LibPDF+PDFViewer+MacPDF: Don't draw hidden text by default

Text can be rendered in various ways in PDFs: Filled, stroked,
both filled and stroked, set as clipping path, hidden, or
some combinations thereof.

We don't implement any of this at the moment except "filled".

Hidden text is used in scanned documents: The image of the scan is
drawn in the background, and then OCRd text is "drawn" as hidden
on top of the scanned bitmap. That way, the (hidden) text can be
selected and copied, and it looks like you're selecting text from
the scanned bitmap. Find-in-page also works similarly. (We currently
have neither text selection nor find-in-page, but one day we will.)

Now that we have pretty good support for CCITT and are growing some
support for JBIG2, we now draw both the scanned background image
as well as the foreground text. They're not always perfectly aligned.

This change makes it so that we don't render text that's marked as
hidden. (We still do most of the coordinate math, which will probably
come in handy at some point when we implement text selection.)

This makes these scanned documents appear as they're supposed to
appear (at least in documents where we manage to decode the background
bitmap).

This also adds a debug option to force rendering of hidden text.

Meta/Lagom/Contrib/MacPDF/MacPDFView.h

@@ -31,5 +31,6 @@
 - (IBAction)toggleClipPaths:(id)sender;
 - (IBAction)toggleClipText:(id)sender;
 - (IBAction)toggleShowImages:(id)sender;
+- (IBAction)toggleShowHiddenText:(id)sender;
 
 @end

Meta/Lagom/Contrib/MacPDF/MacPDFView.mm

@@ -185,6 +185,10 @@ static NSBitmapImageRep* ns_from_gfx(NonnullRefPtr<Gfx::Bitmap> bitmap_p)
         [item setState:_preferences.show_images ? NSControlStateValueOn : NSControlStateValueOff];
         return _doc ? YES : NO;
     }
+    if ([item action] == @selector(toggleShowHiddenText:)) {
+        [item setState:_preferences.show_hidden_text ? NSControlStateValueOn : NSControlStateValueOff];
+        return _doc ? YES : NO;
+    }
     return NO;
 }
 
@@ -228,6 +232,14 @@ static NSBitmapImageRep* ns_from_gfx(NonnullRefPtr<Gfx::Bitmap> bitmap_p)
     }
 }
 
+- (IBAction)toggleShowHiddenText:(id)sender
+{
+    if (_doc) {
+        _preferences.show_hidden_text = !_preferences.show_hidden_text;
+        [self invalidateCachedBitmap];
+    }
+}
+
 - (void)keyDown:(NSEvent*)event
 {
     // Calls moveLeft: or moveRight: below.

Meta/Lagom/Contrib/MacPDF/MacPDFWindowController.h

@@ -26,6 +26,7 @@ NS_ASSUME_NONNULL_BEGIN
 - (IBAction)toggleClipPaths:(id)sender;
 - (IBAction)toggleClipText:(id)sender;
 - (IBAction)toggleShowImages:(id)sender;
+- (IBAction)toggleShowHiddenText:(id)sender;
 - (IBAction)showGoToPageDialog:(id)sender;
 
 - (void)pdfDidInitialize;

Meta/Lagom/Contrib/MacPDF/MacPDFWindowController.mm

@@ -164,6 +164,11 @@
     [_pdfView toggleShowImages:sender];
 }
 
+- (IBAction)toggleShowHiddenText:(id)sender
+{
+    [_pdfView toggleShowHiddenText:sender];
+}
+
 - (IBAction)showGoToPageDialog:(id)sender
 {
     auto alert = [[NSAlert alloc] init];

Meta/Lagom/Contrib/MacPDF/MainMenu.xib

@@ -694,6 +694,12 @@
                                     <action selector="toggleShowImages:" target="-1" id="mNE-9J-Nle"/>
                                 </connections>
                             </menuItem>
+                            <menuItem title="Show Hidden Text" id="PhM-XC-ExK">
+                                <modifierMask key="keyEquivalentModifierMask"/>
+                                <connections>
+                                    <action selector="toggleShowHiddenText:" target="-1" id="7iT-L2-Jd1"/>
+                                </connections>
+                            </menuItem>
                         </items>
                     </menu>
                 </menuItem>

Userland/Applications/PDFViewer/PDFViewer.cpp

@@ -48,6 +48,7 @@ PDFViewer::PDFViewer()
     m_page_view_mode = static_cast<PageViewMode>(Config::read_i32("PDFViewer"sv, "Display"sv, "PageMode"sv, 0));
     m_rendering_preferences.show_clipping_paths = Config::read_bool("PDFViewer"sv, "Rendering"sv, "ShowClippingPaths"sv, false);
     m_rendering_preferences.show_images = Config::read_bool("PDFViewer"sv, "Rendering"sv, "ShowImages"sv, true);
+    m_rendering_preferences.show_hidden_text = Config::read_bool("PDFViewer"sv, "Rendering"sv, "ShowHiddenText"sv, false);
     m_rendering_preferences.show_diagnostics = Config::read_bool("PDFViewer"sv, "Rendering"sv, "ShowDiagnostics"sv, false);
     m_rendering_preferences.clip_images = Config::read_bool("PDFViewer"sv, "Rendering"sv, "ClipImages"sv, true);
     m_rendering_preferences.clip_paths = Config::read_bool("PDFViewer"sv, "Rendering"sv, "ClipPaths"sv, true);
@@ -192,6 +193,13 @@ void PDFViewer::set_show_images(bool show_images)
     update();
 }
 
