From f101d39e8d98f8385f99dbcc71c2c2bfda863f5c Mon Sep 17 00:00:00 2001
From: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>
Date: Tue, 28 Jan 2025 14:55:17 +0100
Subject: [PATCH] Auto-size Scene on what is available

---
 crates/egui/src/containers/scene.rs    | 22 ++++++-------------
 crates/egui_demo_lib/src/demo/scene.rs | 29 +++++++++++++++-----------
 2 files changed, 23 insertions(+), 28 deletions(-)

diff --git a/crates/egui/src/containers/scene.rs b/crates/egui/src/containers/scene.rs
index 20b7c03e934..7085d9d91b4 100644
--- a/crates/egui/src/containers/scene.rs
+++ b/crates/egui/src/containers/scene.rs
@@ -7,11 +7,9 @@
 
 use core::f32;
 
-use emath::{GuiRounding, Pos2};
+use emath::{GuiRounding, NumExt as _, Pos2};
 
-use crate::{
-    emath::TSTransform, load, LayerId, Rangef, Rect, Response, Sense, Ui, UiBuilder, Vec2,
-};
+use crate::{emath::TSTransform, LayerId, Rangef, Rect, Response, Sense, Ui, UiBuilder, Vec2};
 
 /// Creates a transformation that fits a given scene rectangle into the available screen size.
 ///
@@ -24,7 +22,8 @@ pub fn fit_to_rect_in_scene(rect_in_ui: Rect, rect_in_scene: Rect) -> TSTransfor
     let scale_y = available_size_in_ui.y / rect_in_scene.height();
 
     // Use the smaller of the two scales to ensure the whole rectangle fits on the screen.
-    let scale = scale_x.min(scale_y).min(1.0);
+    const MAX_SCALE: f32 = 1.0;
+    let scale = f32::min(scale_x, scale_y).at_most(MAX_SCALE);
 
     // Compute the translation to center the bounding rect in the screen.
     let center_screen = rect_in_ui.center();
@@ -40,7 +39,6 @@ pub fn fit_to_rect_in_scene(rect_in_ui: Rect, rect_in_scene: Rect) -> TSTransfor
 pub struct Scene {
     zoom_range: Rangef,
     max_inner_size: Vec2,
-    fit_rect: Option<Rect>,
 }
 
 impl Default for Scene {
@@ -48,7 +46,6 @@ impl Default for Scene {
         Self {
             zoom_range: Rangef::new(f32::EPSILON, 1.0),
             max_inner_size: Vec2::splat(1000.0),
-            fit_rect: None,
         }
     }
 }
@@ -84,20 +81,13 @@ impl Scene {
             .ctx()
             .set_sublayer(parent_ui.layer_id(), scene_layer_id);
 
-        // let size = parent_ui.available_size_before_wrap(); // TODO: let user control via builder
-        let size = Vec2::splat(440.0);
+        let desired_outer_size = parent_ui.available_size_before_wrap();
         let (global_view_bounds, _outer_response) =
-            parent_ui.allocate_exact_size(size, Sense::hover());
+            parent_ui.allocate_exact_size(desired_outer_size, Sense::hover());
 
         let global_from_parent = TSTransform::from_translation(global_view_bounds.min.to_vec2());
         let mut to_global = global_from_parent * *to_parent;
 
-        // Optionally change the transformation so that a scene rect is
-        // contained in the view, potentially with letter boxing.
-        if let Some(rect_in_scene) = self.fit_rect {
-            // *to_parent = fit_to_rect_in_scene(global_view_bounds, rect_in_scene);
-        }
-
         let mut local_ui = parent_ui.new_child(
             UiBuilder::new()
                 .layer_id(scene_layer_id)
diff --git a/crates/egui_demo_lib/src/demo/scene.rs b/crates/egui_demo_lib/src/demo/scene.rs
index 2f11d6e6dad..e4b458648ae 100644
--- a/crates/egui_demo_lib/src/demo/scene.rs
+++ b/crates/egui_demo_lib/src/demo/scene.rs
@@ -1,6 +1,6 @@
 use egui::emath::TSTransform;
 use egui::scene::{fit_to_rect_in_scene, Scene};
-use egui::{Pos2, Rect, Sense, UiBuilder, Vec2};
+use egui::{Pos2, Rect, Vec2};
 
 use super::widget_gallery;
 
@@ -53,26 +53,31 @@ impl crate::View for SceneDemo {
         egui::Frame::group(ui.style())
             .inner_margin(0.0)
             .show(ui, |ui| {
-                let scene = Scene::new().max_inner_size([500.0, 1000.0]);
+                let scene = Scene::new().max_inner_size([350.0, 1000.0]);
 
                 let mut reset_view = false;
+                let mut inner_rect = Rect::NAN;
                 let response = scene.show(ui, &mut self.parent_from_child, |ui| {
+                    reset_view = ui.button("Reset view").clicked();
+
+                    ui.add_space(16.0);
+
                     self.widget_gallery.ui(ui);
 
-                    // ui.put(
-                    //     Rect::from_min_size(Pos2::ZERO, Vec2::splat(64.0)),
-                    //     egui::Button::new("Button"),
-                    // );
-                    // ui.put(
-                    //     Rect::from_min_size(Pos2::ZERO + 72.0 * Vec2::DOWN, Vec2::new(500.0, 64.0)),
-                    //     egui::Label::new(format!("Inner ui min_rect: {:?}", ui.min_rect())),
-                    // );
+                    ui.put(
+                        Rect::from_min_size(Pos2::new(0.0, -64.0), Vec2::new(200.0, 16.0)),
+                        egui::Label::new("You can put a widget anywhere").selectable(false),
+                    );
 
-                    reset_view = ui.button("Reset view").clicked();
+                    inner_rect = ui.min_rect();
                 });
 
                 if reset_view || response.double_clicked() {
-                    self.parent_from_child = TSTransform::from_scaling(0.5);
+                    // TODO: auto-call this on first frame?
+                    self.parent_from_child = fit_to_rect_in_scene(
+                        Rect::from_min_size(Pos2::ZERO, ui.min_size()),
+                        inner_rect,
+                    );
                 }
             });
     }