Initial commit 🎉

fbshipit-source-id: b6fc29740c6875d2e78953b8a7123890a67930f2
Co-authored-by: Sebastian McKenzie <sebmck@fb.com>
Co-authored-by: John Knox <jknox@fb.com>
Co-authored-by: Emil Sjölander <emilsj@fb.com>
Co-authored-by: Pritesh Nandgaonkar <prit91@fb.com>

src/utils/snap.js

@@ -0,0 +1,159 @@
+/**
+ * Copyright 2018-present Facebook.
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ * @format
+ */
+
+import type {Rect} from './geometry.js';
+
+export const SNAP_SIZE = 16;
+
+export function snapGrid(val: number): number {
+  return val - val % SNAP_SIZE;
+}
+
+export function getPossibleSnappedPosition(
+  windows: Array<Rect>,
+  {
+    getGap,
+    getNew,
+  }: {
+    getNew: (win: Rect) => number,
+    getGap: (win: Rect) => number,
+  },
+): ?number {
+  for (const win of windows) {
+    const gap = Math.abs(getGap(win));
+    if (gap >= 0 && gap < SNAP_SIZE) {
+      return getNew(win);
+    }
+  }
+}
+
+export function getDistanceTo(props: Rect, win: Rect): number {
+  const x1 = win.left;
+  const y1 = win.top;
+  const x1b = win.left + win.width;
+  const y1b = win.top + win.height;
+
+  const x2 = props.left;
+  const y2 = props.top;
+  const x2b = props.left + props.width;
+  const y2b = props.top + props.height;
+
+  const left = x2b < x1;
+  const right = x1b < x2;
+  const bottom = y2b < y1;
+  const top = y1b < y2;
+
+  if (top && left) {
+    return distance(x1, y1b, x2b, y2);
+  } else if (left && bottom) {
+    return distance(x1, y1, x2b, y2b);
+  } else if (bottom && right) {
+    return distance(x1b, y1, x2, y2b);
+  } else if (right && top) {
+    return distance(x1b, y1b, x2, y2);
+  } else if (left) {
+    return x1 - x2b;
+  } else if (right) {
+    return x2 - x1b;
+  } else if (bottom) {
+    return y1 - y2b;
+  } else if (top) {
+    return y2 - y1b;
+  } else {
+    return 0;
+  }
+}
+
+export function distance(
+  x1: number,
+  y1: number,
+  x2: number,
+  y2: number,
+): number {
+  return Math.abs(x1 - x2) + Math.abs(y1 - y2);
+}
+
+export function maybeSnapLeft(
+  props: Rect,
+  windows: Array<Rect>,
+  left: number,
+): number {
+  // snap right side to left
+  // ┌─┬─┐
+  // │A│B│
+  // └─┴─┘
+  const snapRight = getPossibleSnappedPosition(windows, {
+    debug: true,
+    getGap: win => win.left - (props.width + left),
+    getNew: win => win.left - props.width,
+  });
+  if (snapRight != null) {
+    return snapRight;
+  }
+
+  // snap left side to right
+  // ┌─┬─┐
+  // │B│A│
+  // └─┴─┘
+  const snapLeft = getPossibleSnappedPosition(windows, {
+    getGap: win => left - (win.left + win.width),
+    getNew: win => win.left + win.width,
+  });
+  if (snapLeft != null) {
+    return snapLeft;
+  }
+
+  return snapGrid(left);
+}
+
+export function maybeSnapTop(
+  props: Rect,
+  windows: Array<Rect>,
+  top: number,
+): number {
+  // snap bottom to bottom
+  // ┌─┐
+  // │A├─┐
+  // │ │B│
+  // └─┴─┘
+  const snapBottom2 = getPossibleSnappedPosition(windows, {
+    getGap: win => top - win.top - win.height,
+    getNew: win => win.top + win.height,
+  });
+  if (snapBottom2 != null) {
+    return snapBottom2;
+  }
+
+  // snap top to bottom
+  // ┌─┐
+  // │B│
+  // ├─┤
+  // │A│
+  // └─┘
+  const snapBottom = getPossibleSnappedPosition(windows, {
+    getGap: win => top - win.top - win.height,
+    getNew: win => win.top + win.height,
+  });
+  if (snapBottom != null) {
+    return snapBottom;
+  }
+
+  // snap top to top
+  // ┌─┬─┐
+  // │A│B│
+  // │ ├─┘
+  // └─┘
+  const snapTop = getPossibleSnappedPosition(windows, {
+    getGap: win => top - win.top,
+    getNew: win => win.top,
+  });
+  if (snapTop != null) {
+    return snapTop;
+  }
+
+  return snapGrid(top);
+}