facebook / yoga

Yoga is an embeddable layout engine targeting web standards.
https://yogalayout.dev/
MIT License
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top position is wrong when previous item's height is 0.5, on 3x scale screen #1528

Open hanleylee opened 10 months ago

hanleylee commented 10 months ago

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Issues and Steps to Reproduce

Anyone can reproduce it using below code(YogaKit (for iOS) 2.0.1)

import Foundation
import yoga

final class YogaTestVC: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        initView()
    }
}

// MARK: UI

extension YogaTestVC {
    private func initView() {
        view.backgroundColor = .black

        view.configureLayout { layout in
            layout.isEnabled = true
            layout.flexDirection = .column
            layout.alignItems = .stretch
            layout.justifyContent = .center
        }

        let containerView = UIView()
        containerView.backgroundColor = .white
        containerView.configureLayout { layout in
            layout.isEnabled = true
            layout.flexDirection = .column
            layout.alignItems = .stretch
        }
        view.addSubview(containerView)

        let view1 = UIView()
        view1.backgroundColor = .orange
        view1.configureLayout { layout in
            layout.isEnabled = true
            layout.height = YGValue(value: 50, unit: .point)
        }
        containerView.addSubview(view1)

        let view2 = UIView()
        view2.backgroundColor = .green
        view2.configureLayout { layout in
            layout.isEnabled = true
            layout.height = 0.5
        }
        containerView.addSubview(view2)

        let view3 = UIView()
        view3.backgroundColor = .orange
        view3.configureLayout { layout in
            layout.isEnabled = true
            layout.height = 50
        }
        containerView.addSubview(view3)

        view.yoga.applyLayout(preservingOrigin: true)
    }
}

Expected Behavior

The top position of view3 is 50.667 instead of 50.333, because the heights of view1 and view2 are 50, 0.667 respectively

Actual Behavior

The top position of view3 is 50.333

Screenshot

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Explore

After check the source code, I found here will convert view3's top from 50.5 to 50.333, while textRounding is true.

https://github.com/facebook/yoga/blob/7697be57a86606e6019e4a978587ffc0e37cb84b/yoga/algorithm/PixelGrid.cpp#L84-L94

Other

I suspect this issue is similar to #901, but can't be sure

NickGerleman commented 10 months ago

Yoga assumes every leaf node is YGNodeTypeText, which triggers ceil instead of round. This assumption is not correct when measure function is used to delegate to different layout system.