Modified scene.show to calculate the mouse position inside the scene, and created an example scene_circle_painter to demonstrate a usecase #7149
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…, and demonstrated the usage in a created example scene_circle_placer
…/scene from change
emilk
reviewed
Jun 15, 2025
| &mut self.scene_rect, | ||
| &mut mouse_position_in_scene, | ||
| |ui| { | ||
| 8000 for circle_pos in &self.circles_in_scene { |
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Instead of changing the Scene API, you can get the mouse coordinate with:
mouse_position_in_scene =
ctx.layer_transform_from_global(ui.painter().layer_id()).unwrap_or_default() *
ui.input(|i| i.pointer.latest_pos());If you add a couple of helpers to Painter this could be shortend to
mouse_position_in_scene =
ui.painter().layer_transform_from_global() * ui.input(|i| i.pointer.latest_pos());
emilk
requested changes
Jun 15, 2025
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Features/changes added
I have modified egui/crates/egui/src/containers/scene.rs, to now also calculate the mouse position inside the scene, dependent on both translation and scale. This has been accomplished by having scene.show also have a mutable borrow of a mouse_position as input, and using the to_global variable inside the show function to calculate the scene mouse position.
Along with this, I have created an example called scene_circle_placer to demonstrate a use case, and have fixed errors that appeared in crates/egui_demo_lib/src/demo/scene.rs due to the change.
Reason
Currently, there is no intuitive way of getting the position of the mouse inside of the scene. It has been possible for me to find the position using the scene response, but the position is not correct when hovering over other interactive elements, such as buttons, making it difficult to create for example dragging behavior of drawn elements.
Issues fixed with this PR
#7060
Note
Due to the nature of the mouse position, I have not been able to find a way to avoid using unwrap, however, I have been very careful not to create any unaccounted situations.
Cargo fmt and cargo clippy has been run successfully.
The command UPDATE_SNAPSHOTS=true cargo test --workspace --all-features was run successfully, and this was the output from ./scripts/check.sh