Fix preferred size of the Window with a layout

A few problem:
 - the horizontal and vertical property were swapped
 - The implementation of the "preferred_xxx" property was not materialized properly
   because the `bindings` were borrowed in the materialize_fake_properties pass
 - Since the Window has a stretch factor of 0., the preferred size of the inner layout
   was not taken into account when merging the LayoutInfo.  I believe taking the
   maximum preferred size is the right solution when merging them.

api/sixtyfps-cpp/include/sixtyfps.h

@@ -321,22 +321,11 @@ using cbindgen_private::sixtyfps_solve_path_layout;
 inline LayoutInfo LayoutInfo::merge(const LayoutInfo &other) const
 {
     // Note: This "logic" is duplicated from LayoutInfo::merge in layout.rs.
-    const auto merge_preferred_size = [](float left_stretch, float left_size, float right_stretch,
-                                         float right_size) -> float {
-        if (left_stretch < right_stretch) {
-            return left_size;
-        } else if (left_stretch > right_stretch) {
-            return right_size;
-        } else {
-            return (left_size + right_size) / 2.;
-        }
-    };
     return LayoutInfo { std::max(min, other.min),
                         std::min(max, other.max),
                         std::max(min_percent, other.min_percent),
                         std::min(max_percent, other.max_percent),
-                        merge_preferred_size(stretch, preferred,
-                                             other.stretch, other.preferred),
+                        std::max(preferred, other.preferred),
                         std::min(stretch, other.stretch) };
 }
 

sixtyfps_compiler/passes/default_geometry.rs

@@ -146,18 +146,18 @@ fn gen_layout_info_prop(elem: &ElementRc) {
         "layoutinfo_h",
         crate::layout::layout_info_type(),
     );
-    elem.borrow_mut().layout_info_prop = Some((li_v.clone(), li_h.clone()));
+    elem.borrow_mut().layout_info_prop = Some((li_h.clone(), li_v.clone()));
     let mut expr_h = implicit_layout_info_call(elem, Orientation::Horizontal);
     let mut expr_v = implicit_layout_info_call(elem, Orientation::Vertical);
 
     for child_info in child_infos {
-        expr_v = Expression::BinaryExpression {
-            lhs: Box::new(std::mem::take(&mut expr_v)),
+        expr_h = Expression::BinaryExpression {
+            lhs: Box::new(std::mem::take(&mut expr_h)),
             rhs: Box::new(Expression::PropertyReference(child_info.0)),
             op: '+',
         };
-        expr_h = Expression::BinaryExpression {
-            lhs: Box::new(std::mem::take(&mut expr_h)),
+        expr_v = Expression::BinaryExpression {
+            lhs: Box::new(std::mem::take(&mut expr_v)),
             rhs: Box::new(Expression::PropertyReference(child_info.1)),
             op: '+',
         };

sixtyfps_compiler/passes/materialize_fake_properties.rs

@@ -20,17 +20,17 @@ use std::collections::HashMap;
 use std::rc::Rc;
 
 pub fn materialize_fake_properties(component: &Rc<Component>) {
+    let mut to_initialize = std::collections::HashSet::new();
+
     recurse_elem_including_sub_components_no_borrow(component, &(), &mut |elem, _| {
         visit_all_named_references_in_element(elem, |nr| {
             let elem = nr.element();
-            let must_initialize = {
             let mut elem = elem.borrow_mut();
             let elem = &mut *elem;
-                maybe_materialize(&mut elem.property_declarations, &elem.base_type, nr.name())
+            if maybe_materialize(&mut elem.property_declarations, &elem.base_type, nr.name())
                 && !elem.bindings.contains_key(nr.name())
-            };
-            if must_initialize {
-                initialize(elem, nr.name());
+            {
+                to_initialize.insert(nr.clone());
             }
         });
         let mut elem = elem.borrow_mut();
@@ -38,7 +38,14 @@ pub fn materialize_fake_properties(component: &Rc<Component>) {
         for prop in elem.bindings.keys() {
             maybe_materialize(&mut elem.property_declarations, &elem.base_type, prop);
         }
-    })
+    });
+
+    for nr in to_initialize {
+        let elem = nr.element();
+        if !elem.borrow().bindings.contains_key(nr.name()) {
+            initialize(elem, nr.name())
+        }
+    }
 }
 
 fn maybe_materialize(

sixtyfps_runtime/corelib/layout.rs

@@ -59,27 +59,12 @@ impl Default for LayoutInfo {
 impl LayoutInfo {
     // Note: This "logic" is duplicated in the cpp generator's generated code for merging layout infos.
     pub fn merge(&self, other: &LayoutInfo) -> Self {
-        let merge_preferred_size = |left_stretch, left_size, right_stretch, right_size| {
-            if left_stretch < right_stretch {
-                left_size
-            } else if left_stretch > right_stretch {
-                right_size
-            } else {
-                (left_size + right_size) / 2.
-            }
-        };
-
         Self {
             min: self.min.max(other.min),
             max: self.max.min(other.max),
             min_percent: self.min_percent.max(other.min_percent),
             max_percent: self.max_percent.min(other.max_percent),
-            preferred: merge_preferred_size(
-                self.stretch,
-                self.preferred,
-                other.stretch,
-                other.preferred,
-            ),
+            preferred: self.preferred.max(other.preferred),
             stretch: self.stretch.min(other.stretch),
         }
     }

tests/cases/layout/window_preferred.60

@@ -0,0 +1,51 @@
+/* LICENSE BEGIN
+    This file is part of the SixtyFPS Project -- https://sixtyfps.io
+    Copyright (c) 2020 Olivier Goffart <olivier.goffart@sixtyfps.io>
+    Copyright (c) 2020 Simon Hausmann <simon.hausmann@sixtyfps.io>
+
+    SPDX-License-Identifier: GPL-3.0-only
+    This file is also available under commercial licensing terms.
+    Please contact info@sixtyfps.io for more information.
+LICENSE END */
+TestCase := Window {
+    VerticalLayout {
+        padding: 10px;
+        spacing: 27px;
+        Rectangle {
+            background: blue;
+            preferred-width: 25phx;
+            preferred-height: 500phx;
+            horizontal-stretch: 0;
+            vertical-stretch: 0;
+        }
+        Rectangle {
+            background: green;
+            // implicit: horizontal-stretch: 1
+        }
+    }
+
+    property w <=> root.preferred-width;
+
+    property <bool> test: root.preferred_height == 500phx + 20px + 27px && root.preferred_width == 25phx + 20px;
+}
+
+/*
+
+```cpp
+auto handle = TestCase::create();
+const TestCase &instance = *handle;
+assert(instance.get_test());
+```
+
+
+```rust
+let instance = TestCase::new();
+assert!(instance.get_test());
+```
+
+```js
+var instance = new sixtyfps.TestCase();
+assert(instance.test);
+```
+
+*/