feat: Add option to flip single element on the context menu (#2520)

Co-authored-by: dwelle <luzar.david@gmail.com>

src/actions/actionFlip.ts

@@ -0,0 +1,207 @@
+import { register } from "./register";
+import { getSelectedElements } from "../scene";
+import { getElementMap, getNonDeletedElements } from "../element";
+import { mutateElement } from "../element/mutateElement";
+import { ExcalidrawElement, NonDeleted } from "../element/types";
+import { normalizeAngle, resizeSingleElement } from "../element/resizeElements";
+import { AppState } from "../types";
+import { getTransformHandles } from "../element/transformHandles";
+import { isLinearElement } from "../element/typeChecks";
+import { updateBoundElements } from "../element/binding";
+import { LinearElementEditor } from "../element/linearElementEditor";
+
+const enableActionFlipHorizontal = (
+  elements: readonly ExcalidrawElement[],
+  appState: AppState,
+) => {
+  const eligibleElements = getSelectedElements(
+    getNonDeletedElements(elements),
+    appState,
+  );
+  return eligibleElements.length === 1 && eligibleElements[0].type !== "text";
+};
+
+const enableActionFlipVertical = (
+  elements: readonly ExcalidrawElement[],
+  appState: AppState,
+) => {
+  const eligibleElements = getSelectedElements(
+    getNonDeletedElements(elements),
+    appState,
+  );
+  return eligibleElements.length === 1;
+};
+
+export const actionFlipHorizontal = register({
+  name: "flipHorizontal",
+  perform: (elements, appState) => {
+    return {
+      elements: flipSelectedElements(elements, appState, "horizontal"),
+      appState,
+      commitToHistory: true,
+    };
+  },
+  keyTest: (event) => event.shiftKey && event.code === "KeyH",
+  contextItemLabel: "labels.flipHorizontal",
+  contextItemPredicate: (elements, appState) =>
+    enableActionFlipHorizontal(elements, appState),
+});
+
+export const actionFlipVertical = register({
+  name: "flipVertical",
+  perform: (elements, appState) => {
+    return {
+      elements: flipSelectedElements(elements, appState, "vertical"),
+      appState,
+      commitToHistory: true,
+    };
+  },
+  keyTest: (event) => event.shiftKey && event.code === "KeyV",
+  contextItemLabel: "labels.flipVertical",
+  contextItemPredicate: (elements, appState) =>
+    enableActionFlipVertical(elements, appState),
+});
+
+const flipSelectedElements = (
+  elements: readonly ExcalidrawElement[],
+  appState: Readonly<AppState>,
+  flipDirection: "horizontal" | "vertical",
+) => {
+  const selectedElements = getSelectedElements(
+    getNonDeletedElements(elements),
+    appState,
+  );
+
+  // remove once we allow for groups of elements to be flipped
+  if (selectedElements.length > 1) {
+    return elements;
+  }
+
+  const updatedElements = flipElements(
+    selectedElements,
+    appState,
+    flipDirection,
+  );
+
+  const updatedElementsMap = getElementMap(updatedElements);
+
+  return elements.map((element) => updatedElementsMap[element.id] || element);
+};
+
+const flipElements = (
+  elements: NonDeleted<ExcalidrawElement>[],
+  appState: AppState,
+  flipDirection: "horizontal" | "vertical",
+): ExcalidrawElement[] => {
+  for (let i = 0; i < elements.length; i++) {
+    flipElement(elements[i], appState);
+    // If vertical flip, rotate an extra 180
+    if (flipDirection === "vertical") {
+      rotateElement(elements[i], Math.PI);
+    }
+  }
+  return elements;
+};
+
+const flipElement = (
+  element: NonDeleted<ExcalidrawElement>,
+  appState: AppState,
+) => {
+  const originalX = element.x;
+  const originalY = element.y;
+  const width = element.width;
+  const height = element.height;
+  const originalAngle = normalizeAngle(element.angle);
+
+  let finalOffsetX = 0;
+  if (isLinearElement(element)) {
+    finalOffsetX =
+      element.points.reduce((max, point) => Math.max(max, point[0]), 0) * 2 -
+      element.width;
+  }
+
+  // Rotate back to zero, if necessary
+  mutateElement(element, {
+    angle: normalizeAngle(0),
+  });
+  // Flip unrotated by pulling TransformHandle to opposite side
+  const transformHandles = getTransformHandles(element, appState.zoom);
+  let usingNWHandle = true;
+  let newNCoordsX = 0;
+  let nHandle = transformHandles.nw;
+  if (!nHandle) {
+    // Use ne handle instead
+    usingNWHandle = false;
+    nHandle = transformHandles.ne;
+    if (!nHandle) {
+      mutateElement(element, {
+        angle: originalAngle,
+      });
+      return;
+    }
+  }
+
+  if (isLinearElement(element)) {
+    for (let i = 1; i < element.points.length; i++) {
+      LinearElementEditor.movePoint(element, i, [
+        -element.points[i][0],
+        element.points[i][1],
+      ]);
+    }
+    LinearElementEditor.normalizePoints(element);
+  } else {
+    // calculate new x-coord for transformation
+    newNCoordsX = usingNWHandle ? element.x + 2 * width : element.x - 2 * width;
+    resizeSingleElement(
+      element,
+      true,
+      element,
+      usingNWHandle ? "nw" : "ne",
+      false,
+      newNCoordsX,
+      nHandle[1],
+    );
+    // fix the size to account for handle sizes
+    mutateElement(element, {
+      width,
+      height,
+    });
+  }
+
+  // Rotate by (360 degrees - original angle)
+  let angle = normalizeAngle(2 * Math.PI - originalAngle);
+  if (angle < 0) {
+    // check, probably unnecessary
+    angle = normalizeAngle(angle + 2 * Math.PI);
+  }
+  mutateElement(element, {
+    angle,
+  });
+
+  // Move back to original spot to appear "flipped in place"
+  mutateElement(element, {
+    x: originalX + finalOffsetX,
+    y: originalY,
+  });
+
+  updateBoundElements(element);
+};
+
+const rotateElement = (element: ExcalidrawElement, rotationAngle: number) => {
+  const originalX = element.x;
+  const originalY = element.y;
+  let angle = normalizeAngle(element.angle + rotationAngle);
+  if (angle < 0) {
+    // check, probably unnecessary
+    angle = normalizeAngle(2 * Math.PI + angle);
+  }
+  mutateElement(element, {
+    angle,
+  });
+
+  // Move back to original spot
+  mutateElement(element, {
+    x: originalX,
+    y: originalY,
+  });
+};

