Add brush and grid snapping functionality

src/geometry/box-brush.ts

@@ -0,0 +1,47 @@
+import type { Vec3 } from "../core/vector";
+import type { BoxBrush } from "../document/brushes";
+
+export interface BoxBrushBounds {
+  min: Vec3;
+  max: Vec3;
+}
+
+export function getBoxBrushHalfSize(brush: BoxBrush): Vec3 {
+  return {
+    x: brush.size.x * 0.5,
+    y: brush.size.y * 0.5,
+    z: brush.size.z * 0.5
+  };
+}
+
+export function getBoxBrushBounds(brush: BoxBrush): BoxBrushBounds {
+  const halfSize = getBoxBrushHalfSize(brush);
+
+  return {
+    min: {
+      x: brush.center.x - halfSize.x,
+      y: brush.center.y - halfSize.y,
+      z: brush.center.z - halfSize.z
+    },
+    max: {
+      x: brush.center.x + halfSize.x,
+      y: brush.center.y + halfSize.y,
+      z: brush.center.z + halfSize.z
+    }
+  };
+}
+
+export function getBoxBrushCornerPositions(brush: BoxBrush): Vec3[] {
+  const bounds = getBoxBrushBounds(brush);
+
+  return [
+    { x: bounds.min.x, y: bounds.min.y, z: bounds.min.z },
+    { x: bounds.max.x, y: bounds.min.y, z: bounds.min.z },
+    { x: bounds.min.x, y: bounds.max.y, z: bounds.min.z },
+    { x: bounds.max.x, y: bounds.max.y, z: bounds.min.z },
+    { x: bounds.min.x, y: bounds.min.y, z: bounds.max.z },
+    { x: bounds.max.x, y: bounds.min.y, z: bounds.max.z },
+    { x: bounds.min.x, y: bounds.max.y, z: bounds.max.z },
+    { x: bounds.max.x, y: bounds.max.y, z: bounds.max.z }
+  ];
+}

src/geometry/grid-snapping.ts

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+import type { Vec3 } from "../core/vector";
+
+export const DEFAULT_GRID_SIZE = 1;
+
+function assertGridSize(gridSize: number): number {
+  if (!Number.isFinite(gridSize) || gridSize <= 0) {
+    throw new Error("Grid size must be a positive finite number.");
+  }
+
+  return gridSize;
+}
+
+export function snapValueToGrid(value: number, gridSize = DEFAULT_GRID_SIZE): number {
+  const step = assertGridSize(gridSize);
+
+  if (!Number.isFinite(value)) {
+    throw new Error("Grid-snapped values must be finite numbers.");
+  }
+
+  return Math.round(value / step) * step;
+}
+
+function snapPositiveSizeValue(value: number, gridSize: number): number {
+  if (!Number.isFinite(value)) {
+    throw new Error("Box brush size values must be finite numbers.");
+  }
+
+  const snappedSize = Math.round(Math.abs(value) / gridSize) * gridSize;
+  return snappedSize > 0 ? snappedSize : gridSize;
+}
+
+export function snapVec3ToGrid(vector: Vec3, gridSize = DEFAULT_GRID_SIZE): Vec3 {
+  return {
+    x: snapValueToGrid(vector.x, gridSize),
+    y: snapValueToGrid(vector.y, gridSize),
+    z: snapValueToGrid(vector.z, gridSize)
+  };
+}
+
+export function snapPositiveSizeToGrid(size: Vec3, gridSize = DEFAULT_GRID_SIZE): Vec3 {
+  const step = assertGridSize(gridSize);
+
+  return {
+    x: snapPositiveSizeValue(size.x, step),
+    y: snapPositiveSizeValue(size.y, step),
+    z: snapPositiveSizeValue(size.z, step)
+  };
+}