Polish of the rotation feature

- Add a check that this only Applies to Image element without children
 - Default the origin to the center of the Image
 - Add docs and test

cc: #1481

internal/compiler/passes.rs

@@ -6,6 +6,7 @@ mod binding_analysis;
 mod check_aliases;
 mod check_expressions;
 mod check_public_api;
+mod check_rotation;
 mod clip;
 mod collect_custom_fonts;
 mod collect_globals;
@@ -42,9 +43,11 @@ mod unique_id;
 mod visible;
 mod z_order;
 
-use std::{collections::HashSet, rc::Rc};
-
+use crate::expression_tree::Expression;
 use crate::langtype::Type;
+use crate::namedreference::NamedReference;
+use std::collections::HashSet;
+use std::rc::Rc;
 
 pub async fn run_passes(
     doc: &crate::object_tree::Document,
@@ -75,6 +78,7 @@ pub async fn run_passes(
     infer_aliases_types::resolve_aliases(doc, diag);
     resolving::resolve_expressions(doc, type_loader, diag);
     check_expressions::check_expressions(doc, diag);
+    check_rotation::check_rotation(doc, diag);
     unique_id::check_unique_id(doc, diag);
     check_public_api::check_public_api(doc, diag);
 
@@ -128,6 +132,7 @@ pub async fn run_passes(
             component,
             "opacity",
             core::iter::empty(),
+            None,
             "Opacity",
             &global_type_registry.borrow(),
             diag,
@@ -136,6 +141,7 @@ pub async fn run_passes(
             component,
             "cache-rendering-hint",
             core::iter::empty(),
+            None,
             "Layer",
             &global_type_registry.borrow(),
             diag,
@@ -147,6 +153,20 @@ pub async fn run_passes(
             crate::typeregister::RESERVED_ROTATION_PROPERTIES[1..]
                 .iter()
                 .map(|(prop_name, _)| *prop_name),
+            Some(&|e, prop| Expression::BinaryExpression {
+                lhs: Expression::PropertyReference(NamedReference::new(
+                    e,
+                    match prop {
+                        "rotation-origin-x" => "width",
+                        "rotation-origin-y" => "height",
+                        "rotation-angle" => return Expression::Invalid,
+                        _ => unreachable!(),
+                    },
+                ))
+                .into(),
+                op: '/',
+                rhs: Expression::NumberLiteral(2., Default::default()).into(),
+            }),
             "Rotate",
             &global_type_registry.borrow(),
             diag,
@@ -244,5 +264,6 @@ pub fn run_import_passes(
     infer_aliases_types::resolve_aliases(doc, diag);
     resolving::resolve_expressions(doc, type_loader, diag);
     check_expressions::check_expressions(doc, diag);
+    check_rotation::check_rotation(doc, diag);
     unique_id::check_unique_id(doc, diag);
 }

internal/compiler/passes/check_rotation.rs

@@ -0,0 +1,51 @@
+// Copyright © SixtyFPS GmbH <info@slint-ui.com>
+// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-commercial
+
+use crate::diagnostics::BuildDiagnostics;
+use crate::diagnostics::Spanned;
+use crate::langtype::Type;
+use crate::object_tree::Element;
+
+/// Check that the rotation is only on Image
+pub fn check_rotation(doc: &crate::object_tree::Document, diag: &mut BuildDiagnostics) {
+    for cmp in &doc.inner_components {
+        crate::object_tree::recurse_elem_including_sub_components(cmp, &(), &mut |elem, _| {
+            let e = elem.borrow();
+            if crate::typeregister::RESERVED_ROTATION_PROPERTIES
+                .iter()
+                .any(|(property_name, _)| is_property_set(&*e, *&property_name))
+            {
+                if matches!(e.native_class(), Some(native) if native.class_name != "ClippedImage") {
+                    let span = e
+                        .bindings
+                        .get("rotation-angle")
+                        .and_then(|e| e.borrow().span.clone())
+                        .unwrap_or_else(|| e.to_source_location());
+
+                    diag.push_error_with_span(
+                        "rotation properties can only be applied to the Image element".into(),
+                        span,
+                    );
+                } else if has_any_children(&*e) {
+                    diag.push_error_with_span(
+                        "Elements with rotation properties cannot have children elements".into(),
+                        e.to_source_location(),
+                    );
+                }
+            }
+        });
+    }
+}
+
+/// Returns true if this element or its base have any children.
+fn has_any_children(e: &Element) -> bool {
+    !e.children.is_empty()
+        || matches!(&e.base_type, Type::Component(base) if has_any_children(&base.root_element.borrow()))
+}
+
+/// Returns true if the property is set.
+fn is_property_set(e: &Element, property_name: &str) -> bool {
+    e.bindings.contains_key(property_name)
+        || e.property_analysis.borrow().get(property_name).map_or(false, |a| a.is_set)
+        || matches!(&e.base_type, Type::Component(base) if is_property_set(&base.root_element.borrow(), property_name))
+}

internal/compiler/passes/lower_property_to_element.rs

@@ -8,20 +8,20 @@ use std::cell::RefCell;
 use std::rc::Rc;
 
 use crate::diagnostics::BuildDiagnostics;
-use crate::expression_tree::{BindingExpression, NamedReference};
+use crate::expression_tree::{BindingExpression, Expression, NamedReference};
 use crate::langtype::Type;
 use crate::object_tree::{self, Component, Element, ElementRc};
 use crate::typeregister::TypeRegister;
 
