textview: Allow zooming the text (#21)

This allows the user to change the text size via keyboard, scrolling,
zoom gesture and from the primary menu.

aardvark-app/src/aardvark.gresource.xml

@@ -2,7 +2,9 @@
 <gresources>
   <gresource prefix="/org/p2panda/aardvark">
     <file preprocess="xml-stripblanks">window.ui</file>
+    <file preprocess="xml-stripblanks">components/zoom_level_selector.ui</file>
     <file preprocess="xml-stripblanks">gtk/help-overlay.ui</file>
     <file compressed="true" alias="style.css">style.css</file>
   </gresource>
 </gresources>
+

aardvark-app/src/components/mod.rs

@@ -0,0 +1,3 @@
+mod zoom_level_selector;
+
+pub use self::zoom_level_selector::ZoomLevelSelector;

aardvark-app/src/components/zoom_level_selector.rs

@@ -0,0 +1,81 @@
+/* zoom_level_selector.rs
+ *
+ * Copyright 2025 Julian Sparber <[email protected]>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+use std::cell::Cell;
+
+use adw::subclass::prelude::*;
+use gtk::prelude::*;
+use gtk::glib;
+use sourceview::*;
+
+mod imp {
+    use super::*;
+
+    #[derive(Debug, Default, glib::Properties, gtk::CompositeTemplate)]
+    #[properties(wrapper_type = super::ZoomLevelSelector)]
+    #[template(resource = "/org/p2panda/aardvark/components/zoom_level_selector.ui")]
+    pub struct ZoomLevelSelector {
+        #[template_child]
+        pub button: TemplateChild<gtk::Button>,
+        #[property(get, set)]
+        zoom_level: Cell<f64>,
+    }
+
+    #[glib::object_subclass]
+    impl ObjectSubclass for ZoomLevelSelector {
+        const NAME: &'static str = "ZoomLevelSelector";
+        type Type = super::ZoomLevelSelector;
+        type ParentType = gtk::Box;
+
+        fn class_init(klass: &mut Self::Class) {
+            klass.bind_template();
+        }
+
+        fn instance_init(obj: &glib::subclass::InitializingObject<Self>) {
+            obj.init_template();
+        }
+    }
+
+    #[glib::derived_properties]
+    impl ObjectImpl for ZoomLevelSelector {
+        fn constructed(&self) {
+            self.parent_constructed();
+            self.obj()
+                .bind_property("zoom_level", &*self.button, "label")
+                .sync_create()
+                .transform_to(|_, zoom_level: f64| Some(format!("{:.0}%", zoom_level * 100.0)))
+                .build();
+        }
+    }
+
+    impl WidgetImpl for ZoomLevelSelector {}
+    impl BoxImpl for ZoomLevelSelector {}
+}
+
+glib::wrapper! {
+    pub struct ZoomLevelSelector(ObjectSubclass<imp::ZoomLevelSelector>)
+        @extends gtk::Widget, gtk::Box;
+}
+
+impl ZoomLevelSelector {
+    pub fn new() -> Self {
+        glib::Object::builder()
+            .build()
+    }
+}

