Bug 1807825 Comment 13 Edit History

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Original comment by
on 
So the source of this issue appears to be that we get an [incorrect backing scale factor of 1.0f instead of 2.0f to compute `deskBounds`](https://searchfox.org/mozilla-central/source/widget/nsBaseWidget.cpp#2012). This is because we appear to be using an instance of `PuppetWidget` to obtain the backing scale factor. This is confirmed by the following stack, which shows that we're using the base implementation `nsBaseWidget::GetWidgetScreen` instead of one of the platform overrides, such as `nsCocoaWindow::GetDesktopToDeviceScale` or `nsChildView::GetDesktopToDeviceScale`.

``
0   libmozglue.dylib              	       0x1005f7ebc mozalloc_abort + 68
1   libmozglue.dylib              	       0x1005f7ea8 mozalloc_abort + 48
2   libmozglue.dylib              	       0x1005f7ed8 abort + 20
3   XUL                           	       0x11204d32c nsBaseWidget::GetWidgetScreen() + 456
4   XUL                           	       0x10fee4b98 nsDeviceContext::ComputeFullAreaUsingScreen(nsRect*) + 80
5   XUL                           	       0x10fee4c78 nsDeviceContext::GetRect(nsRect&) + 44
6   XUL                           	       0x110495528 nsScreen::GetRect(mozilla::gfx::IntRectTyped<mozilla::CSSPixel>&) + 396
7   XUL                           	       0x11096184c mozilla::dom::Screen_Binding::get_top(JSContext*, JS::Handle<JSObject*>, void*, JSJitGetterCallArgs) + 184
8   XUL                           	       0x110eaaa1c bool mozilla::dom::binding_detail::GenericGetter<mozilla::dom::binding_detail::NormalThisPolicy, mozilla::dom::binding_detail::ThrowExceptions>(JSContext*, unsigned int, JS::Value*) + 264
9   XUL                           	       0x1134293bc js::InternalCallOrConstruct(JSContext*, JS::CallArgs const&, js::MaybeConstruct, js::CallReason) + 608
10  XUL                           	       0x113429c04 js::Call(JSContext*, JS::Handle<JS::Value>, JS::Handle<JS::Value>, js::AnyInvokeArgs const&, JS::MutableHandle<JS::Value>, js::CallReason) + 244
11  XUL                           	       0x11370c5d8 js::DebuggerObject::call(JSContext*, JS::Handle<js::DebuggerObject*>, JS::Handle<JS::Value>, JS::Handle<JS::GCVector<JS::Value, 0ul, js::TempAllocPolicy> >) + 1100
12  XUL                           	       0x11370bfb0 js::DebuggerObject::CallData::callMethod() + 336
13  XUL                           	       0x113715a24 bool js::DebuggerObject::CallData::ToNative<&(js::DebuggerObject::CallData::callMethod())>(JSContext*, unsigned int, JS::Value*) + 384
[...]
``
It isn't clear to me right now why we'd be using a `PuppetWidget` here. The only other widget implementation using the base implementation of `GetDesktopToDeviceScale` is `HeadlessWidget`.
Revision 1 by
on 
So the source of this issue appears to be that we get an [incorrect backing scale factor of 1.0f instead of 2.0f to compute `deskBounds`](https://searchfox.org/mozilla-central/source/widget/nsBaseWidget.cpp#2012). This is because we appear to be using an instance of `PuppetWidget` to obtain the backing scale factor. This is confirmed by the following stack, which shows that we're using the base implementation `nsBaseWidget::GetWidgetScreen` instead of one of the platform overrides, such as `nsCocoaWindow::GetDesktopToDeviceScale` or `nsChildView::GetDesktopToDeviceScale`.