-// If any element in `component` declares a binding to the first property in `properties`, then a new
-// element of type `element_name` is created, injected as a parent to the element and bindings to all
-// remaining properties in `properties` are mapped. This way for example ["rotation-angle", "rotation-origin-x", "rotation-origin-y"]
-// creates a `Rotate` element when `rotation-angle` is used and any optional `rotation-origin-*` bindings are redirected to the
-// `Rotate` element.
+/// If any element in `component` declares a binding to `property_name`, then a new
+/// element of type `element_name` is created, injected as a parent to the element and bindings
+/// to property_name and all properties in  extra_properties are mapped.
+/// Default balue for the property extra_properties is queried witht the `default_value_for_extra_properties`
 pub(crate) fn lower_property_to_element(
     component: &Rc<Component>,
     property_name: &'static str,
     extra_properties: impl Iterator<Item = &'static str> + Clone,
+    default_value_for_extra_properties: Option<&dyn Fn(&ElementRc, &str) -> Expression>,
     element_name: &str,
     type_register: &TypeRegister,
     diag: &mut BuildDiagnostics,
@@ -67,6 +67,7 @@ pub(crate) fn lower_property_to_element(
                             &root_elem,
                             property_name,
                             extra_properties.clone(),
+                            default_value_for_extra_properties,
                             element_name,
                             type_register,
                         ),
@@ -77,6 +78,7 @@ pub(crate) fn lower_property_to_element(
                     &child,
                     property_name,
                     extra_properties.clone(),
+                    default_value_for_extra_properties,
                     element_name,
                     type_register,
                 );
@@ -94,6 +96,7 @@ fn create_property_element(
     child: &ElementRc,
     property_name: &'static str,
     extra_properties: impl Iterator<Item = &'static str>,
+    default_value_for_extra_properties: Option<&dyn Fn(&ElementRc, &str) -> Expression>,
     element_name: &str,
     type_register: &TypeRegister,
 ) -> ElementRc {
@@ -107,7 +110,12 @@ fn create_property_element(
                         .into(),
                 ))
             } else {
-                None
+                default_value_for_extra_properties.map(|f| {
+                    (
+                        property_name.to_string(),
+                        BindingExpression::from(f(child, property_name)).into(),
+                    )
+                })
             }
         })
         .collect();

internal/compiler/tests/syntax/basic/rotation.slint

@@ -0,0 +1,64 @@
+// Copyright © SixtyFPS GmbH <info@slint-ui.com>
+// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-commercial
+
+Ex1 := Rectangle {
+    Rectangle {
+        rotation-origin-x: width / 2;
+        rotation-angle: 45deg;
+//                     ^error{rotation properties can only be applied to the Image element}
+        rotation-origin-y: width / 2;
+    }
+    Rectangle {
+//  ^error{rotation properties can only be applied to the Image element}
+        rotation-origin-x: width / 2;
+        rotation-origin-y: width / 2;
+    }
+}
+
+RotImg := Image {
+    rotation-angle: 45deg;
+}
+
+JustAnImage := Image {}
+
+ImageWithChild := Image {
+    Rectangle {}
+}
+
+Ex2 := Rectangle {
+    Image {
+//  ^error{Elements with rotation properties cannot have children elements}
+        rotation-angle: 45deg;
+        Rectangle {}
+    }
+    RotImg { 
+//  ^error{Elements with rotation properties cannot have children elements}
+        Rectangle {}
+    }
+    ImageWithChild {
+//  ^error{Elements with rotation properties cannot have children elements}
+        rotation-origin-x: 45px;
+    }
+    JustAnImage {
+//  ^error{Elements with rotation properties cannot have children elements}
+        rotation-angle: 45deg;
+        Rectangle {}
+    }
+}
+
+
+Ex3 := Rectangle {
+    i1 := Image {
+//       ^error{Elements with rotation properties cannot have children elements}
+        Rectangle {}
+    }
+    i2 := Rectangle {}
+//       ^error{rotation properties can only be applied to the Image element}
+
+    TouchArea {
+        clicked => {
+            i1.rotation-angle = 60deg;
+            i2.rotation-origin-x = 10px;
+        }
+    }
+}