Shubham Gupta 4e315eba20 paint: Use viewport meta tag's min-scale and max-scale to clamp pinch zoom (#40098)
**Note: Targeting Mobile devices only.**

Clamp Pinch Zoom factor using `viewport`' scale range parsed from
`<meta>` tag.

## **Behavior in Servo with this PR**

Zoom Type |  Device Type | Meta Supported |Range 
-- | -- | -- | -- 
Pinch Zoom |  Mobile | Yes |Parsed from <meta> 
Pinch Zoom |  Desktop | No |Default

## **Observed behavior in Chrome**:

Device Type | Viewport Meta Support (pref) | Pinch Zoom (No Reflow) |
Zoom (using keyboard)
-- | -- | -- | --
Mobile (Android) | Yes | Clamped within Viewport Meta Range | Applied to
Pinch Zoom*
Desktop (Touch Screen) | No | Clamped within Default Range | Same as
Zoom (using menu)

## References from Chromium:
- Defination of
[page_scale_delta](https://source.chromium.org/chromium/chromium/src/+/main:cc/trees/layer_tree_host_client.h;drc=56c66e417c83e2096a4e4e8a5c4ab7bbd525c9f3;bpv=1;bpt=1;l=39?gsn=page_scale_delta&gs=KYTHE%3A%2F%2Fkythe%3A%2F%2Fchromium.googlesource.com%2Fcodesearch%2Fchromium%2Fsrc%2F%2Fmain%3Flang%3Dc%252B%252B%3Fpath%3Dcc%2Ftrees%2Flayer_tree_host_client.h%23SKME3VsvfEmKrf_3d5aQckyeMEaDxgiGETVRCM1Haac);
-
[WebViewImpl::ApplyViewportChanges](https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/exported/web_view_impl.cc;drc=56c66e417c83e2096a4e4e8a5c4ab7bbd525c9f3;bpv=1;bpt=1;l=4108?gsn=ApplyViewportChanges&gs=KYTHE%3A%2F%2Fkythe%3A%2F%2Fchromium.googlesource.com%2Fcodesearch%2Fchromium%2Fsrc%2F%2Fmain%3Flang%3Dc%252B%252B%3Fpath%3Dthird_party%2Fblink%2Frenderer%2Fcore%2Fexported%2Fweb_view_impl.cc%23ll5snmeunTDzY4PwOwxyrNwNc4EI13SFfZnHIWuBsNw)
->
[SetPageScaleFactorAndLocation](https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/exported/web_view_impl.cc;drc=56c66e417c83e2096a4e4e8a5c4ab7bbd525c9f3;bpv=1;bpt=1;l=2430?gsn=SetPageScaleFactorAndLocation&gs=KYTHE%3A%2F%2Fkythe%3A%2F%2Fchromium.googlesource.com%2Fcodesearch%2Fchromium%2Fsrc%2F%2Fmain%3Flang%3Dc%252B%252B%3Fpath%3Dthird_party%2Fblink%2Frenderer%2Fcore%2Fexported%2Fweb_view_impl.cc%23wJPsxPYe-aA-buH8xy-IKLTHLqtZ_IgGsuARSYerlUE)
->
[SetScaleAndLocation](https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/frame/visual_viewport.cc;drc=56c66e417c83e2096a4e4e8a5c4ab7bbd525c9f3;bpv=1;bpt=1;l=513?gsn=SetScaleAndLocation&gs=KYTHE%3A%2F%2Fkythe%3A%2F%2Fchromium.googlesource.com%2Fcodesearch%2Fchromium%2Fsrc%2F%2Fmain%3Flang%3Dc%252B%252B%3Fpath%3Dthird_party%2Fblink%2Frenderer%2Fcore%2Fframe%2Fvisual_viewport.cc%23u-DPCmPBwcQcKi3oKJ1duPI83otfHDXzsQI8KMYusaA)
->
[DidSetScaleOrLocation](https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/frame/visual_viewport.cc;drc=56c66e417c83e2096a4e4e8a5c4ab7bbd525c9f3;bpv=1;bpt=1;l=543?gsn=DidSetScaleOrLocation&gs=KYTHE%3A%2F%2Fkythe%3A%2F%2Fchromium.googlesource.com%2Fcodesearch%2Fchromium%2Fsrc%2F%2Fmain%3Flang%3Dc%252B%252B%3Fpath%3Dthird_party%2Fblink%2Frenderer%2Fcore%2Fframe%2Fvisual_viewport.cc%23cUPTZHhvInyEDOapVOzXmCPKg9DO_tYGVZY7y0D9EBw)
->
[ClampToConstraints](https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/frame/page_scale_constraints.cc;drc=56c66e417c83e2096a4e4e8a5c4ab7bbd525c9f3;bpv=1;bpt=1;l=60?gsn=ClampToConstraints&gs=KYTHE%3A%2F%2Fkythe%3A%2F%2Fchromium.googlesource.com%2Fcodesearch%2Fchromium%2Fsrc%2F%2Fmain%3Flang%3Dc%252B%252B%3Fpath%3Dthird_party%2Fblink%2Frenderer%2Fcore%2Fframe%2Fpage_scale_constraints.cc%23hQCpRu6_p6TTaFLTpDMnO_d-g3SnRpG-p5UlazTZlK8)

