Grid

A uniform lattice that divides a width × height area into square cells and reports which cells a shape covers.

The circle opts into occupancy with setGrid(), so moving it refreshes gridCells with every lattice cell its bounding box covers. Cells outside the grid are dropped rather than wrapped.

This is the spatial index behind Circ and Rect occupancy. Construct it with the area and a cell size; len is a Vec2 holding the column and row counts. Attaching it to a shape fills that shape's gridCells with the indices its bounding box overlaps.

testCells() then answers whether two shapes share a cell, a cheap broad-phase check to run before any exact collision maths. Unused and off-grid slots use the Grid.emptyCell sentinel (-1), which testCells() ignores. draw() paints the lattice for debugging.

import { Circ, Grid, Vec2 } from '@1pizzateam/spock';

const grid = new Grid(800, 600, 32);
const circle = new Circ(38, 400, 300).setGrid(grid);

circle.setPosition(new Vec2(120, 240));
const occupied = circle.gridCells.filter(cell => cell !== Grid.emptyCell);

const other = new Circ(20, 110, 96).setGrid(grid);
if (grid.testCells(circle.gridCells, other.gridCells)) {
  // close enough to be worth an exact narrow-phase test
}

Constructor

Divide width × height into cells of cellSize.

Cell counts are rounded up, so the lattice always covers the whole area even when the size is not an exact multiple of the cell size. len holds the column and row counts as a Vec2.

new Grid(width: number, height: number, cellSize: number)

Parameters

• width — number.
• height — number.
• cellSize — number.

Returns

Grid

Example

import { Grid } from '@1pizzateam/spock';

const value = new Grid(100, 100, 10);

Grid.totalCells

Total number of cells in the lattice (cols × rows).

get totalCells(): number

Returns

number

Grid.testCells()

True if the sorted occupancy lists share a real cell.

Broad-phase overlap test: true when the two occupancy lists share a cell. It ignores the Grid.emptyCell sentinel, so unused slots never cause a false hit. A true result means the shapes are close enough to be worth an exact test, not that they actually intersect.

testCells(aCells: number[], bCells: number[]): boolean

Parameters

• aCells — number[].
• bCells — number[].

Returns

boolean

Example

import { Grid } from '@1pizzateam/spock';

const result = new Grid(100, 100, 10).testCells([1, 2, 3], [1, 2, 3]);

Grid.getFirstCommonCell()

Return the lowest common cell shared by both sorted lists, or -1 if disjoint.

getFirstCommonCell(aCells: number[], bCells: number[]): number

Parameters

• aCells — number[].
• bCells — number[].

Returns

number

Example

import { Grid } from '@1pizzateam/spock';

const firstCell = new Grid(100, 100, 10).getFirstCommonCell([1, 4, 7], [4, 7, 9]); // 4

Grid.isFirstCommonCell()

Fast deduplication check: returns true only if cellId is the first common cell between aCells and bCells.

isFirstCommonCell(aCells: number[], bCells: number[], cellId: number): boolean

Parameters

• aCells — number[].
• bCells — number[].
• cellId — number.

Returns

boolean

Grid.getCell()

Get cell index at (x, y) coordinates, or -1 if out of bounds.

getCell(x: number, y: number): number

Parameters

• x — number.
• y — number.

Returns

number

Example

import { Grid } from '@1pizzateam/spock';

const cellIndex = new Grid(100, 100, 10).getCell(25, 15); // cell at (2, 1) -> 12

Grid.getCellCoords()

Decompose a cell index into column and row vector coordinates.

getCellCoords(cellId: number, target?: Vec2): Vec2

Parameters

• cellId — number.
• target — Vec2. Optional.

Returns

Vec2

Grid.draw()

Draw the lattice on a canvas.

Paints the lattice, optionally filling the background first. Pass an empty string for either colour to skip that pass.

draw(context: CanvasRenderingContext2D, fillColor: string, strokeColor: string, strokeWidth: number): void

Parameters

• context — CanvasRenderingContext2D.
• fillColor — string.
• strokeColor — string.
• strokeWidth — number.

Returns

void

Example

import { Grid } from '@1pizzateam/spock';

const context = document.querySelector('canvas').getContext('2d');

const result = new Grid(100, 100, 10).draw(context, '#5b8cff', '#5b8cff', 1);