package.index.mjs Maven / Gradle / Ivy
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A tiny library for packing 2D rectangles (for sprite layouts)
export default function potpack(boxes) {
// calculate total box area and maximum box width
let area = 0;
let maxWidth = 0;
for (const box of boxes) {
area += box.w * box.h;
maxWidth = Math.max(maxWidth, box.w);
}
// sort the boxes for insertion by height, descending
boxes.sort((a, b) => b.h - a.h);
// aim for a squarish resulting container,
// slightly adjusted for sub-100% space utilization
const startWidth = Math.max(Math.ceil(Math.sqrt(area / 0.95)), maxWidth);
// start with a single empty space, unbounded at the bottom
const spaces = [{x: 0, y: 0, w: startWidth, h: Infinity}];
let width = 0;
let height = 0;
for (const box of boxes) {
// look through spaces backwards so that we check smaller spaces first
for (let i = spaces.length - 1; i >= 0; i--) {
const space = spaces[i];
// look for empty spaces that can accommodate the current box
if (box.w > space.w || box.h > space.h) continue;
// found the space; add the box to its top-left corner
// |-------|-------|
// | box | |
// |_______| |
// | space |
// |_______________|
box.x = space.x;
box.y = space.y;
height = Math.max(height, box.y + box.h);
width = Math.max(width, box.x + box.w);
if (box.w === space.w && box.h === space.h) {
// space matches the box exactly; remove it
const last = spaces.pop();
if (i < spaces.length) spaces[i] = last;
} else if (box.h === space.h) {
// space matches the box height; update it accordingly
// |-------|---------------|
// | box | updated space |
// |_______|_______________|
space.x += box.w;
space.w -= box.w;
} else if (box.w === space.w) {
// space matches the box width; update it accordingly
// |---------------|
// | box |
// |_______________|
// | updated space |
// |_______________|
space.y += box.h;
space.h -= box.h;
} else {
// otherwise the box splits the space into two spaces
// |-------|-----------|
// | box | new space |
// |_______|___________|
// | updated space |
// |___________________|
spaces.push({
x: space.x + box.w,
y: space.y,
w: space.w - box.w,
h: box.h
});
space.y += box.h;
space.h -= box.h;
}
break;
}
}
return {
w: width, // container width
h: height, // container height
fill: (area / (width * height)) || 0 // space utilization
};
}