feat: Add point param to increase/decreaseZoom

Co-authored-by: aider (vertex_ai/gemini-2.5-pro) <aider@aider.chat>

Author: jkgenser

src/Reader.tsx

@@ -212,16 +212,22 @@ const Reader = ({
     [virtualizer, viewports],
   );
 
-  const increaseZoom = (levels?: number) => {
-    const anchor = getVirtualItemAndOffsetAt();
+  const increaseZoom = (
+    levels?: number,
+    point?: { top?: number; left?: number },
+  ) => {
+    const anchor = getVirtualItemAndOffsetAt(point);
     if (anchor) {
       setScrollAnchor(anchor);
     }
     baseIncreaseZoom(levels);
   };
 
-  const decreaseZoom = (levels?: number) => {
-    const anchor = getVirtualItemAndOffsetAt();
+  const decreaseZoom = (
+    levels?: number,
+    point?: { top?: number; left?: number },
+  ) => {
+    const anchor = getVirtualItemAndOffsetAt(point);
     if (anchor) {
       setScrollAnchor(anchor);
     }

src/types.ts

@@ -48,8 +48,14 @@ export interface ReaderAPI {
   ) => void;
   jumpToHighlightArea: (area: HighlightArea) => void;
   jumpToOffset: (offset: number) => void;
-  increaseZoom: (levels?: number) => void;
-  decreaseZoom: (levels?: number) => void;
+  increaseZoom: (
+    levels?: number,
+    point?: { top?: number; left?: number },
+  ) => void;
+  decreaseZoom: (
+    levels?: number,
+    point?: { top?: number; left?: number },
+  ) => void;
   zoomFitWidth: () => void;
   rotateClockwise: () => void;
   rotateCounterClockwise: () => void;