Function build_text_calls 

pub fn build_text_calls(
    labels: &[TextLabel],
    loaded_fonts: &FontSet,
    win_w: f32,
    win_h: f32,
    clips: &ClipRects,
    layers: &OverlayLayers,
) -> Vec<TextDrawCall>

Build one TextDrawCall per TextLabel, laying out character quads using the loaded font metrics. When win_w and win_h are both > 0.0, labels with centered = true are repositioned to the centre of the viewport. clips maps an element id to a reference-space clip band; a label found there has its call scissored to that band (mapped to the window), so a scrollable panel’s off-band rows do not bleed over its chrome.