PDFViewer: Support a continuous page view mode

Author: https://github.com/mattco98
Commit: https://github.com/SerenityOS/serenity/commit/3ecb41b7d9
Pull-request: https://github.com/SerenityOS/serenity/pull/13394
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/nico

Userland/Applications/PDFViewer/PDFViewer.cpp

@@ -7,13 +7,14 @@
 
 #include "PDFViewer.h"
 #include <AK/Array.h>
+#include <AK/BinarySearch.h>
 #include <LibConfig/Client.h>
 #include <LibGUI/Action.h>
 #include <LibGUI/MessageBox.h>
 #include <LibGUI/Painter.h>
 #include <LibPDF/Renderer.h>
 
-static constexpr int PAGE_PADDING = 25;
+static constexpr int PAGE_PADDING = 10;
 
 static constexpr Array zoom_levels = {
     17,
@@ -46,7 +47,7 @@ PDFViewer::PDFViewer()
     m_page_view_mode = static_cast<PageViewMode>(Config::read_i32("PDFViewer", "Display", "PageMode", 0));
 }
 
-void PDFViewer::set_document(RefPtr<PDF::Document> document)
+PDF::PDFErrorOr<void> PDFViewer::set_document(RefPtr<PDF::Document> document)
 {
     m_document = document;
     m_current_page_index = document->get_first_page_index();
@@ -57,7 +58,10 @@ void PDFViewer::set_document(RefPtr<PDF::Document> document)
     for (u32 i = 0; i < document->get_page_count(); i++)
         m_rendered_page_list.unchecked_append(HashMap<u32, RenderedPage>());
 
+    TRY(cache_page_dimensions(true));
     update();
+
+    return {};
 }
 
 PDF::PDFErrorOr<NonnullRefPtr<Gfx::Bitmap>> PDFViewer::get_rendered_page(u32 index)
@@ -67,8 +71,7 @@ PDF::PDFErrorOr<NonnullRefPtr<Gfx::Bitmap>> PDFViewer::get_rendered_page(u32 ind
     if (existing_rendered_page.has_value() && existing_rendered_page.value().rotation == m_rotations)
         return existing_rendered_page.value().bitmap;
 
-    auto page = TRY(m_document->get_page(index));
-    auto rendered_page = TRY(render_page(page));
+    auto rendered_page = TRY(render_page(index));
     rendered_page_map.set(m_zoom_level, { rendered_page, m_rotations });
     return rendered_page;
 }
@@ -85,29 +88,79 @@ void PDFViewer::paint_event(GUI::PaintEvent& event)
     if (!m_document)
         return;
 
-    auto maybe_page = get_rendered_page(m_current_page_index);
-    if (maybe_page.is_error()) {
-        auto error = maybe_page.release_error();
-        GUI::MessageBox::show_error(nullptr, String::formatted("Error rendering page:\n{}", error.message()));
+    auto handle_error = [&]<typename T>(PDF::PDFErrorOr<T> maybe_error) {
+        if (maybe_error.is_error()) {
+            auto error = maybe_error.release_error();
+            GUI::MessageBox::show_error(nullptr, String::formatted("Error rendering page:\n{}", error.message()));
+            return true;
+        }
+        return false;
+    };
+
+    if (m_page_view_mode == PageViewMode::Single) {
+        auto maybe_page = get_rendered_page(m_current_page_index);
+        if (handle_error(maybe_page))
+            return;
+
+        auto page = maybe_page.release_value();
+        set_content_size(page->size());
+
+        painter.translate(frame_thickness(), frame_thickness());
+        painter.translate(-horizontal_scrollbar().value(), -vertical_scrollbar().value());
+
+        int x = max(0, (width() - page->width()) / 2);
+        int y = max(0, (height() - page->height()) / 2);
+
+        painter.blit({ x, y }, *page, page->rect());
         return;
     }
 
-    auto page = maybe_page.release_value();
-    set_content_size(page->size());
+    set_content_size({ m_page_dimension_cache.max_width, m_page_dimension_cache.total_height });
+
+    size_t first_page_index = 0;
+    size_t last_page_index = 0;
+
+    binary_search(m_page_dimension_cache.render_info, vertical_scrollbar().value(), &first_page_index, [](int height, PageDimensionCache::RenderInfo const& render_info) {
+        return height - render_info.total_height_before_this_page;
+    });
+
+    binary_search(m_page_dimension_cache.render_info, vertical_scrollbar().value() + height(), &last_page_index, [](int height, PageDimensionCache::RenderInfo const& render_info) {
+        return height - render_info.total_height_before_this_page;
+    });
+
+    auto initial_offset = m_page_dimension_cache.render_info[first_page_index].total_height_before_this_page - vertical_scrollbar().value();
 
     painter.translate(frame_thickness(), frame_thickness());
-    painter.translate(-horizontal_scrollbar().value(), -vertical_scrollbar().value());
+    painter.translate(-horizontal_scrollbar().value(), initial_offset);
+    auto middle = height() / 2;
+    auto y_offset = initial_offset;
 