aardvark-app/src/components/zoom_level_selector.ui

@@ -0,0 +1,57 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<interface>
+  <requires lib="gtk" version="4.0"/>
+  <template class="ZoomLevelSelector" parent="GtkBox">
+    <property name="hexpand">True</property>
+    <child>
+      <object class="GtkBox">
+        <property name="spacing">12</property>
+        <property name="margin-start">18</property>
+        <property name="margin-end">18</property>
+        <child>
+          <object class="GtkButton">
+            <property name="icon-name">zoom-out-symbolic</property>
+            <!-- Translators: Button tooltip-->
+            <property name="tooltip-text" translatable="yes">Zoom Out</property>
+            <property name="action-name">window.zoom-out</property>
+            <accessibility>
+              <!-- Translators: Button -->
+              <property name="label" translatable="yes">Zoom Out</property>
+            </accessibility>
+            <style>
+              <class name="circular"/>
+              <class name="flat"/>
+            </style>
+          </object>
+        </child>
+        <child>
+          <object class="GtkButton" id="button">
+            <property name="hexpand">True</property>
+            <property name="action-name">window.zoom-one</property>
+            <style>
+              <class name="circular"/>
+              <class name="flat"/>
+            </style>
+          </object>
+        </child>
+        <child>
+          <object class="GtkButton">
+            <property name="icon-name">zoom-in-symbolic</property>
+            <!-- Translators: Button tooltip-->
+            <property name="tooltip-text" translatable="yes">Zoom In</property>
+            <property name="action-name">window.zoom-in</property>
+            <accessibility>
+              <!-- Translators: Button -->
+              <property name="label" translatable="yes">Zoom In</property>
+            </accessibility>
+            <style>
+              <class name="circular"/>
+              <class name="flat"/>
+            </style>
+          </object>
+        </child>
+      </object>
+    </child>
+  </template>
+</interface>
+

aardvark-app/src/main.rs

@@ -20,6 +20,7 @@
 
 mod application;
 mod config;
+mod components;
 mod document;
 mod textbuffer;
 mod window;

aardvark-app/src/style.css

@@ -13,7 +13,3 @@
 .user-counter {
   font-weight: bold;
 }
-
-.editor {
-  font-size: 24px;
-}

aardvark-app/src/window.rs

@@ -18,18 +18,23 @@
  * SPDX-License-Identifier: GPL-3.0-or-later
  */
 
+use std::cell;
+
 use adw::prelude::AdwDialogExt;
 use adw::subclass::prelude::*;
 use gtk::prelude::*;
-use gtk::{gio, glib};
+use gtk::{gio, glib, gdk};
 use sourceview::*;
 
-use crate::AardvarkTextBuffer;
+use crate::{AardvarkTextBuffer, components::ZoomLevelSelector};
+
+const BASE_TEXT_FONT_SIZE: f64 = 24.0;
 
 mod imp {
     use super::*;
 
-    #[derive(Debug, Default, gtk::CompositeTemplate)]
+    #[derive(Debug, Default, glib::Properties, gtk::CompositeTemplate)]
+    #[properties(wrapper_type = super::AardvarkWindow)]
     #[template(resource = "/org/p2panda/aardvark/window.ui")]
     pub struct AardvarkWindow {
         // Template widgets
@@ -41,6 +46,12 @@ mod imp {
         pub open_document_dialog: TemplateChild<adw::Dialog>,
         #[template_child]
         pub toast_overlay: TemplateChild<adw::ToastOverlay>,
+        pub css_provider: gtk::CssProvider,
+        pub font_size: cell::Cell<f64>,
+        #[property(get, set = Self::set_font_scale, default = 0.0)]
+        pub font_scale: cell::Cell<f64>,
+        #[property(get, default = 1.0)]
+        pub zoom_level: cell::Cell<f64>,
     }
 
     #[glib::object_subclass]
@@ -50,21 +61,99 @@ mod imp {
         type ParentType = adw::ApplicationWindow;
 
