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Document grid operations

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This commit is contained in:
Robin Townsend 2023-02-13 12:17:09 -05:00
parent d852e33413
commit 5448744871
1 changed files with 81 additions and 33 deletions
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114
src/video-grid/model.ts
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@ -48,21 +48,33 @@ export interface Grid {
cells: (Cell | undefined)[];
}
export function dijkstra(g: Grid): number[] {
const end = findLast1By1Index(g) ?? 0;
const endRow = row(end, g);
const endColumn = column(end, g);
/**
* Gets the paths that tiles should travel along in the grid to reach a
* particular destination.
* @param dest The destination index.
* @param g The grid.
* @returns An array in which each cell holds the index of the next cell to move
* to to reach the destination, or null if it is the destination.
*/
export function getPaths(dest: number, g: Grid): (number | null)[] {
const destRow = row(dest, g);
const destColumn = column(dest, g);
const distances = new Array<number>(end + 1).fill(Infinity);
distances[end] = 0;
const edges = new Array<number | undefined>(end).fill(undefined);
const heap = new TinyQueue([end], (i) => distances[i]);
// This is Dijkstra's algorithm
const distances = new Array<number>(dest + 1).fill(Infinity);
distances[dest] = 0;
const edges = new Array<number | null | undefined>(dest).fill(undefined);
edges[dest] = null;
const heap = new TinyQueue([dest], (i) => distances[i]);
const visit = (curr: number, via: number) => {
const viaCell = g.cells[via];
const viaLargeTile =
viaCell !== undefined && (viaCell.rows > 1 || viaCell.columns > 1);
const distanceVia = distances[via] + (viaLargeTile ? 4 : 1);
// Since it looks nicer to have paths go around large tiles, we impose an
// increased cost for moving through them
const distanceVia = distances[via] + (viaLargeTile ? 8 : 1);
if (distanceVia < distances[curr]) {
distances[curr] = distanceVia;
@ -76,18 +88,20 @@ export function dijkstra(g: Grid): number[] {
const viaRow = row(via, g);
const viaColumn = column(via, g);
// Visit each neighbor
if (viaRow > 0) visit(via - g.columns, via);
if (viaColumn > 0) visit(via - 1, via);
if (viaColumn < (viaRow === endRow ? endColumn : g.columns - 1))
if (viaColumn < (viaRow === destRow ? destColumn : g.columns - 1))
visit(via + 1, via);
if (
viaRow < endRow - 1 ||
(viaRow === endRow - 1 && viaColumn <= endColumn)
viaRow < destRow - 1 ||
(viaRow === destRow - 1 && viaColumn <= destColumn)
)
visit(via + g.columns, via);
}
return edges as number[];
// The heap is empty, so we've generated all paths
return edges as (number | null)[];
}
function findLastIndex<T>(
@ -194,27 +208,30 @@ function getNextGap(g: Grid): number | null {
return null;
}
/**
* Backfill any gaps in the grid.
*/
export function fillGaps(g: Grid): Grid {
const result: Grid = { ...g, cells: [...g.cells] };
let gap = getNextGap(result);
if (gap !== null) {
const pathToEnd = dijkstra(result);
const pathsToEnd = getPaths(findLast1By1Index(result)!, result);
do {
let filled = false;
let to = gap;
let from: number | undefined = pathToEnd[gap];
let from = pathsToEnd[gap];
// First, attempt to fill the gap by moving 1×1 tiles backwards from the
// end of the grid along a set path
while (from !== undefined) {
while (from !== null) {
const toCell = result.cells[to];
const fromCell = result.cells[from];
// Skip over large tiles
// Skip over slots that are already full
if (toCell !== undefined) {
to = pathToEnd[to];
to = pathsToEnd[to]!;
// Skip over large tiles. Also, we might run into gaps along the path
// created during the filling of previous gaps. Skip over those too;
// they'll be picked up on the next iteration of the outer loop.
@ -223,13 +240,13 @@ export function fillGaps(g: Grid): Grid {
fromCell.rows > 1 ||
fromCell.columns > 1
) {
from = pathToEnd[from];
from = pathsToEnd[from];
} else {
result.cells[to] = result.cells[from];
result.cells[from] = undefined;
filled = true;
to = pathToEnd[to];
from = pathToEnd[from];
to = pathsToEnd[to]!;
from = pathsToEnd[from];
}
}
@ -272,6 +289,12 @@ export function appendItems(items: TileDescriptor[], g: Grid): Grid {
};
}
/**
* Changes the size of a tile, rearranging the grid to make space.
* @param tileId The ID of the tile to modify.
