printing: Add printing support

Part-of: <https://gitlab.gnome.org/Incubator/loupe/-/merge_requests/165>

src/widgets/print_preview.rs

@@ -0,0 +1,122 @@
+//! Print preview widget that shows a fake page with the image on it
+
+use crate::deps::*;
+use crate::widgets::LpPrint;
+
+use adw::subclass::prelude::*;
+use glib::Properties;
+use gtk::prelude::*;
+use once_cell::sync::OnceCell;
+
+mod imp {
+    use super::*;
+
+    #[derive(Debug, Default, Properties)]
+    #[properties(wrapper_type = super::LpPrintPreview)]
+    pub struct LpPrintPreview {
+        #[property(get, set)]
+        print: OnceCell<LpPrint>,
+    }
+
+    #[glib::object_subclass]
+    impl ObjectSubclass for LpPrintPreview {
+        const NAME: &'static str = "LpPrintPreview";
+        type Type = super::LpPrintPreview;
+        type ParentType = gtk::Widget;
+    }
+
+    impl ObjectImpl for LpPrintPreview {
+        fn constructed(&self) {
+            self.parent_constructed();
+            self.obj().set_halign(gtk::Align::Center);
+            self.obj().set_valign(gtk::Align::Start);
+            self.obj().set_overflow(gtk::Overflow::Hidden);
+        }
+
+        fn properties() -> &'static [glib::ParamSpec] {
+            Self::derived_properties()
+        }
+        fn set_property(&self, id: usize, value: &glib::Value, pspec: &glib::ParamSpec) {
+            self.derived_set_property(id, value, pspec)
+        }
+        fn property(&self, id: usize, pspec: &glib::ParamSpec) -> glib::Value {
+            self.derived_property(id, pspec)
+        }
+    }
+
+    impl WidgetImpl for LpPrintPreview {
+        fn measure(&self, orientation: gtk::Orientation, _for_size: i32) -> (i32, i32, i32, i32) {
+            let (width, height) = self.display_paper_dimensions();
+
+            let size = match orientation {
+                gtk::Orientation::Horizontal => width,
+                _ => height,
+            };
+
+            (size, size, -1, -1)
+        }
+
+        fn snapshot(&self, snapshot: &gtk::Snapshot) {
+            let obj = self.obj();
+
+            snapshot.save();
+
+            let scale = obj.print().user_scale() * self.display_scale();
+            let margin_left = obj.print().user_margin_left() * self.display_scale();
+            let margin_top = obj.print().user_margin_top() * self.display_scale();
+
+            if let Some(texture) = self.obj().print().image().print_data(scale) {
+                let area = graphene::Rect::new(
+                    margin_left as f32,
+                    margin_top as f32,
+                    texture.width() as f32,
+                    texture.height() as f32,
+                );
+
+                snapshot.append_texture(&texture, &area);
+
+                // Border around image
+                snapshot.append_inset_shadow(
+                    &gsk::RoundedRect::from_rect(area, 0.),
+                    &gdk::RGBA::new(0., 0., 0., 0.3),
+                    0.,
+                    0.,
+                    1.,
+                    0.,
+                );
+            }
+            snapshot.restore();
+        }
+    }
+
+    impl LpPrintPreview {
+        /// Returns scale factor from print pixel to preview size
+        fn display_scale(&self) -> f64 {
+            let print = self.obj().print();
+
+            let height = print.page_setup().paper_height(gtk::Unit::Inch) * print.dpi();
+            let width = print.page_setup().paper_width(gtk::Unit::Inch) * print.dpi();
+
+            300. / f64::max(width, height)
+        }
+
+        /// Returns total preview size in pixels
+        fn display_paper_dimensions(&self) -> (i32, i32) {
+            let print = self.obj().print();
+
+            let height = print.page_setup().paper_height(gtk::Unit::Inch) * print.dpi();
+            let width = print.page_setup().paper_width(gtk::Unit::Inch) * print.dpi();
+
+            let scale = self.display_scale();
+
+            ((width * scale) as i32, (height * scale) as i32)
+        }
+    }
+}
+glib::wrapper! {
+    pub struct LpPrintPreview(ObjectSubclass<imp::LpPrintPreview>)
+        @extends gtk::Widget;
+}
+
+#[gtk::template_callbacks]
+impl LpPrintPreview {}