mozilla::layers::ZoomConstraints
ComputeZoomConstraintsFromViewportInfo(const nsViewportInfo& aViewportInfo)
{
mozilla::layers::ZoomConstraints constraints;
constraints.mAllowZoom = aViewportInfo.IsZoomAllowed() && gfxPrefs::APZAllowZooming();
constraints.mAllowDoubleTapZoom = constraints.mAllowZoom;
if (constraints.mAllowZoom) {
constraints.mMinZoom.scale = aViewportInfo.GetMinZoom().scale;
constraints.mMaxZoom.scale = aViewportInfo.GetMaxZoom().scale;
} else {
constraints.mMinZoom.scale = aViewportInfo.GetDefaultZoom().scale;
constraints.mMaxZoom.scale = aViewportInfo.GetDefaultZoom().scale;
}
return constraints;
}
CSSToScreenScale
MobileViewportManager::UpdateResolution(const nsViewportInfo& aViewportInfo,
const ScreenIntSize& aDisplaySize,
const CSSSize& aViewport,
const Maybe<float>& aDisplayWidthChangeRatio)
{
CSSToLayoutDeviceScale cssToDev =
mPresShell->GetPresContext()->CSSToDevPixelScale();
LayoutDeviceToLayerScale res(mPresShell->GetResolution());
if (mIsFirstPaint) {
CSSToScreenScale defaultZoom;
if (mRestoreResolution) {
defaultZoom = CSSToScreenScale(mRestoreResolution.value() * cssToDev.scale);
MVM_LOG("%p: restored zoom is %f\n", this, defaultZoom.scale);
defaultZoom = ClampZoom(defaultZoom, aViewportInfo);
} else {
defaultZoom = aViewportInfo.GetDefaultZoom();
MVM_LOG("%p: default zoom from viewport is %f\n", this, defaultZoom.scale);
if (!aViewportInfo.IsDefaultZoomValid()) {
defaultZoom = MaxScaleRatio(ScreenSize(aDisplaySize), aViewport);
MVM_LOG("%p: Intrinsic computed zoom is %f\n", this, defaultZoom.scale);
defaultZoom = ClampZoom(defaultZoom, aViewportInfo);
}
}
MOZ_ASSERT(aViewportInfo.GetMinZoom() <= defaultZoom &&
defaultZoom <= aViewportInfo.GetMaxZoom());
CSSToParentLayerScale zoom = ViewTargetAs<ParentLayerPixel>(defaultZoom,
PixelCastJustification::ScreenIsParentLayerForRoot);
LayoutDeviceToLayerScale resolution = zoom / cssToDev * ParentLayerToLayerScale(1);
MVM_LOG("%p: setting resolution %f\n", this, resolution.scale);
mPresShell->SetResolutionAndScaleTo(resolution.scale);
return defaultZoom;
}
// If this is not a first paint, then in some cases we want to update the pre-
// existing resolution so as to maintain how much actual content is visible
// within the display width. Note that "actual content" may be different with
// respect to CSS pixels because of the CSS viewport size changing.
//
// aDisplayWidthChangeRatio is non-empty if:
// (a) The meta-viewport tag information changes, and so the CSS viewport
// might change as a result. If this happens after the content has been
// painted, we want to adjust the zoom to compensate. OR
// (b) The display size changed from a nonzero value to another nonzero value.
// This covers the case where e.g. the device was rotated, and again we
// want to adjust the zoom to compensate.
// Note in particular that aDisplayWidthChangeRatio will be None if all that
// happened was a change in the full-zoom. In this case, we still want to
// compute a new CSS viewport, but we don't want to update the resolution.
//
// Given the above, the algorithm below accounts for all types of changes I
// can conceive of:
// 1. screen size changes, CSS viewport does not (pages with no meta viewport
// or a fixed size viewport)
// 2. screen size changes, CSS viewport also does (pages with a device-width
// viewport)
// 3. screen size remains constant, but CSS viewport changes (meta viewport
// tag is added or removed)
// 4. neither screen size nor CSS viewport changes
if (aDisplayWidthChangeRatio) {
float cssViewportChangeRatio = (mMobileViewportSize.width == 0)
? 1.0f : aViewport.width / mMobileViewportSize.width;
LayoutDeviceToLayerScale newRes(res.scale * aDisplayWidthChangeRatio.value()
/ cssViewportChangeRatio);
MVM_LOG("%p: Old resolution was %f, changed by %f/%f to %f\n", this, res.scale,
aDisplayWidthChangeRatio.value(), cssViewportChangeRatio, newRes.scale);
mPresShell->SetResolutionAndScaleTo(newRes.scale);
res = newRes;
}
return ViewTargetAs<ScreenPixel>(cssToDev * res / ParentLayerToLayerScale(1),
PixelCastJustification::ScreenIsParentLayerForRoot);
}