-    int x = max(0, (width() - page->width()) / 2);
-    int y = max(0, (height() - page->height()) / 2);
+    for (size_t page_index = first_page_index; page_index <= last_page_index; page_index++) {
+        auto maybe_page = get_rendered_page(page_index);
+        if (handle_error(maybe_page))
+            return;
 
-    painter.blit({ x, y }, *page, page->rect());
+        auto page = maybe_page.release_value();
+
+        auto x = max(0, (width() - page->width()) / 2);
+
+        painter.blit({ x, PAGE_PADDING }, *page, page->rect());
+        auto diff_y = page->height() + PAGE_PADDING * 2;
+        painter.translate(0, diff_y);
+
+        if (y_offset < middle && y_offset + diff_y >= middle)
+            change_page(page_index);
+
+        y_offset += diff_y;
+    }
 }
 
 void PDFViewer::resize_event(GUI::ResizeEvent&)
 {
     for (auto& map : m_rendered_page_list)
         map.clear();
+    if (m_document)
+        MUST(cache_page_dimensions());
     update();
 }
 
@@ -124,15 +177,24 @@ void PDFViewer::mousewheel_event(GUI::MouseEvent& event)
         } else {
             zoom_in();
         }
-    } else {
-        auto& scrollbar = event.shift() ? horizontal_scrollbar() : vertical_scrollbar();
+        return;
+    }
 
+    auto& scrollbar = event.shift() ? horizontal_scrollbar() : vertical_scrollbar();
+
+    if (m_page_view_mode == PageViewMode::Multiple) {
+        if (scrolled_down) {
+            if (scrollbar.value() != scrollbar.max())
+                scrollbar.increase_slider_by(20);
+        } else {
+            if (scrollbar.value() > 0)
+                scrollbar.decrease_slider_by(20);
+        }
+    } else {
         if (scrolled_down) {
             if (scrollbar.value() == scrollbar.max()) {
-                if (m_current_page_index < m_document->get_page_count() - 1 && !event.shift()) {
-                    m_current_page_index++;
-                    if (on_page_change)
-                        on_page_change(m_current_page_index);
+                if (m_current_page_index < m_document->get_page_count() - 1) {
+                    change_page(m_current_page_index + 1);
                     scrollbar.set_value(0);
                 }
             } else {
@@ -140,18 +202,17 @@ void PDFViewer::mousewheel_event(GUI::MouseEvent& event)
             }
         } else {
             if (scrollbar.value() == 0) {
-                if (m_current_page_index > 0 && !event.shift()) {
-                    m_current_page_index--;
-                    if (on_page_change)
-                        on_page_change(m_current_page_index);
+                if (m_current_page_index > 0) {
+                    change_page(m_current_page_index - 1);
                     scrollbar.set_value(scrollbar.max());
                 }
             } else {
                 scrollbar.decrease_slider_by(20);
             }
         }
-        update();
     }
+
+    update();
 }
 
 void PDFViewer::mousedown_event(GUI::MouseEvent& event)
@@ -190,6 +251,7 @@ void PDFViewer::zoom_in()
 {
     if (m_zoom_level < zoom_levels.size() - 1) {
         m_zoom_level++;
+        MUST(cache_page_dimensions());
         update();
     }
 }
@@ -198,6 +260,7 @@ void PDFViewer::zoom_out()
 {
     if (m_zoom_level > 0) {
         m_zoom_level--;
+        MUST(cache_page_dimensions());
         update();
     }
 }
@@ -205,12 +268,14 @@ void PDFViewer::zoom_out()
 void PDFViewer::reset_zoom()
 {
     m_zoom_level = initial_zoom_level;
+    MUST(cache_page_dimensions());
     update();
 }
 
 void PDFViewer::rotate(int degrees)
 {
     m_rotations = (m_rotations + degrees + 360) % 360;
+    MUST(cache_page_dimensions());
     update();
 }
 