         fn class_init(klass: &mut Self::Class) {
+            ZoomLevelSelector::static_type();
+
             klass.bind_template();
+
+            klass.install_action("window.zoom-in", None, |window, _, _| {
+                window.set_font_scale(window.font_scale() + 1.0);
+            });
+            klass.install_action("window.zoom-out", None, |window, _, _| {
+                window.set_font_scale(window.font_scale() - 1.0);
+            });
+            klass.install_action("window.zoom-one", None, |window, _, _| {
+                window.set_font_scale(0.0);
+            });
+
+            klass.add_binding_action(gdk::Key::plus,
+                                     gdk::ModifierType::CONTROL_MASK,
+                                     "window.zoom-in");
+            klass.add_binding_action(gdk::Key::KP_Add,
+                                     gdk::ModifierType::CONTROL_MASK,
+                                     "window.zoom-in");
+            klass.add_binding_action(gdk::Key::minus,
+                                     gdk::ModifierType::CONTROL_MASK,
+                                     "window.zoom-out");
+            // gnome-text-editor uses this as well: probably to make it
+            // nicer for the US keyboard layout
+            klass.add_binding_action(gdk::Key::equal,
+                                     gdk::ModifierType::CONTROL_MASK,
+                                     "window.zoom-out");
+            klass.add_binding_action(gdk::Key::KP_Subtract,
+                                     gdk::ModifierType::CONTROL_MASK,
+                                     "window.zoom-out");
+            klass.add_binding_action(gdk::Key::_0,
+                                     gdk::ModifierType::CONTROL_MASK,
+                                     "window.zoom-one");
+            klass.add_binding_action(gdk::Key::KP_0,
+                                     gdk::ModifierType::CONTROL_MASK,
+                                     "window.zoom-one");
         }
 
         fn instance_init(obj: &glib::subclass::InitializingObject<Self>) {
             obj.init_template();
         }
     }
 
+    #[glib::derived_properties]
     impl ObjectImpl for AardvarkWindow {
         fn constructed(&self) {
             self.parent_constructed();
 
             let buffer = AardvarkTextBuffer::new();
             self.text_view.set_buffer(Some(&buffer));
 
+            self.font_size.set(BASE_TEXT_FONT_SIZE);
+            self.obj().set_font_scale(0.0);
+            gtk::style_context_add_provider_for_display (
+                &self.obj().display(),
+                &self.css_provider,
+                gtk::STYLE_PROVIDER_PRIORITY_APPLICATION);
+
+            let scroll_controller = gtk::EventControllerScroll::new(gtk::EventControllerScrollFlags::VERTICAL);
+            scroll_controller.set_propagation_phase(gtk::PropagationPhase::Capture);
+            let window = self.obj().clone();
+            scroll_controller.connect_scroll(move |scroll, _dx, dy| {
+                if scroll.current_event_state().contains(gdk::ModifierType::CONTROL_MASK) {
+                    if dy < 0.0 {
+                        window.set_font_scale(window.font_scale() + 1.0);
+                    } else {
+                        window.set_font_scale(window.font_scale() - 1.0);
+                    }
+                    glib::Propagation::Stop
+                } else {
+                    glib::Propagation::Proceed
+                }
+            });
+            self.obj().add_controller(scroll_controller);
+
+            let zoom_gesture = gtk::GestureZoom::new();
+            let window = self.obj().clone();
+            let prev_delta = std::cell::Cell::new(0.0);
+            zoom_gesture.connect_scale_changed(move |_, delta| {
+                if prev_delta.get() == delta {
+                    return;
+                }
+
+                if prev_delta.get() < delta {
+                    window.set_font_scale(window.font_scale() + delta);
+                } else {
+                    window.set_font_scale(window.font_scale() - delta);
+                }
+                prev_delta.set(delta);
+            });
+            self.obj().add_controller(zoom_gesture);
+
             let window = self.obj().clone();
             let dialog = self.open_document_dialog.clone();
             self.open_document_button.connect_clicked(move |_| {
@@ -73,6 +162,20 @@ mod imp {
         }
     }
 
+    impl AardvarkWindow {
+        fn set_font_scale(&self, value: f64) {
+            let font_size = self.font_size.get();
+
+            self.font_scale.set(value);
+
+            let size = (font_size + self.obj().font_scale()).max(1.0);
+            self.zoom_level.set(size / font_size);
+            self.obj().notify_zoom_level();
+            self.css_provider.load_from_string(&format!( ".sourceview {{ font-size: {size}px; }}"));
+            self.obj().action_set_enabled("window.zoom-out", size > 1.0);
+        }
+    }
+
     impl WidgetImpl for AardvarkWindow {}
     impl WindowImpl for AardvarkWindow {}
     impl ApplicationWindowImpl for AardvarkWindow {}