feat: auto-fit view to start region

src/app.rs

@@ -28,6 +28,18 @@ pub struct TemplateApp {
     #[serde(skip)]
     fps_ema: f32,
 
+    /// Whether we've auto-fitted the start viewport.
+    #[serde(skip)]
+    did_fit_start: bool,
+
+    /// Last known cursor position (for edge scrolling even without movement).
+    #[serde(skip)]
+    last_cursor_pos: Option<egui::Pos2>,
+
+    /// Whether a reset-to-start was requested (from UI)
+    #[serde(skip)]
+    reset_view_requested: bool,
+
     /// Last pointer position for manual drag tracking (smoother than `Sense::drag`).
     #[serde(skip)]
     last_pointer_pos: Option<egui::Pos2>,
@@ -55,6 +67,9 @@ impl Default for TemplateApp {
             last_pointer_pos: None,
             is_dragging: false,
             text_cache: None,
+            did_fit_start: false,
+            last_cursor_pos: None,
+            reset_view_requested: false,
         }
     }
 }
@@ -180,9 +195,7 @@ impl eframe::App for TemplateApp {
 
                     ui.label(format!("Zoom: {:.0}%", self.zoom * 100.0));
                     if ui.button("Reset View").clicked() {
-                        self.pan_x = 0.0;
+                        self.reset_view_requested = true;
-                        self.pan_y = 0.0;
-                        self.zoom = 1.0;
                     }
 
                     ui.separator();
@@ -214,6 +227,40 @@ impl eframe::App for TemplateApp {
             let canvas_rect = response.rect;
             painter.rect_filled(canvas_rect, 0.0, background_color);
 
+            if !self.did_fit_start {
+                self.reset_view_requested = true;
+                self.did_fit_start = true;
+            }
+
+            let mut maybe_fit_view = |rect: &egui::Rect| {
+                if let Some(ref content) = self.svg_content {
+                    if let Some((sx, sy, sw, sh)) = content.start_rect.or(content.viewbox) {
+                        if sw > 0.0 && sh > 0.0 {
+                            let scale_x = rect.width() / sw;
+                            let scale_y = rect.height() / sh;
+                            let fit_zoom = scale_x.min(scale_y).clamp(0.01, 100.0);
+                            let visible_w = rect.width() / fit_zoom;
+                            let visible_h = rect.height() / fit_zoom;
+
+                            self.zoom = fit_zoom;
+                            self.pan_x = -sx + (visible_w - sw) * 0.5;
+                            self.pan_y = -sy + (visible_h - sh) * 0.5;
+                            return true;
+                        }
+                    }
+                }
+                false
+            };
+
+            if self.reset_view_requested {
+                if maybe_fit_view(&canvas_rect) {
+                    self.reset_view_requested = false;
+                } else {
+                    // Nothing to fit, still clear the flag to avoid loops
+                    self.reset_view_requested = false;
+                }
+            }
+
             // Drag handling
             if primary_pressed && response.hovered() {
                 self.is_dragging = true;
@@ -257,8 +304,7 @@ impl eframe::App for TemplateApp {
             let internal_alpha = (0.3_f32 * 255.0).round() as u8;
             let video_scroll_color =
                 egui::Color32::from_rgba_unmultiplied(255, 0, 0, internal_alpha);
-            let audio_area_color =
+            let audio_area_color = egui::Color32::from_rgba_unmultiplied(0, 0, 255, internal_alpha);
-                egui::Color32::from_rgba_unmultiplied(0, 0, 255, internal_alpha);
             let anchor_color = egui::Color32::from_rgba_unmultiplied(64, 255, 64, internal_alpha);
             let text_color = egui::Color32::from_rgb(255, 255, 255);
 

src/svg.rs

@@ -1,7 +1,7 @@
 //! SVG parsing module for extracting special elements from SVG files.
 
-use quick_xml::Reader;
 use quick_xml::events::Event;
+use quick_xml::Reader;
 use std::fs;
 
 /// Trait for elements that can be rendered with a bounding box.
@@ -114,6 +114,7 @@ pub struct SvgContent {
     pub texts: Vec<TextElement>,
     pub viewbox: Option<(f32, f32, f32, f32)>, // (min_x, min_y, width, height)
     pub background_color: Option<[u8; 3]>,
+    pub start_rect: Option<(f32, f32, f32, f32)>,
 }
 
 /// State for tracking current element during parsing.
@@ -287,6 +288,8 @@ impl SvgContent {
                                     width,
                                     height,
                                 });
+                            } else if id == "start" {
+                                svg_content.start_rect = Some((x, y, width, height));
                             }
                         }
                         "text" => {
@@ -364,6 +367,8 @@ impl SvgContent {
                                 width,
                                 height,
                             });
+                        } else if id == "start" {
+                            svg_content.start_rect = Some((x, y, width, height));
                         }
                     }
                 }