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ContentSize replacement fix (bevyengine#9753)
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# Objective

If you remove a `ContentSize` component from a Bevy UI entity and then
replace it `ui_layout_system` will remove the measure func from the
internal Taffy layout tree but no new measure func will be generated to
replace it since it's the widget systems that are responsible for
creating their respective measure funcs not `ui_layout_system`. The
widget systems only perform a measure func update on changes to a widget
entity's content. This means that until its content is changed in some
way, no content will be displayed by the node.

### Example

This example spawns a text node which disappears after a few moments
once its `ContentSize` component is replaced.

```rust
use bevy::prelude::*;
use bevy::ui::ContentSize;

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .add_systems(Update, delayed_replacement)
        .run();
}

fn setup(mut commands: Commands) {
    commands.spawn(Camera2dBundle::default());
    commands.spawn(
        TextBundle::from_section(
            "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.",
            TextStyle::default(),
        )
    );
}

// Waits a few frames to make sure the font is loaded and the text's glyph layout has been generated.
fn delayed_replacement(mut commands: Commands, mut count: Local<usize>, query: Query<Entity, With<Style>>) {
    *count += 1;
    if *count == 10 {
        for item in query.iter() {
            commands
                .entity(item)
                .remove::<ContentSize>()
                .insert(ContentSize::default());
        }
    }
}
```

## Solution

Perform `ui_layout_system`'s `ContentSize` removal detection and
resolution first, before the measure func updates.
Then in the widget systems, generate a new `Measure` when a
`ContentSize` component is added to a widget entity.

## Changelog

* `measure_text_system`, `update_image_content_size_system` and
`update_atlas_content_size_system` generate a new `Measure` when a
`ContentSize` component is added.
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ickshonpe authored and Ray Redondo committed Jan 9, 2024
1 parent 950cfd7 commit 1fdb7c1
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Showing 3 changed files with 15 additions and 8 deletions.
10 changes: 5 additions & 5 deletions crates/bevy_ui/src/layout/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -274,6 +274,11 @@ pub fn ui_layout_system(
}
}

// When a `ContentSize` component is removed from an entity, we need to remove the measure from the corresponding taffy node.
for entity in removed_content_sizes.read() {
ui_surface.try_remove_measure(entity);
}

for (entity, mut content_size) in measure_query.iter_mut() {
if let Some(measure_func) = content_size.measure_func.take() {
ui_surface.update_measure(entity, measure_func);
Expand All @@ -283,11 +288,6 @@ pub fn ui_layout_system(
// clean up removed nodes
ui_surface.remove_entities(removed_nodes.read());

// When a `ContentSize` component is removed from an entity, we need to remove the measure from the corresponding taffy node.
for entity in removed_content_sizes.read() {
ui_surface.try_remove_measure(entity);
}

// update window children (for now assuming all Nodes live in the primary window)
ui_surface.set_window_children(primary_window_entity, root_node_query.iter());

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11 changes: 9 additions & 2 deletions crates/bevy_ui/src/widget/image.rs
Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@ use crate::{
};
use bevy_asset::{Assets, Handle};

use bevy_ecs::change_detection::DetectChanges;
use bevy_ecs::query::Without;
use bevy_ecs::{
prelude::Component,
Expand Down Expand Up @@ -96,7 +97,10 @@ pub fn update_image_content_size_system(
texture.texture_descriptor.size.height as f32,
);
// Update only if size or scale factor has changed to avoid needless layout calculations
if size != image_size.size || combined_scale_factor != *previous_combined_scale_factor {
if size != image_size.size
|| combined_scale_factor != *previous_combined_scale_factor
|| content_size.is_added()
{
image_size.size = size;
content_size.set(ImageMeasure {
// multiply the image size by the scale factor to get the physical size
Expand Down Expand Up @@ -135,7 +139,10 @@ pub fn update_atlas_content_size_system(
if let Some(atlas) = atlases.get(atlas) {
let size = atlas.textures[atlas_image.index].size();
// Update only if size or scale factor has changed to avoid needless layout calculations
if size != image_size.size || combined_scale_factor != *previous_combined_scale_factor {
if size != image_size.size
|| combined_scale_factor != *previous_combined_scale_factor
|| content_size.is_added()
{
image_size.size = size;
content_size.set(ImageMeasure {
// multiply the image size by the scale factor to get the physical size
Expand Down
2 changes: 1 addition & 1 deletion crates/bevy_ui/src/widget/text.rs
Original file line number Diff line number Diff line change
Expand Up @@ -128,7 +128,7 @@ pub fn measure_text_system(
if *last_scale_factor == scale_factor {
// scale factor unchanged, only create new measure funcs for modified text
for (text, content_size, text_flags) in text_query.iter_mut() {
if text.is_changed() || text_flags.needs_new_measure_func {
if text.is_changed() || text_flags.needs_new_measure_func || content_size.is_added() {
create_text_measure(&fonts, scale_factor, text, content_size, text_flags);
}
}
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