Struct BackbufferBand 

pub struct BackbufferBand {
    pub overscan_top: f64,
    pub overscan_bottom: f64,
    pub blit_dy: f64,
    pub dirty_strip_y: Option<(f64, f64)>,
}

Over-scan band request for a scrolling backbuffered widget.

Returned by crate::widget::Widget::backbuffer_band. It lets a widget (today only crate::widgets::TextArea) raster a band of content taller than its own viewport — the visible rect plus an extra overscan_top above and overscan_bottom below — so that ordinary scrolling within the band becomes a pure blit-offset change instead of a full backbuffer re-raster.

Contract

• Units. overscan_top / overscan_bottom are extra logical pixels of content rastered above / below the widget bounds. blit_dy is the vertical blit offset in logical pixels (positive shifts the band’s content up in Y-up, revealing lower content). The band is anchored in content space by the widget; blit_dy is the residual between the live scroll offset and the anchor the band was rastered at.
• Quantization. The framework quantizes both the overscan extents and blit_dy to whole physical pixels before sizing the buffer, translating the raster, and translating the blit — so the LCD subpixel structure is never resampled. The widget may pass raw (unquantized) logical values.
• Who clips. The framework clips the band blit to the widget’s bounds on every backend, so the over-scan margins never paint over sibling widgets. The widget is responsible for painting opaque content across the whole band (including the over-scan margins) so no gap shows through as the band is scrolled, and for painting any fixed chrome (border) in paint_overlay so it does not scroll with the band.
• Invalidation. The widget must keep the band’s anchor (and hence the rastered content) out of its backbuffer-cache signature, so scrolling within the band does not invalidate the cache. It must re-anchor and invalidate only when the live offset leaves the band (or the size / content / style changes).

Returning None (the default) opts out entirely and keeps the byte-for-byte original bounds-sized raster + 1:1 blit path.

Fields

overscan_top: f64

Extra logical pixels of content rastered above the widget’s top edge.

overscan_bottom: f64

Extra logical pixels of content rastered below the widget’s bottom edge.

blit_dy: f64

Vertical blit offset in logical pixels (live offset − band anchor). Positive shifts the band content up (Y-up), revealing lower content.

dirty_strip_y: Option<(f64, f64)>

Widget-local Y-up logical (lo, hi) extent of the rows the widget will repaint if the framework grants a partial (partial_allowed) re-raster this paint. None means a granted partial would still repaint the whole band (no confined strip). The framework uses this to limit the top-down plane update to exactly those rows, so it must cover byte-for-byte the same extent the widget fills and clips during its strip repaint.

Trait Implementations

impl Clone for BackbufferBand

fn clone(&self) -> BackbufferBand

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for BackbufferBand

impl Debug for BackbufferBand

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl PartialEq for BackbufferBand

fn eq(&self, other: &BackbufferBand) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for BackbufferBand