From 79c3748b0eb2a73d4b27d90644c82a0f0180f3c6 Mon Sep 17 00:00:00 2001
From: syntaxbullet <syntaxbullet@protonmail.com>
Date: Fri, 3 Jul 2026 09:47:05 +0200
Subject: [PATCH] feat(input): add viewport wheel zoom and panning

---
 input/index.ts          |  3 +-
 input/viewport.ts       | 56 ++++++++++++++++++++++++++++-
 view/CanvasViewport.tsx | 78 ++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 134 insertions(+), 3 deletions(-)

diff --git a/input/index.ts b/input/index.ts
index f6043d9..0050258 100644
--- a/input/index.ts
+++ b/input/index.ts
@@ -6,4 +6,5 @@ export {
 export type { CommandKeybind, GlobalKeybindConsumer, Keybind, KeybindEvent, KeybindMap } from "./keyboard";
 export { handleKeybind, keybindFromEvent } from "./keyboard";
 export type { GlobalPointerConsumer, GlobalWheelConsumer, PointerInputEvent, WheelInputEvent } from "./pointer";
-export { handleViewportWheel } from "./viewport";
+export type { ViewportPointerPanHandler } from "./viewport";
+export { createViewportPointerPanHandler, handleViewportWheel } from "./viewport";
diff --git a/input/viewport.ts b/input/viewport.ts
index 13b9b5d..955363b 100644
--- a/input/viewport.ts
+++ b/input/viewport.ts
@@ -1,5 +1,59 @@
 import type { Dispatch } from "@commands/dispatcher";
-import type { GlobalWheelConsumer, WheelInputEvent } from "./pointer";
+import type { GlobalPointerConsumer, GlobalWheelConsumer, PointerInputEvent, WheelInputEvent } from "./pointer";
+
+export type ViewportPointerPanHandler = {
+  pointerDown(event: PointerInputEvent): boolean;
+  pointerMove(event: PointerInputEvent): boolean;
+  pointerUp(event: PointerInputEvent): boolean;
+};
+
+export function createViewportPointerPanHandler(options: {
+  globalConsumer: GlobalPointerConsumer;
+  dispatch: Dispatch;
+  getCurrentZoom: () => number;
+}): ViewportPointerPanHandler {
+  let activePointerId: number | undefined;
+  let lastPosition: PointerInputEvent["position"] | undefined;
+
+  const canPan = (event: PointerInputEvent) => event.pointerType !== "mouse" || (event.buttons & 4) === 4;
+
+  return {
+    pointerDown(event) {
+      if (options.globalConsumer(event)) return true;
+      if (!canPan(event)) return false;
+
+      activePointerId = event.pointerId;
+      lastPosition = event.position;
+      return true;
+    },
+    pointerMove(event) {
+      if (activePointerId !== event.pointerId || !lastPosition) return false;
+
+      const zoom = options.getCurrentZoom();
+      const screenDelta = {
+        x: event.position.x - lastPosition.x,
+        y: event.position.y - lastPosition.y,
+      };
+
+      lastPosition = event.position;
+      options.dispatch("viewport.pan", {
+        delta: {
+          x: -screenDelta.x / zoom,
+          y: -screenDelta.y / zoom,
+        },
+      });
+
+      return true;
+    },
+    pointerUp(event) {
+      if (activePointerId !== event.pointerId) return false;
+
+      activePointerId = undefined;
+      lastPosition = undefined;
+      return true;
+    },
+  };
+}
 
 export function handleViewportWheel(options: {
   event: WheelInputEvent;
diff --git a/view/CanvasViewport.tsx b/view/CanvasViewport.tsx
index 23ffe9f..7219453 100644
--- a/view/CanvasViewport.tsx
+++ b/view/CanvasViewport.tsx
@@ -1,12 +1,28 @@
 import { useEffect, useRef } from "react";
 import type { AppStore } from "@editor/store";
+import type { GlobalPointerConsumer, GlobalWheelConsumer } from "@input/index";
+import {
+  createViewportPointerPanHandler,
+  handleViewportWheel,
+  pointerInputEventFromPointerEvent,
+  wheelInputEventFromWheelEvent,
+} from "@input/index";
 import { createRenderer } from "@renderer/index";
 
+const ignoreGlobalPointer: GlobalPointerConsumer = () => false;
+const ignoreGlobalWheel: GlobalWheelConsumer = () => false;
+
 export type CanvasViewportProps = {
   store: AppStore;
+  globalPointerConsumer?: GlobalPointerConsumer;
+  globalWheelConsumer?: GlobalWheelConsumer;
 };
 
-export function CanvasViewport({ store }: CanvasViewportProps) {
+export function CanvasViewport({
+  store,
+  globalPointerConsumer = ignoreGlobalPointer,
+  globalWheelConsumer = ignoreGlobalWheel,
+}: CanvasViewportProps) {
   const canvasRef = useRef<HTMLCanvasElement | null>(null);
 
   useEffect(() => {
@@ -42,5 +58,65 @@ export function CanvasViewport({ store }: CanvasViewportProps) {
     return () => resizeObserver.disconnect();
   }, [store]);
 
+  useEffect(() => {
+    const canvas = canvasRef.current;
+    if (!canvas) return;
+
+    const panHandler = createViewportPointerPanHandler({
+      globalConsumer: globalPointerConsumer,
+      dispatch: store.dispatch,
+      getCurrentZoom: () => store.getState().editor.viewport.zoom,
+    });
+
+    const handlePointerDown = (event: PointerEvent) => {
+      const consumed = panHandler.pointerDown(pointerInputEventFromPointerEvent(event));
+      if (!consumed) return;
+
+      canvas.setPointerCapture(event.pointerId);
+      event.preventDefault();
+    };
+
+    const handlePointerMove = (event: PointerEvent) => {
+      const consumed = panHandler.pointerMove(pointerInputEventFromPointerEvent(event));
+      if (consumed) event.preventDefault();
+    };
+
+    const handlePointerUp = (event: PointerEvent) => {
+      const consumed = panHandler.pointerUp(pointerInputEventFromPointerEvent(event));
+      if (consumed) event.preventDefault();
+    };
+
+    canvas.addEventListener("pointerdown", handlePointerDown);
+    canvas.addEventListener("pointermove", handlePointerMove);
+    canvas.addEventListener("pointerup", handlePointerUp);
+    canvas.addEventListener("pointercancel", handlePointerUp);
+
+    return () => {
+      canvas.removeEventListener("pointerdown", handlePointerDown);
+      canvas.removeEventListener("pointermove", handlePointerMove);
+      canvas.removeEventListener("pointerup", handlePointerUp);
+      canvas.removeEventListener("pointercancel", handlePointerUp);
+    };
+  }, [globalPointerConsumer, store]);
+
+  useEffect(() => {
+    const canvas = canvasRef.current;
+    if (!canvas) return;
+
+    const handleWheel = (event: WheelEvent) => {
+      const consumed = handleViewportWheel({
+        event: wheelInputEventFromWheelEvent(event),
+        globalConsumer: globalWheelConsumer,
+        dispatch: store.dispatch,
+        currentZoom: store.getState().editor.viewport.zoom,
+      });
+
+      if (consumed) event.preventDefault();
+    };
+
+    canvas.addEventListener("wheel", handleWheel, { passive: false });
+    return () => canvas.removeEventListener("wheel", handleWheel);
+  }, [globalWheelConsumer, store]);
+
   return <canvas ref={canvasRef} className="h-full w-full" />;
 }