From bc7fa4fc1cf0c54854d6ef15940e16f9bafe83c6 Mon Sep 17 00:00:00 2001
From: Jamie Wong <jamie.lf.wong@gmail.com>
Date: Sun, 26 Nov 2017 20:03:34 -0800
Subject: [PATCH] simple pinch-to-zoom support

---
 flamechart.tsx | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/flamechart.tsx b/flamechart.tsx
index cefe29e..b9db721 100644
--- a/flamechart.tsx
+++ b/flamechart.tsx
@@ -391,9 +391,17 @@ export class FlamechartView extends Component<FlamechartViewProps, void> {
     // initiated momentum scrolling may still take effect.
     // Figure out how to prevent this.
     //
-    // Also, support drag-based panning, and pinch-to-zoom
-    if (ev.metaKey) {
-      const multiplier = 1 + (ev.deltaY / 100)
+    // Also, support drag-based panning.
+    if (ev.metaKey || ev.ctrlKey) {
+      let multiplier = 1 + (ev.deltaY / 100)
+
+      // On Chrome & Firefox, pinch-to-zoom maps to
+      // WheelEvent + Ctrl Key. We'll accelerate it in
+      // this case, since it feels a bit sluggish otherwise.
+      if (ev.ctrlKey) {
+        multiplier = 1 + (ev.deltaY / 40)
+      }
+
       this.zoom(new Vec2(ev.offsetX, ev.offsetY), multiplier)
     } else {
       this.pan(new Vec2(ev.deltaX, ev.deltaY))