From 238581c65e4b0880a2bc5d0858e4dfe3e48e8899 Mon Sep 17 00:00:00 2001
From: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>
Date: Tue, 28 Dec 2021 20:54:26 +0100
Subject: [PATCH] wip

---
 egui/src/context.rs | 60 ++++++++++++++++++++++++++++++++++++++++++++-
 egui/src/layout.rs  | 12 +++++++++
 egui/src/lib.rs     |  2 ++
 egui/src/ui.rs      |  7 +++++-
 4 files changed, 79 insertions(+), 2 deletions(-)

diff --git a/egui/src/context.rs b/egui/src/context.rs
index f9617848..27f3ad8e 100644
--- a/egui/src/context.rs
+++ b/egui/src/context.rs
@@ -19,6 +19,15 @@ use epaint::{stats::*, text::Fonts, *};
 
 // ----------------------------------------------------------------------------
 
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum PassState {
+    SinglePass,
+    SizePass,
+    LayoutPass,
+}
+
+// ----------------------------------------------------------------------------
+
 /// A wrapper around [`Arc`](std::sync::Arc)`<`[`Context`]`>`.
 /// This is how you will normally create and access a [`Context`].
 ///
@@ -103,7 +112,7 @@ impl CtxRef {
     pub fn run(
         &mut self,
         new_raw_input: RawInput,
-        mut run_ui: impl FnMut(&CtxRef),
+        run_ui: impl Fn(&CtxRef),
     ) -> (Output, Vec<ClippedShape>) {
         self.memory().begin_frame(&self.input, &new_raw_input);
 
@@ -126,6 +135,48 @@ impl CtxRef {
             },
         );
 
+        if self.memory().options.multi_pass {
+            self.frame_state.lock().begin_pass(&self.input);
+            self.mutate(|context| {
+                context.pass_state = Some(PassState::SizePass);
+            });
+
+            run_ui(self);
+
+            self.drain_paint_lists();
+            self.mutate(|context| {
+                context.input.on_events(new_raw_input);
+                context.pass_state = Some(PassState::LayoutPass);
+            });
+
+            self.frame_state.lock().begin_pass(&self.input);
+            run_ui(self);
+        } else {
+            self.mutate(|context| {
+                context.input.on_events(new_raw_input);
+                context.pass_state = Some(PassState::SinglePass);
+            });
+        }
+
+        self.mutate(|context| {
+            if let Some(new_pixels_per_point) = context.memory.lock().new_pixels_per_point.take() {
+                context.input.pixels_per_point = new_pixels_per_point;
+            }
+            context.input.begin_frame(&new_raw_input);
+            context.update_fonts(context.input.pixels_per_point());
+        });
+
+        // Ensure we register the background area so panels and background ui can catch clicks:
+        let screen_rect = self.input.screen_rect();
+        self.memory().areas.set_state(
+            LayerId::background(),
+            containers::area::State {
+                pos: screen_rect.min,
+                size: screen_rect.size(),
+                interactable: true,
+            },
+        );
+
         if self.memory().options.multi_pass {
             self.frame_state.lock().begin_pass(&self.input);
             run_ui(self);
@@ -142,6 +193,10 @@ impl CtxRef {
             run_ui(self);
         }
 
+        self.mutate(|context| {
+            context.pass_state = None;
+        });
+
         self.end_frame()
     }
 
@@ -392,6 +447,8 @@ pub struct Context {
 
     /// While positive, keep requesting repaints. Decrement at the end of each frame.
     repaint_requests: AtomicU32,
+
+    pub(crate) pass_state: Option<PassState>,
 }
 
 impl Clone for Context {
@@ -407,6 +464,7 @@ impl Clone for Context {
             output: self.output.clone(),
             paint_stats: self.paint_stats.clone(),
             repaint_requests: self.repaint_requests.load(SeqCst).into(),
+            pass_state: None,
         }
     }
 }
diff --git a/egui/src/layout.rs b/egui/src/layout.rs
index 433242ca..9f3ebf67 100644
--- a/egui/src/layout.rs
+++ b/egui/src/layout.rs
@@ -230,6 +230,18 @@ impl Layout {
         }
     }
 
+    /// change layout to one suitable for size pass
+    pub(crate) fn for_size_pass(self) -> Self {
+        Self {
+            main_dir: self.main_dir,
+            main_wrap: self.main_wrap,
+            main_align: Align::Min,
+            main_justify: false,
+            cross_align: Align::Min,
+            cross_justify: false,
+        }
+    }
+
     #[inline(always)]
     pub fn with_main_wrap(self, main_wrap: bool) -> Self {
         Self { main_wrap, ..self }
diff --git a/egui/src/lib.rs b/egui/src/lib.rs
index dc9cc561..aeebc906 100644
--- a/egui/src/lib.rs
+++ b/egui/src/lib.rs
@@ -396,6 +396,8 @@ pub mod text {
     };
 }
 
+pub(crate) use context::PassState;
+
 pub use {
     containers::*,
     context::{Context, CtxRef},
diff --git a/egui/src/ui.rs b/egui/src/ui.rs
index cbaba6f6..27fff8be 100644
--- a/egui/src/ui.rs
+++ b/egui/src/ui.rs
@@ -92,10 +92,15 @@ impl Ui {
     pub fn child_ui_with_id_source(
         &mut self,
         max_rect: Rect,
-        layout: Layout,
+        mut layout: Layout,
         id_source: impl Hash,
     ) -> Self {
         crate::egui_assert!(!max_rect.any_nan());
+
+        if self.ctx().pass_state == Some(PassState::SizePass) {
+            layout = layout.for_size_pass();
+        }
+
         let next_auto_id_source = Id::new(self.next_auto_id_source).with("child").value();
         self.next_auto_id_source = self.next_auto_id_source.wrapping_add(1);
         let menu_state = self.get_menu_state();