From cd3e9ea5b68107c34449f6355c7076ca5621bae4 Mon Sep 17 00:00:00 2001
From: Colin Cai <104604363+Creative0708@users.noreply.github.com>
Date: Thu, 20 Jun 2024 04:43:51 -0400
Subject: [PATCH] Fix: `Response::hover_pos` returns incorrect positions with
 layer transforms (#4679)

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When layer transforms are present, the `Response::hover_pos` function in
egui returns `transform * pos` instead of `transform.inverse() * pos`.
This is incorrect and isn't consistent with [how egui calculates other
interaction
positions](https://github.com/emilk/egui/blob/master/crates/egui/src/context.rs#L1193).

See:
https://github.com/emilk/egui/blob/master/crates/egui/src/response.rs#L471

This PR fixes this bug, changing `transform` to `transform.inverse()`.
Nothing fancy here, just a one-line change. `scripts/check.sh` runs
successfully.


Below are videos of before and after with a modified version of the web
demo. I added another entry after
https://github.com/emilk/egui/blob/master/crates/egui_demo_lib/src/demo/pan_zoom.rs#L108
with a debug rectangle drawn at the return value of `hover_pos`:
```rust
(
    egui::Pos2::new(120.0, 120.0),
    Box::new(|ui, _state| {
        let response =
            ui.allocate_response(egui::Vec2::splat(128.0), egui::Sense::hover());
        ui.painter().rect_filled(
            egui::Rect::from_center_size(
                response.hover_pos().unwrap_or_default(),
                egui::Vec2::splat(8.0),
            ),
            egui::Rounding::ZERO,
            egui::Color32::DEBUG_COLOR,
        );
        response
    }),
),
```

Without the fix:

https://github.com/emilk/egui/assets/104604363/241cfcab-88ab-459b-8f4d-3367da3aa392

With the fix:

https://github.com/emilk/egui/assets/104604363/e52a7263-44c7-42c1-be46-1ecadc025625
---
 crates/egui/src/response.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crates/egui/src/response.rs b/crates/egui/src/response.rs
index 64b2ff198..192c573ff 100644
--- a/crates/egui/src/response.rs
+++ b/crates/egui/src/response.rs
@@ -468,7 +468,7 @@ impl Response {
                 .ctx
                 .memory(|m| m.layer_transforms.get(&self.layer_id).copied())
             {
-                pos = transform * pos;
+                pos = transform.inverse() * pos;
             }
             Some(pos)
         } else {