src/actions/index.ts

@@ -66,6 +66,8 @@ export {
   distributeVertically,
 } from "./actionDistribute";
 
+export { actionFlipHorizontal, actionFlipVertical } from "./actionFlip";
+
 export {
   actionCopy,
   actionCut,

src/actions/shortcuts.ts

@@ -23,7 +23,9 @@ export type ShortcutName =
   | "zenMode"
   | "stats"
   | "addToLibrary"
-  | "viewMode";
+  | "viewMode"
+  | "flipHorizontal"
+  | "flipVertical";
 
 const shortcutMap: Record<ShortcutName, string[]> = {
   cut: [getShortcutKey("CtrlOrCmd+X")],
@@ -57,6 +59,8 @@ const shortcutMap: Record<ShortcutName, string[]> = {
   zenMode: [getShortcutKey("Alt+Z")],
   stats: [],
   addToLibrary: [],
+  flipHorizontal: [getShortcutKey("Shift+H")],
+  flipVertical: [getShortcutKey("Shift+V")],
   viewMode: [getShortcutKey("Alt+R")],
 };
 

src/actions/types.ts

@@ -85,6 +85,8 @@ export type ActionName =
   | "alignHorizontallyCentered"
   | "distributeHorizontally"
   | "distributeVertically"
+  | "flipHorizontal"
+  | "flipVertical"
   | "viewMode"
   | "exportWithDarkMode";