Function measure_text_system 

pub fn measure_text_system(
    fonts: Res<'_, Assets<Font>>,
    text_query: Query<'_, '_, (Entity, Ref<'_, TextLayout>, &mut ContentSize, &mut TextNodeFlags, &mut ComputedTextBlock, Ref<'_, ComputedUiRenderTargetInfo>, &ComputedNode), With<Node>>,
    text_reader: TextReader<'_, '_, Text>,
    text_pipeline: ResMut<'_, TextPipeline>,
    font_system: ResMut<'_, CosmicFontSystem>,
)

Generates a new Measure for a text node on changes to its Text component.

A Measure is used by the UI’s layout algorithm to determine the appropriate amount of space to provide for the text given the fonts, the text itself and the constraints of the layout.

• Measures are regenerated on changes to either ComputedTextBlock or ComputedUiRenderTargetInfo.
• Changes that only modify the colors of a Text do not require a new Measure. This system is only able to detect that a Text component has changed and will regenerate the Measure on color changes. This can be expensive, particularly for large blocks of text, and the bypass_change_detection method should be called when only changing the Text’s colors.