Geometry for the evaluation graph

The arithmetic behind the graph, with no drawing: where each point sits and what shapes join them. eval_graph_svg() turns this into an SVG. They are split so this layer stays free of any UI toolkit - see the note in test-core-boundary.R.

Usage

eval_graph_geometry(cp, width = 420, height = 110)

Arguments

cp

Centipawn evaluations from White's point of view, one per position (so one more than the number of moves). NA where not yet measured.

width, height

Pixel size of the graph.

Value

A list with n points, xs/ys coordinates, points and area as SVG coordinate strings, mid (the halfway line) and hit_width (the width of one clickable band); or NULL if there is nothing to draw.

Details

Evaluations are squashed with the same logistic the eval bar uses, so a three-pawn edge and a nine-pawn one stay visibly different without the graph being dominated by a single decisive moment.

Positions that have not been evaluated yet carry the last known value forward rather than breaking the line, so the graph does not flicker while the engine catches up with a fast game.