Trellis / small multiples
Tile a grid of mini sub-plots — one chart per category in a row / column / grid layout. Tufte's small multiples.
Public surface
use wisp_chart::multi::{Trellis, TrellisCell};
// 1. Decide grid dimensions.
let trellis = Trellis::new(2, 3, Vec::new());
let cell_viewport = trellis.cell_viewport_px(Vec2::new(600.0, 360.0));
// 2. Build per-cell Graphics at `cell_viewport` sizing.
let mut cells = Vec::new();
for label in ["Q1", "Q2", "Q3", "Q4", "Q5", "Q6"] {
let plot = Plot::new(fixture_for(label))
.axes(false)
.mark(Mark::Bar { value_labels: false })
.encode(plot::x("category", ScaleKind::Band))
.encode(plot::y("value", ScaleKind::Linear));
let g = plot.render(&theme, cell_viewport);
cells.push(TrellisCell::new(label, g));
}
let trellis = Trellis::new(2, 3, cells);
// 3. Add positioned cells to the stage:
for g in trellis.positioned_cells(Vec2::new(600.0, 360.0)) {
stage.add_child(root, g);
}
// 4. Add grid borders as a separate Graphics:
let borders = trellis.emit_grid_borders(&theme, Vec2::new(600.0, 360.0));
stage.add_child(root, borders);Why v1 takes pre-built Graphics
A "true" faceting API would re-build each sub-chart from a filtered slice of the source DataFrame. That requires the chart to expose its render path through an interface — which is specific per chart family. v1 takes the simpler "caller builds the cell, we just tile" approach. The caller can use any chart type (bar / scatter / line / etc.) for each cell.
Cell sizing
The cell's Graphics must be built using
trellis.cell_viewport_px(outer) as its viewport so its NDC
range maps cleanly onto the cell rectangle. positioned_cells
applies translation + scale; if the cell was built against the
wrong viewport its content will be off-centre or clipped.