layout

type Chart struct {
	// Canvas is the full drawing surface.
	Canvas ir.Rect
	// Theme supplies sizes, paddings and fonts.
	Theme theme.Theme

	// Title is the chart title, or "" for none.
	Title string
	// XTitle and YTitle are axis titles, or "" for none.
	XTitle, YTitle string

	// XLabels and YLabels are the tick label texts. Only their measured
	// extents matter here; their positions are the scales' business.
	XLabels, YLabels []string

	// LegendLabels are the series names. An empty slice suppresses the legend.
	LegendLabels []string

	// Colorbars are the continuous colour guides. Only the extents of their
	// titles and tick labels matter here; where the ticks fall is the colour
	// scale's business, and it needs the bar's rectangle to answer.
	Colorbars []Colorbar
}

type Colorbar struct {
	// Title names the quantity the ramp encodes, or "" for none.
	Title string
	// Ticks are the labels written beside the bar.
	Ticks []string
}

type Grid struct {
	// Canvas is the full drawing surface.
	Canvas ir.Rect
	// Theme supplies sizes, paddings and fonts.
	Theme theme.Theme

	// Title is the chart title above the whole grid, or "" for none.
	Title string
	// XTitle and YTitle label the shared axes, once for the grid.
	XTitle, YTitle string

	// Rows and Cols are the shape of the grid.
	Rows, Cols int

	// Panels are the panels, in any order. A cell with no panel is a hole.
	Panels []Panel

	// LegendLabels and Colorbars are the guides for the grid as a whole.
	LegendLabels []string
	Colorbars    []Colorbar
}

type GridResult struct {
	// Areas are the panel rectangles, parallel to Grid.Panels.
	Areas []ir.Rect
	// Strips are the label bands above each panel, parallel to Grid.Panels
	// and empty for a panel with no strip.
	Strips []ir.Rect
	// RightStrips are the label bands beside each panel, parallel to
	// Grid.Panels and empty for a panel with none.
	RightStrips []ir.Rect

	// Region is the rectangle the panels and their gutters occupy together.
	// The chart title is centred on it and the guides sit beside it.
	Region ir.Rect

	// Title, XTitle and YTitle are the baseline anchors for the grid's own
	// titles, zero when there is none. YTitle is drawn rotated a quarter turn
	// anticlockwise.
	Title, XTitle, YTitle ir.Point

	// Legend and Colorbars are the guide boxes, as in [Result].
	Legend    ir.Rect
	Colorbars []ir.Rect

	// TickLabelPad is copied from the theme so the renderer does not re-derive
	// it.
	TickLabelPad float32
}

type Measurer interface {
	Measure(run ir.TextRun) ir.TextMetrics
}

type Panel struct {
	// Row and Col place the panel.
	Row, Col int

	// Strip is the label written in a band above the panel, or "" for none.
	// It is what a facet is named by.
	Strip string
	// RightStrip is a label written in a band down the panel's right side,
	// reading top to bottom. A two-way facet names its rows this way.
	RightStrip string

	// XLabels and YLabels are the tick labels this panel writes. A panel that
	// shares an axis with the panel beside it leaves them empty and takes the
	// space anyway, so that the panels stay the same size.
	XLabels, YLabels []string
}

type Result struct {
	// Plot is the data area. Scales map into it.
	Plot ir.Rect
	// Title is the baseline anchor for the chart title, horizontally centred
	// on the plot area. Zero if there is no title.
	Title ir.Point
	// XTitle is the baseline anchor for the X axis title, centred on the plot
	// area. Zero if there is none.
	XTitle ir.Point
	// YTitle is the anchor for the Y axis title, centred on the plot area and
	// meant to be drawn rotated a quarter turn anticlockwise. Zero if there is
	// none.
	YTitle ir.Point
	// Legend is the rectangle reserved for the legend, empty if there is none.
	Legend ir.Rect
	// Colorbars are the rectangles reserved for the colour guides, one per
	// entry in Chart.Colorbars and in the same order. Each covers the bar, its
	// tick labels and its title.
	Colorbars []ir.Rect
	// TickLabelPad is the distance from the axis to the near edge of a tick
	// label, copied from the theme so the renderer does not re-derive it.
	TickLabelPad float32
}