Implement two page drawing

src/ui.rs

@@ -47,7 +47,18 @@ pub fn toggle_fullscreen(ui: &Ui) {
 
 fn update_page_status(ui: &Ui) {
     let page_status = match &ui.document_canvas {
-        Some(doc) => format!("{} / {}", doc.current_page_number, doc.num_pages),
+        Some(doc) => {
+            if doc.num_pages == 1 {
+                format!("{} / {}", doc.current_page_number, doc.num_pages)
+            } else {
+                format!(
+                    "{}-{} / {}",
+                    doc.current_page_number,
+                    doc.current_page_number + 1,
+                    doc.num_pages
+                )
+            }
+        }
         None => "No document loaded!".to_string(),
     };
     ui.page_indicator.set_label(page_status.as_str());
@@ -63,7 +74,8 @@ fn process_touch(ui: &mut Ui, x: f64, y: f64) {
     let center = ui.drawing_area.width() / 2;
     if y < (ui.drawing_area.height() / 5) as f64 {
         toggle_fullscreen(ui);
-    } else if x > center as f64 && doc.current_page_number < doc.num_pages {
+    } else if x > center as f64 && doc.current_page_number < doc.num_pages - 1 {
+        // Do not load last page since showing two pages would result in error
         doc.current_page_number += 1;
     } else if x < center as f64 && doc.current_page_number > 1 {
         doc.current_page_number -= 1;
@@ -87,7 +99,12 @@ impl Ui {
             bottom_bar: Box::builder().hexpand_set(true).build(),
             header_bar: HeaderBar::builder().build(),
             page_indicator: Label::builder().build(),
-            drawing_area: DrawingArea::builder().hexpand(true).vexpand(true).build(),
+            drawing_area: DrawingArea::builder()
+                .width_request(400)
+                .height_request(300)
+                .hexpand(true)
+                .vexpand(true)
+                .build(),
             drawing_context: create_drawing_context(),
             document_canvas: None,
         };
@@ -138,11 +155,93 @@ fn draw(ui: &Ui, area: &DrawingArea, context: &Context) {
         return;
     }
     let document_canvas = ui.document_canvas.as_ref().unwrap();
+    if document_canvas.num_pages > 1 {
+        draw_two_pages(ui, area, context);
+    } else {
+        draw_single_page(ui, area, context);
+    }
+}
+
+fn draw_two_pages(ui: &Ui, area: &DrawingArea, context: &Context) {
+    if ui.document_canvas.is_none() {
+        return;
+    }
+    let document_canvas = ui.document_canvas.as_ref().unwrap();
+
+    // Add white background
+    // context.set_source_rgba(1.0, 1.0, 1.0, 1.0);
+    // context.fill().unwrap();
+    // context.paint().unwrap();
+
+    let page_left = document_canvas
+        .document
+        .page(document_canvas.current_page_number - 1)
+        .unwrap();
+    let page_right = document_canvas
+        .document
+        .page(document_canvas.current_page_number)
+        .unwrap();
+
+    let (w_left, h_left) = page_left.size();
+    let (w_right, h_right) = page_right.size();
+
+    let h_max = f64::max(h_left, h_right);
+    // Make sure both pages are rendered with the same height
+    let w_max = match h_left < h_right {
+        true => w_left * h_right / h_left + w_right,
+        false => w_left + w_right * h_left / h_right,
+    };
+
+    let h_scale = area.height() as f64 / h_max;
+    let w_scale = area.width() as f64 / w_max;
+    let scale = f64::min(h_scale, w_scale);
+    let h_page = h_max * scale;
+
+    let scale_left = h_page / h_left;
+    let scale_right = h_page / h_right;
 
     context.set_source_rgba(1.0, 1.0, 1.0, 1.0);
-    context.paint().unwrap();
-    context.fill().expect("uh oh");
-    context.paint().unwrap();
+    context.save().unwrap();
+    context.translate(
+        area.width() as f64 / 2.0 - w_left * scale_left,
+        area.height() as f64 / 2.0 - h_page / 2.0,
+    );
+    // Poppler sometimes crops white border, draw it manually
+    context.rectangle(0.0, 0.0, w_left * scale_left, h_page);
+    context.fill().unwrap();
+    context.scale(scale_left, scale_left);
+    page_left.render(context);
+
+    context.restore().unwrap();
+    context.translate(
+        area.width() as f64 / 2.0,
+        area.height() as f64 / 2.0 - h_page / 2.0,
+    );
+    // Poppler sometimes crops white border, draw it manually
+    context.rectangle(0.0, 0.0, w_right * scale_right, h_page);
+    context.fill().unwrap();
+    context.scale(scale_right, scale_right);
+    page_right.render(context);
+
+    let r = ui.drawing_context.paint();
+    match r {
+        Err(v) => println!("Error painting PDF: {v:?}"),
+        Ok(_v) => {}
+    }
+
+    ui.drawing_context.show_page().unwrap();
+}
+fn draw_single_page(ui: &Ui, area: &DrawingArea, context: &Context) {
+    if ui.document_canvas.is_none() {
+        return;
+    }
+    let document_canvas = ui.document_canvas.as_ref().unwrap();
+
+    // Draw background
+    // context.set_source_rgba(1.0, 1.0, 1.0, 1.0);
+    // context.paint().unwrap();
+    // context.fill().expect("uh oh");
+    // context.paint().unwrap();
 
     let page = document_canvas
         .document
@@ -152,7 +251,6 @@ fn draw(ui: &Ui, area: &DrawingArea, context: &Context) {
 
     let width_diff = area.width() as f64 / w;
     let height_diff = area.height() as f64 / h;
-    context.save().unwrap();
     if width_diff > height_diff {
         context.translate(
             (area.width() as f64 - w * height_diff) / 2.0,
@@ -167,6 +265,11 @@ fn draw(ui: &Ui, area: &DrawingArea, context: &Context) {
         context.scale(width_diff, width_diff);
     }
 
+    // Poppler sometimes crops white border, draw it manually
+    context.set_source_rgba(1.0, 1.0, 1.0, 1.0);
+    context.rectangle(0.0, 0.0, w, h);
+    context.fill().unwrap();
+
     page.render(context);
 
     let r = ui.drawing_context.paint();