``
0   libmozglue.dylib              	       0x1005f7ebc mozalloc_abort + 68
1   libmozglue.dylib              	       0x1005f7ea8 mozalloc_abort + 48
2   libmozglue.dylib              	       0x1005f7ed8 abort + 20
3   XUL                           	       0x11204d32c nsBaseWidget::GetWidgetScreen() + 456
4   XUL                           	       0x10fee4b98 nsDeviceContext::ComputeFullAreaUsingScreen(nsRect*) + 80
5   XUL                           	       0x10fee4c78 nsDeviceContext::GetRect(nsRect&) + 44
6   XUL                           	       0x110495528 nsScreen::GetRect(mozilla::gfx::IntRectTyped<mozilla::CSSPixel>&) + 396
7   XUL                           	       0x11096184c mozilla::dom::Screen_Binding::get_top(JSContext*, JS::Handle<JSObject*>, void*, JSJitGetterCallArgs) + 184
8   XUL                           	       0x110eaaa1c bool mozilla::dom::binding_detail::GenericGetter<mozilla::dom::binding_detail::NormalThisPolicy, mozilla::dom::binding_detail::ThrowExceptions>(JSContext*, unsigned int, JS::Value*) + 264
9   XUL                           	       0x1134293bc js::InternalCallOrConstruct(JSContext*, JS::CallArgs const&, js::MaybeConstruct, js::CallReason) + 608
10  XUL                           	       0x113429c04 js::Call(JSContext*, JS::Handle<JS::Value>, JS::Handle<JS::Value>, js::AnyInvokeArgs const&, JS::MutableHandle<JS::Value>, js::CallReason) + 244
11  XUL                           	       0x11370c5d8 js::DebuggerObject::call(JSContext*, JS::Handle<js::DebuggerObject*>, JS::Handle<JS::Value>, JS::Handle<JS::GCVector<JS::Value, 0ul, js::TempAllocPolicy> >) + 1100
12  XUL                           	       0x11370bfb0 js::DebuggerObject::CallData::callMethod() + 336
13  XUL                           	       0x113715a24 bool js::DebuggerObject::CallData::ToNative<&(js::DebuggerObject::CallData::callMethod())>(JSContext*, unsigned int, JS::Value*) + 384
[...]
``


It isn't clear to me right now why we'd be using a `PuppetWidget` here. The only other widget implementation using the base implementation of `GetDesktopToDeviceScale` is `HeadlessWidget`.
Revision 2 by
on 
So the source of this issue appears to be that we get an [incorrect backing scale factor of 1.0f instead of 2.0f to compute `deskBounds`](https://searchfox.org/mozilla-central/source/widget/nsBaseWidget.cpp#2012). This is because we appear to be using an instance of `PuppetWidget` to obtain the backing scale factor. This is confirmed by the following stack, which shows that we're using the base implementation `nsBaseWidget::GetWidgetScreen` instead of one of the platform overrides, such as `nsCocoaWindow::GetDesktopToDeviceScale` or `nsChildView::GetDesktopToDeviceScale`.


```
0   libmozglue.dylib              	       0x1005f7ebc mozalloc_abort + 68
1   libmozglue.dylib              	       0x1005f7ea8 mozalloc_abort + 48
2   libmozglue.dylib              	       0x1005f7ed8 abort + 20
3   XUL                           	       0x11204d32c nsBaseWidget::GetWidgetScreen() + 456
4   XUL                           	       0x10fee4b98 nsDeviceContext::ComputeFullAreaUsingScreen(nsRect*) + 80
5   XUL                           	       0x10fee4c78 nsDeviceContext::GetRect(nsRect&) + 44
6   XUL                           	       0x110495528 nsScreen::GetRect(mozilla::gfx::IntRectTyped<mozilla::CSSPixel>&) + 396
7   XUL                           	       0x11096184c mozilla::dom::Screen_Binding::get_top(JSContext*, JS::Handle<JSObject*>, void*, JSJitGetterCallArgs) + 184
8   XUL                           	       0x110eaaa1c bool mozilla::dom::binding_detail::GenericGetter<mozilla::dom::binding_detail::NormalThisPolicy, mozilla::dom::binding_detail::ThrowExceptions>(JSContext*, unsigned int, JS::Value*) + 264
9   XUL                           	       0x1134293bc js::InternalCallOrConstruct(JSContext*, JS::CallArgs const&, js::MaybeConstruct, js::CallReason) + 608
10  XUL                           	       0x113429c04 js::Call(JSContext*, JS::Handle<JS::Value>, JS::Handle<JS::Value>, js::AnyInvokeArgs const&, JS::MutableHandle<JS::Value>, js::CallReason) + 244
11  XUL                           	       0x11370c5d8 js::DebuggerObject::call(JSContext*, JS::Handle<js::DebuggerObject*>, JS::Handle<JS::Value>, JS::Handle<JS::GCVector<JS::Value, 0ul, js::TempAllocPolicy> >) + 1100
12  XUL                           	       0x11370bfb0 js::DebuggerObject::CallData::callMethod() + 336
13  XUL                           	       0x113715a24 bool js::DebuggerObject::CallData::ToNative<&(js::DebuggerObject::CallData::callMethod())>(JSContext*, unsigned int, JS::Value*) + 384
[...]
```


It isn't clear to me right now why we'd be using a `PuppetWidget` here. The only other widget implementation using the base implementation of `GetDesktopToDeviceScale` is `HeadlessWidget`.

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