1 files changed, 42 insertions, 0 deletions
diff --git a/src_js/dragger.ts b/src_js/dragger.ts
new file mode 100644
index 0000000..0aeda91
--- /dev/null
+++ b/src_js/dragger.ts
@@ -0,0 +1,42 @@
+
+type MouseHandler = (evt: MouseEvent) => void;
+
+type MoveHandler = (evt: MouseEvent, dx: number, dy: number) => void;
+
+type CreateMoveHandler = (evt: MouseEvent) => MoveHandler;
+
+type Dragger = {
+    initX: number,
+    initY: number,
+    moveHandler: MoveHandler;
+}
+
+
+const draggers: Dragger[] = [];
+
+
+export function mouseDownHandler(
+    createMoveHandlerCb: CreateMoveHandler
+): MouseHandler {
+    return evt => {
+        draggers.push({
+            initX: evt.screenX,
+            initY: evt.screenY,
+            moveHandler: createMoveHandlerCb(evt)
+        });
+    };
+}
+
+
+document.addEventListener('mousemove', evt => {
+    for (const dragger of draggers) {
+        const dx = evt.screenX - dragger.initX;
+        const dy = evt.screenY - dragger.initY;
+        dragger.moveHandler(evt, dx, dy);
+    }
+});
+
+
+document.addEventListener('mouseup', () => {
+    draggers.splice(0);
+});