@@ -221,17 +286,11 @@ void PDFViewer::set_page_view_mode(PageViewMode mode)
     update();
 }
 
-PDF::PDFErrorOr<NonnullRefPtr<Gfx::Bitmap>> PDFViewer::render_page(const PDF::Page& page)
+PDF::PDFErrorOr<NonnullRefPtr<Gfx::Bitmap>> PDFViewer::render_page(u32 page_index)
 {
-    auto zoom_scale_factor = static_cast<float>(zoom_levels[m_zoom_level]) / 100.0f;
-
-    auto page_width = page.media_box.upper_right_x - page.media_box.lower_left_x;
-    auto page_height = page.media_box.upper_right_y - page.media_box.lower_left_y;
-    auto page_scale_factor = page_height / page_width;
-
-    auto height = static_cast<float>(this->height() - 2 * frame_thickness() - PAGE_PADDING * 2) * zoom_scale_factor;
-    auto width = height / page_scale_factor;
-    auto bitmap = Gfx::Bitmap::try_create(Gfx::BitmapFormat::BGRA8888, { width, height }).release_value_but_fixme_should_propagate_errors();
+    auto page = TRY(m_document->get_page(page_index));
+    auto& page_size = m_page_dimension_cache.render_info[page_index].size;
+    auto bitmap = Gfx::Bitmap::try_create(Gfx::BitmapFormat::BGRA8888, page_size.to_type<int>()).release_value_but_fixme_should_propagate_errors();
 
     TRY(PDF::Renderer::render(*m_document, page, bitmap));
 
@@ -247,3 +306,61 @@ PDF::PDFErrorOr<NonnullRefPtr<Gfx::Bitmap>> PDFViewer::render_page(const PDF::Pa
 
     return bitmap;
 }
+
+PDF::PDFErrorOr<void> PDFViewer::cache_page_dimensions(bool recalculate_fixed_info)
+{
+    if (recalculate_fixed_info)
+        m_page_dimension_cache.page_info.clear_with_capacity();
+
+    if (m_page_dimension_cache.page_info.is_empty()) {
+        m_page_dimension_cache.page_info.ensure_capacity(m_document->get_page_count());
+        for (size_t i = 0; i < m_document->get_page_count(); i++) {
+            auto page = TRY(m_document->get_page(i));
+            auto box = page.media_box;
+            m_page_dimension_cache.page_info.unchecked_append(PageDimensionCache::PageInfo {
+                { box.width(), box.height() },
+                page.rotate,
+            });
+        }
+    }
+
+    auto zoom_scale_factor = static_cast<float>(zoom_levels[m_zoom_level]) / 100.0f;
+
+    m_page_dimension_cache.render_info.clear_with_capacity();
+    m_page_dimension_cache.render_info.ensure_capacity(m_page_dimension_cache.page_info.size());
+
+    float max_width = 0;
+    float total_height = 0;
+
+    for (size_t i = 0; i < m_page_dimension_cache.page_info.size(); i++) {
+        auto& [size, rotation] = m_page_dimension_cache.page_info[i];
+        rotation += m_rotations;
+        auto page_scale_factor = size.height() / size.width();
+
+        auto height = static_cast<float>(this->height() - 2 * frame_thickness()) * zoom_scale_factor - PAGE_PADDING * 2;
+        auto width = height / page_scale_factor;
+        if (rotation % 2)
+            swap(width, height);
+
+        max_width = max(max_width, width);
+
+        m_page_dimension_cache.render_info.append({
+            { width, height },
+            total_height,
+        });
+
+        total_height += height;
+    }
+
+    m_page_dimension_cache.max_width = max_width;
+    m_page_dimension_cache.total_height = total_height;
+
+    return {};
+}
+
+void PDFViewer::change_page(u32 new_page)
+{
+    m_current_page_index = new_page;
+    if (on_page_change)
+        on_page_change(m_current_page_index);
+}

Userland/Applications/PDFViewer/PDFViewer.h

@@ -14,6 +14,26 @@
 
 static constexpr size_t initial_zoom_level = 8;
 
+struct PageDimensionCache {
+    // Fixed for a given document
+    struct PageInfo {
+        Gfx::FloatSize size;
+        int rotation;
+    };
+
+    // Based on PageInfo, also depends on some dynamic factors like
+    // zoom level and app size
+    struct RenderInfo {
+        Gfx::FloatSize size;
+        float total_height_before_this_page;
+    };
+
+    Vector<PageInfo> page_info;
+    Vector<RenderInfo> render_info;
+    float max_width;
+    float total_height;
+};
+
 class PDFViewer : public GUI::AbstractScrollableWidget {
     C_OBJECT(PDFViewer)
 