* @param g The grid.
* @returns The updated grid.
*/
export function cycleTileSize(tileId: string, g: Grid): Grid {
const from = g.cells.findIndex((c) => c?.item.id === tileId);
if (from === -1) return g; // Tile removed, no change
@ -279,63 +302,84 @@ export function cycleTileSize(tileId: string, g: Grid): Grid {
const fromHeight = g.cells[from]!.rows;
const fromEnd = areaEnd(from, fromWidth, fromHeight, g);
// The target dimensions, which toggle between 1×1 and larger than 1×1
const [toWidth, toHeight] =
fromWidth === 1 && fromHeight === 1
? [Math.min(3, Math.max(2, g.columns - 1)), 2]
: [1, 1];
// If we're expanding the tile, we want to create enough new rows at the
// tile's target position such that every new unit of grid area created during
// the expansion can fit within the new rows.
// We do it this way, since it's easier to backfill gaps in the grid than it
// is to push colliding tiles outwards.
const newRows = Math.max(
0,
Math.ceil((toWidth * toHeight - fromWidth * fromHeight) / g.columns)
);
const candidateWidth = toWidth;
const candidateHeight = toHeight - newRows;
// This is the grid with the new rows added
const gappyGrid: Grid = {
...g,
cells: new Array(g.cells.length + newRows * g.columns),
};
const nextScanLocations = new Set<number>([from]);
// The next task is to scan for a spot to place the modified tile. Since we
// might be creating new rows at the target position, this spot can be shorter
// than the target height.
const candidateWidth = toWidth;
const candidateHeight = toHeight - newRows;
// To make the tile appear to expand outwards from its center, we're actually
// scanning for locations to put the *center* of the tile. These numbers are
// the offsets between the tile's origin and its center.
const scanColumnOffset = Math.floor((toWidth - 1) / 2);
const scanRowOffset = Math.floor((toHeight - 1) / 2);
const nextScanLocations = new Set<number>([from]);
const rows = row(g.cells.length - 1, g) + 1;
let to: number | null = null;
// The contents of a given cell are 'displaceable' if it's empty, holds a 1×1
// tile, or is part of the original tile we're trying to reposition
const displaceable = (c: Cell | undefined, i: number): boolean =>
c === undefined ||
(c.columns === 1 && c.rows === 1) ||
inArea(i, from, fromEnd, g);
// Do the scanning
for (const scanLocation of nextScanLocations) {
const start = scanLocation - scanColumnOffset - g.columns * scanRowOffset;
const end = areaEnd(start, candidateWidth, candidateHeight, g);
const startColumn = column(start, g);
const startRow = row(start, g);
const endColumn = column(end, g);
const endRow = row(end, g);
if (
start >= 0 &&
end < gappyGrid.cells.length &&
endColumn - startColumn + 1 === candidateWidth
endColumn - startColumn + 1 === candidateWidth &&
allCellsInArea(start, end, g, displaceable)
) {
if (allCellsInArea(start, end, g, displaceable)) {
to = start;
break;
}
// This location works!
to = start;
break;
}
// Scan outwards in all directions
if (startColumn > 0) nextScanLocations.add(scanLocation - 1);
if (endColumn < g.columns - 1) nextScanLocations.add(scanLocation + 1);
if (startRow > 0) nextScanLocations.add(scanLocation - g.columns);
if (startRow <= rows) nextScanLocations.add(scanLocation + g.columns);
if (endRow < rows - 1) nextScanLocations.add(scanLocation + g.columns);
}
// TODO: Don't give up on placing the tile yet
// If there is no space in the grid, give up
if (to === null) return g;
const toRow = row(to, g);
// Copy tiles from the original grid to the new one, with the new rows
// inserted at the target location
g.cells.forEach((c, src) => {
if (c?.origin && c.item.id !== tileId) {
const offset =
@ -346,6 +390,8 @@ export function cycleTileSize(tileId: string, g: Grid): Grid {
}
});
// Place the tile in its target position, making a note of the tiles being
// overwritten
const displacedTiles: Cell[] = [];
const toEnd = areaEnd(to, toWidth, toHeight, g);
forEachCellInArea(to, toEnd, gappyGrid, (c, i) => {
@ -358,10 +404,12 @@ export function cycleTileSize(tileId: string, g: Grid): Grid {
};
});
// Place the displaced tiles in the remaining space
for (let i = 0; displacedTiles.length > 0; i++) {
if (gappyGrid.cells[i] === undefined)
gappyGrid.cells[i] = displacedTiles.shift();
}
// Fill any gaps that remain
return fillGaps(gappyGrid);
}