasSize = canvasSize*dpiScaling(configuration)*devicePixelRatio;
+    Debug{verbose} << "Platform::EmscriptenApplication: device pixel ratio" << _lastKnownDevicePixelRatio.x();
+    const Vector2i scaledCanvasSize = canvasSize*dpiScaling(configuration)*_lastKnownDevicePixelRatio;
     emscripten_set_canvas_element_size(_canvasTarget.data(), scaledCanvasSize.x(), scaledCanvasSize.y());
 
     setupCallbacks(!!(configuration.windowFlags() & Configuration::WindowFlag::Resizable));
@@ -384,11 +384,12 @@ bool EmscriptenApplication::tryCreate(const Configuration& configuration, const
        or overridden/manually set by the user. */
     _canvasTarget = canvasId();
 
-    /* Get CSS canvas size and cache it. This is used later to detect canvas
-       resizes in emscripten_set_resize_callback() and fire viewport events,
-       because browsers are only required to fire resize events on the window
-       and not on particular DOM elements. */
+    /* Get CSS canvas size and device pixel ratio and cache it. This is used
+       later to detect canvas resizes in emscripten_set_resize_callback() and
+       fire viewport events, because browsers are only required to fire resize
+       events on the window and not on particular DOM elements. */
     _lastKnownCanvasSize = windowSize();
+    _lastKnownDevicePixelRatio = devicePixelRatio();
 
     /* By default Emscripten creates a 300x150 canvas. That's so freaking
        random I'm getting mad. Use the real (CSS pixels) canvas size instead,
@@ -409,9 +410,8 @@ bool EmscriptenApplication::tryCreate(const Configuration& configuration, const
        ratio together with DPI scaling (which is 1.0 by default) defines
        framebuffer size. See class docs for why it's done like that. */
     _configurationDpiScaling = configuration.dpiScaling();
-    const Vector2 devicePixelRatio = this->devicePixelRatio();
-    Debug{verbose} << "Platform::EmscriptenApplication: device pixel ratio" << devicePixelRatio.x();
-    const Vector2i scaledCanvasSize = canvasSize*dpiScaling(configuration)*devicePixelRatio;
+    Debug{verbose} << "Platform::EmscriptenApplication: device pixel ratio" << _lastKnownDevicePixelRatio.x();
+    const Vector2i scaledCanvasSize = canvasSize*dpiScaling(configuration)*_lastKnownDevicePixelRatio;
     emscripten_set_canvas_element_size(_canvasTarget.data(), scaledCanvasSize.x(), scaledCanvasSize.y());
 
     /* Create WebGL context */
@@ -477,10 +477,11 @@ void EmscriptenApplication::swapBuffers() {
    setContainerCssClass() */
 void EmscriptenApplication::handleCanvasResize(const EmscriptenUiEvent* event) {
     const Vector2i canvasSize{windowSize()};
-    if(canvasSize != _lastKnownCanvasSize) {
+    const Vector2 devicePixelRatio = this->devicePixelRatio();
+    if(canvasSize != _lastKnownCanvasSize || devicePixelRatio != _lastKnownDevicePixelRatio) {
         _lastKnownCanvasSize = canvasSize;
+        _lastKnownDevicePixelRatio = devicePixelRatio;
         const Vector2 dpiScaling = this->dpiScaling();
-        const Vector2 devicePixelRatio = this->devicePixelRatio();
         const Vector2i size = canvasSize*dpiScaling*devicePixelRatio;
         emscripten_set_canvas_element_size(_canvasTarget.data(), size.x(), size.y());
         ViewportEvent e{event, canvasSize,

src/Magnum/Platform/EmscriptenApplication.h

@@ -898,6 +898,7 @@ class EmscriptenApplication {
         void setupAnimationFrame(bool ForceAnimationFrame);
 
         Vector2i _lastKnownCanvasSize, _previousMouseMovePosition{-1};
+        Vector2 _lastKnownDevicePixelRatio;
 
         Flags _flags;
         Cursor _cursor = Cursor::Arrow;