Testing: New WPT Test Added:
`wpt/visual-viewport/viewport-scale-clamped.html`



Fixes: #40390 (Observed Inconsistent behavior with Chrome Android)

---------

Signed-off-by: Shubham Gupta <shubham.gupta@chromium.org>
2026-04-03 11:50:31 +00:00
2025-11-13 08:48:01 +00:00
2018-11-19 14:46:43 +01:00
2026-02-03 12:43:04 +00:00
2026-03-10 20:55:14 +00:00
2023-08-17 15:07:43 +00:00

The Servo Parallel Browser Engine Project

Servo is a prototype web browser engine written in the Rust language. It is currently developed on 64-bit macOS, 64-bit Linux, 64-bit Windows, 64-bit OpenHarmony, and Android.

Servo welcomes contribution from everyone. Check out:

Coordination of Servo development happens:

Getting started

For more detailed build instructions, see the Servo Book under Getting the Code and Building Servo.

macOS

  • Download and install Xcode and brew.
  • Install uv: curl -LsSf https://astral.sh/uv/install.sh | sh
  • Install rustup: curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
  • Restart your shell to make sure cargo is available
  • Install the other dependencies: ./mach bootstrap
  • Build servoshell: ./mach build

Linux

  • Install curl:
    • Arch: sudo pacman -S --needed curl
    • Debian, Ubuntu: sudo apt install curl
    • Fedora: sudo dnf install curl
    • Gentoo: sudo emerge net-misc/curl
  • Install uv: curl -LsSf https://astral.sh/uv/install.sh | sh
  • Install rustup: curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
  • Restart your shell to make sure cargo is available
  • Install the other dependencies: ./mach bootstrap
  • Build servoshell: ./mach build

Windows

  • Download uv, choco, and rustup
    • Be sure to select Quick install via the Visual Studio Community installer
  • In the Visual Studio Installer, ensure the following components are installed:
    • Windows 10/11 SDK (anything >= 10.0.19041.0) (Microsoft.VisualStudio.Component.Windows{10, 11}SDK.{>=19041})
    • MSVC v143 - VS 2022 C++ x64/x86 build tools (Latest) (Microsoft.VisualStudio.Component.VC.Tools.x86.x64)
    • C++ ATL for latest v143 build tools (x86 & x64) (Microsoft.VisualStudio.Component.VC.ATL)
  • Restart your shell to make sure cargo is available
  • Install the other dependencies: .\mach bootstrap
  • Build servoshell: .\mach build

Android

  • Ensure that the following environment variables are set:
    • ANDROID_SDK_ROOT
    • ANDROID_NDK_ROOT: $ANDROID_SDK_ROOT/ndk/28.2.13676358/ ANDROID_SDK_ROOT can be any directory (such as ~/android-sdk). All of the Android build dependencies will be installed there.
  • Install the latest version of the Android command-line tools to $ANDROID_SDK_ROOT/cmdline-tools/latest.
  • Run the following command to install the necessary components:
    sudo $ANDROID_SDK_ROOT/cmdline-tools/latest/bin/sdkmanager --install \
     "build-tools;34.0.0" \
     "emulator" \
     "ndk;28.2.13676358" \
     "platform-tools" \
     "platforms;android-33" \
     "system-images;android-33;google_apis;x86_64"
    
  • Follow the instructions above for the platform you are building on

OpenHarmony

  • Follow the instructions above for the platform you are building on to prepare the environment.
  • Depending on the target distribution (e.g. HarmonyOS NEXT vs pure OpenHarmony) the build configuration will differ slightly.
  • Ensure that the following environment variables are set
    • DEVECO_SDK_HOME (Required when targeting HarmonyOS NEXT)
    • OHOS_BASE_SDK_HOME (Required when targeting OpenHarmony)
    • OHOS_SDK_NATIVE (e.g. ${DEVECO_SDK_HOME}/default/openharmony/native or ${OHOS_BASE_SDK_HOME}/${API_VERSION}/native)
    • SERVO_OHOS_SIGNING_CONFIG: Path to json file containing a valid signing configuration for the demo app.
  • Review the detailed instructions at [Building for OpenHarmony].
  • The target distribution can be modified by passing --flavor=<default|harmonyos> to mach <build|package|install>.
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