@@ -29,7 +49,7 @@ public:
     ALWAYS_INLINE void set_current_page(u32 current_page) { m_current_page_index = current_page; }
 
     ALWAYS_INLINE RefPtr<PDF::Document> const& document() const { return m_document; }
-    void set_document(RefPtr<PDF::Document>);
+    PDF::PDFErrorOr<void> set_document(RefPtr<PDF::Document>);
 
     Function<void(u32 new_page)> on_page_change;
 
@@ -59,13 +79,16 @@ private:
     };
 
     PDF::PDFErrorOr<NonnullRefPtr<Gfx::Bitmap>> get_rendered_page(u32 index);
-    PDF::PDFErrorOr<NonnullRefPtr<Gfx::Bitmap>> render_page(const PDF::Page&);
+    PDF::PDFErrorOr<NonnullRefPtr<Gfx::Bitmap>> render_page(u32 page_index);
+    PDF::PDFErrorOr<void> cache_page_dimensions(bool recalculate_fixed_info = false);
+    void change_page(u32 new_page);
 
     RefPtr<PDF::Document> m_document;
     u32 m_current_page_index { 0 };
     Vector<HashMap<u32, RenderedPage>> m_rendered_page_list;
 
     u8 m_zoom_level { initial_zoom_level };
+    PageDimensionCache m_page_dimension_cache;
     PageViewMode m_page_view_mode;
 
     Gfx::IntPoint m_pan_starting_position;

Userland/Applications/PDFViewer/PDFViewerWidget.cpp

@@ -171,13 +171,19 @@ void PDFViewerWidget::open_file(Core::File& file)
 {
     window()->set_title(String::formatted("{} - PDF Viewer", file.filename()));
 
+    auto handle_error = [&]<typename T>(PDF::PDFErrorOr<T> maybe_error) {
+        if (maybe_error.is_error()) {
+            auto error = maybe_error.release_error();
+            GUI::MessageBox::show_error(nullptr, String::formatted("Couldn't load PDF {}:\n{}", file.filename(), error.message()));
+            return true;
+        }
+        return false;
+    };
+
     m_buffer = file.read_all();
     auto maybe_document = PDF::Document::create(m_buffer);
-    if (maybe_document.is_error()) {
-        auto error = maybe_document.release_error();
-        GUI::MessageBox::show_error(nullptr, String::formatted("Couldn't load PDF {}:\n{}", file.filename(), error.message()));
+    if (handle_error(maybe_document))
         return;
-    }
 
     auto document = maybe_document.release_value();
 
@@ -186,14 +192,12 @@ void PDFViewerWidget::open_file(Core::File& file)
         VERIFY_NOT_REACHED();
     }
 
-    auto result = document->initialize();
-    if (result.is_error()) {
-        auto error = result.release_error();
-        GUI::MessageBox::show_error(nullptr, String::formatted("Couldn't load PDF {}:\n{}", file.filename(), error.message()));
+    if (handle_error(document->initialize()))
+        return;
+
+    if (handle_error(m_viewer->set_document(document)))
         return;
-    }
 
-    m_viewer->set_document(document);
     m_total_page_label->set_text(String::formatted("of {}", document->get_page_count()));
 
     m_page_text_box->set_enabled(true);

Userland/Libraries/LibPDF/Document.h

@@ -23,6 +23,9 @@ struct Rectangle {
     float lower_left_y;
     float upper_right_x;
     float upper_right_y;
+
+    float width() const { return upper_right_x - lower_left_x; }
+    float height() const { return upper_right_y - lower_left_y; }
 };
 
 struct Page {

Userland/Libraries/LibPDF/Renderer.cpp

@@ -38,8 +38,8 @@ Renderer::Renderer(RefPtr<Document> document, Page const& page, RefPtr<Gfx::Bitm
     Gfx::AffineTransform userspace_matrix;
     userspace_matrix.translate(media_box.lower_left_x, media_box.lower_left_y);
 
-    float width = media_box.upper_right_x - media_box.lower_left_x;
-    float height = media_box.upper_right_y - media_box.lower_left_y;
+    float width = media_box.width();
+    float height = media_box.height();
     float scale_x = static_cast<float>(bitmap->width()) / width;
     float scale_y = static_cast<float>(bitmap->height()) / height;
     userspace_matrix.scale(scale_x, scale_y);