+void PDFViewer::set_show_hidden_text(bool show_hidden_text)
+{
+    m_rendering_preferences.show_hidden_text = show_hidden_text;
+    Config::write_bool("PDFViewer"sv, "Rendering"sv, "ShowHiddenText"sv, show_hidden_text);
+    update();
+}
+
 void PDFViewer::set_clip_images(bool clip_images)
 {
     m_rendering_preferences.clip_images = clip_images;

Userland/Applications/PDFViewer/PDFViewer.h

@@ -68,6 +68,8 @@ public:
     void set_show_clipping_paths(bool);
     bool show_images() const { return m_rendering_preferences.show_images; }
     void set_show_images(bool);
+    bool show_hidden_text() const { return m_rendering_preferences.show_hidden_text; }
+    void set_show_hidden_text(bool);
     bool clip_images() const { return m_rendering_preferences.clip_images; }
     void set_clip_images(bool);
     bool clip_paths() const { return m_rendering_preferences.clip_paths; }

Userland/Applications/PDFViewer/PDFViewerWidget.cpp

@@ -271,6 +271,11 @@ ErrorOr<void> PDFViewerWidget::initialize_menubar(GUI::Window& window)
     });
     toggle_show_images->set_checked(m_viewer->show_images());
     debug_menu->add_action(toggle_show_images);
+    auto toggle_show_hidden_text = GUI::Action::create_checkable("Show &Hidden Text", [&](auto& action) {
+        m_viewer->set_show_hidden_text(action.is_checked());
+    });
+    toggle_show_hidden_text->set_checked(m_viewer->show_hidden_text());
+    debug_menu->add_action(toggle_show_hidden_text);
     auto toggle_clip_images = GUI::Action::create_checkable("Clip I&mages", [&](auto& action) {
         m_viewer->set_clip_images(action.is_checked());
     });

Userland/Libraries/LibPDF/Fonts/SimpleFont.cpp

@@ -71,8 +71,10 @@ PDFErrorOr<Gfx::FloatPoint> SimpleFont::draw_string(Gfx::Painter& painter, Gfx::
         else
             glyph_width = font_size * m_missing_width * m_font_matrix.x_scale();
 
-        Gfx::FloatPoint glyph_render_position = text_rendering_matrix.map(glyph_position);
-        TRY(draw_glyph(painter, glyph_render_position, glyph_width, char_code, renderer));
+        if (renderer.text_state().rendering_mode != TextRenderingMode::Invisible || renderer.show_hidden_text()) {
+            Gfx::FloatPoint glyph_render_position = text_rendering_matrix.map(glyph_position);
+            TRY(draw_glyph(painter, glyph_render_position, glyph_width, char_code, renderer));
+        }
 
         // glyph_width is scaled by `text_rendering_matrix.x_scale() * renderer.text_state().font_size / horizontal_scaling`,
         // but it should only be scaled by `renderer.text_state().font_size`.

Userland/Libraries/LibPDF/Fonts/Type0Font.cpp

@@ -478,8 +478,10 @@ PDFErrorOr<Gfx::FloatPoint> Type0Font::draw_string(Gfx::Painter& painter, Gfx::F
             }
         }
 
-        Gfx::FloatPoint glyph_render_position = text_rendering_matrix.map(glyph_position - Gfx::FloatPoint { position_vector_x, position_vector_y });
-        TRY(m_cid_font_type->draw_glyph(painter, glyph_render_position, glyph_width, cid, renderer));
+        if (renderer.text_state().rendering_mode != TextRenderingMode::Invisible || renderer.show_hidden_text()) {
+            Gfx::FloatPoint glyph_render_position = text_rendering_matrix.map(glyph_position - Gfx::FloatPoint { position_vector_x, position_vector_y });
+            TRY(m_cid_font_type->draw_glyph(painter, glyph_render_position, glyph_width, cid, renderer));
+        }
 
         // glyph_width is scaled by `text_rendering_matrix.x_scale() * renderer.text_state().font_size / horizontal_scaling`,
         // but it should only be scaled by `renderer.text_state().font_size`.

Userland/Libraries/LibPDF/Renderer.h

@@ -89,6 +89,7 @@ struct GraphicsState {
 struct RenderingPreferences {
     bool show_clipping_paths { false };
     bool show_images { true };
+    bool show_hidden_text { false };
     bool show_diagnostics { false };
 
     bool clip_images { true };
@@ -121,6 +122,8 @@ public:
 
     PDFErrorOr<void> render_type3_glyph(Gfx::FloatPoint, StreamObject const&, Gfx::AffineTransform const&, Optional<NonnullRefPtr<DictObject>>);
 
+    bool show_hidden_text() const { return m_rendering_preferences.show_hidden_text; }
+
 private:
     Renderer(RefPtr<Document>, Page const&, RefPtr<Gfx::Bitmap>, Color background_color, RenderingPreferences);