game.ui.pointer

What is under the cursor, asked cheaply.

local Pointer = require("game.ui.pointer")

local moved, x, y = Pointer.moved("table")
if moved then
    local id, index = Pointer.find(x, y, "^gp%-card%-(%d+)$")
    if index then focus(tonumber(index)) end
end

• Pointer.moved(key) -> moved, x, y — has the cursor moved since this key last asked. Reads the cursor position out of the input state, cached once a frame and shared between callers. No hit test happens here, so a frame with a resting cursor costs a few hundredths of a millisecond. The first ask for a key answers true, so a row already under a resting cursor lights on the frame its screen comes up.
• Pointer.forget(key) — make the next moved(key) answer true anyway. What sits under a resting cursor changes when the screen under it does: a new hand is dealt, a card is played, a set of rows is rebuilt. The caller says so with this.
• Pointer.idsAt(x, y) -> { string } — the widget ids under a point, top-most first. This is the expensive half (about 1.3 ms), so it is asked on the frames moved answers true for and no others.
• Pointer.find(x, y, pattern) -> id, capture — the first id under the point that matches a Lua pattern, plus that pattern's first capture.
• Pointer.at() -> x, y — the cursor, without disturbing any key's mark.

On a touchscreen and on a pad the cursor never moves, so moved answers false forever and nothing here costs anything — which is right, because hover means nothing to a finger or a thumbstick. Taps and pad focus reach the table and the cards by their own routes.