Add buttons to scroll file editor

src/file_editor.rs

@@ -40,6 +40,12 @@ pub struct FileEditor {
     #[serde(skip)]
     inner: Option<Inner>,
 
+    /// The distance to scroll when paging up or down.
+    ///
+    /// This is calculated when the view is rendered.
+    #[serde(skip)]
+    scroll_delta: f32,
+
     /// Whether the file has been edited since it was last saved to disk.
     is_dirty: bool,
 }
@@ -89,6 +95,7 @@ impl FileEditor {
             buffer,
             file_mtime: None,
             buffer_mtime: Local::now(),
+            scroll_delta: 0.0,
             is_dirty: false,
             inner: None,
         }
@@ -162,6 +169,18 @@ impl FileEditor {
 
             const MAX_NOTE_WIDTH: f32 = 600.0;
 
+            // distance to scroll when paging up or down.
+            let mut scroll_delta = 0.0;
+
+            ui.input_mut(|input| {
+                if input.consume_key(egui::Modifiers::NONE, egui::Key::PageUp) {
+                    scroll_delta += self.scroll_delta;
+                }
+                if input.consume_key(egui::Modifiers::NONE, egui::Key::PageDown) {
+                    scroll_delta -= self.scroll_delta;
+                }
+            });
+
             ui.horizontal(|ui| {
                 ui.label("new");
                 if ui.button(" text ").clicked() {
@@ -173,9 +192,23 @@ impl FileEditor {
                     self.buffer
                         .push(BufferItem::Handwriting(Default::default()));
                 }
+
+                ui.add_space(16.0);
+
+                ui.label("scroll");
+                if ui.button("  up  ").clicked() {
+                    scroll_delta += self.scroll_delta;
+                }
+                if ui.button("down").clicked() {
+                    scroll_delta -= self.scroll_delta;
+                }
             });
 
-            ScrollArea::vertical().show(ui, |ui| {
+            let scroll_area = ScrollArea::vertical().show(ui, |ui| {
+                if scroll_delta != 0.0 {
+                    ui.scroll_with_delta(Vec2::new(0.0, scroll_delta));
+                }
+
                 ui.horizontal(|ui| {
                     let side_padding = ui.available_width().sub(MAX_NOTE_WIDTH).max(0.0).div(2.0);
                     ui.add_space(side_padding);
@@ -186,6 +219,8 @@ impl FileEditor {
                     ui.add_space(side_padding);
                 });
             });
+
+            self.scroll_delta = scroll_area.inner_rect.height() * 0.9;
         });
     }