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# Objective `text_system` runs before the UI layout is calculated and the size of the text node is determined, so it cannot correctly shape the text to fit the layout, and has no way of determining if the text needs to be wrapped. The function `text_constraint` attempts to determine the size of the node from the local size constraints in the `Style` component. It can't be made to work, you have to compute the whole layout to get the correct size. A simple example of where this fails completely is a text node set to stretch to fill the empty space adjacent to a node with size constraints set to `Val::Percent(50.)`. The text node will take up half the space, even though its size constraints are `Val::Auto` Also because the `text_system` queries for changes to the `Style` component, when a style value is changed that doesn't affect the node's geometry the text is recomputed unnecessarily. Querying on changes to `Node` is not much better. The UI layout is changed to fit the `CalculatedSize` of the text, so the size of the node is changed and so the text and UI layout get recalculated multiple times from a single change to a `Text`. Also, the `MeasureFunc` doesn't work at all, it doesn't have enough information to fit the text correctly and makes no attempt. Fixes #7663, #6717, #5834, #1490, ## Solution Split the `text_system` into two functions: * `measure_text_system` which calculates the size constraints for the text node and runs before `UiSystem::Flex` * `text_system` which runs after `UiSystem::Flex` and generates the actual text. * Fix the `MeasureFunc` calculations. --- Text wrapping in main: <img width="961" alt="Capturemain" src="https://user-images.githubusercontent.com/27962798/220425740-4fe4bf46-24fb-4685-a1cf-bc01e139e72d.PNG"> With this PR: <img width="961" alt="captured_wrap" src="https://user-images.githubusercontent.com/27962798/220425807-949996b0-f127-4637-9f33-56a6da944fb0.PNG"> ## Changelog * Removed the previous fields from `CalculatedSize`. `CalculatedSize` now contains a boxed `Measure`. * Added `measurement` module to `bevy_ui`. * Added the method `create_text_measure` to `TextPipeline`. * Added a new system `measure_text_system` that runs before `UiSystem::Flex` that creates a `MeasureFunc` for the text. * Rescheduled `text_system` to run after `UiSystem::Flex`. * Added a trait `Measure`. A `Measure` is used to compute the size of a UI node when the size of that node is based on its content. * Added `ImageMeasure` and `TextMeasure` which implement `Measure`. * Added a new component `UiImageSize` which is used by `update_image_calculated_size_system` to track image size changes. * Added a `UiImageSize` component to `ImageBundle`. ## Migration Guide `ImageBundle` has a new component `UiImageSize` which contains the size of the image bundle's texture and is updated automatically by `update_image_calculated_size_system` --------- Co-authored-by: François <mockersf@gmail.com> |
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