Add viewport scroll information to PDFAccessibilityTree

This CL adds following information to PDFAccessibilityTree
- ax::mojom::IntAttribute::kScrollXMin
- ax::mojom::IntAttribute::kScrollXMax
- ax::mojom::IntAttribute::kScrollX
- ax::mojom::IntAttribute::kScrollYMin
- ax::mojom::IntAttribute::kScrollYMax
- ax::mojom::IntAttribute::kScrollY

It enables partial implementation of IScrollProvider, following methods
will work with this change
- IScrollProvider::get_HorizontallyScrollable
- IScrollProvider::get_VerticallyScrollable
- IScrollProvider::get_HorizontalScrollPercent
- IScrollProvider::get_VerticalScrollPercent

This information is required by Screen readers to announce the current
scroll position and extent of scroll to the user.

Tests: The best way to test this change will be through browser tests.
However, it requires the second part of the change, detailed in the
associated bug, to be completed.

Bug: 1034521
Change-Id: I11067b2af4d5bd73e62d89c8ce86fb00b5f3f7ec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1969412Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Kevin Babbitt <kbabbitt@microsoft.com>
Commit-Queue: Virender Singh <virens@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#727858}

components/pdf/renderer/pdf_accessibility_tree.cc

@@ -362,6 +362,16 @@ void PdfAccessibilityTree::SetAccessibilityViewportInfo(
   if (render_accessibility && tree_.size() > 1) {
     ui::AXNode* root = tree_.root();
     ui::AXNodeData root_data = root->data();
+    root_data.AddIntAttribute(ax::mojom::IntAttribute::kScrollXMin, 0);
+    root_data.AddIntAttribute(ax::mojom::IntAttribute::kScrollXMax,
+                              viewport_info.total_scrollable_size.width);
+    root_data.AddIntAttribute(ax::mojom::IntAttribute::kScrollX,
+                              viewport_info.current_scroll_position.x);
+    root_data.AddIntAttribute(ax::mojom::IntAttribute::kScrollYMin, 0);
+    root_data.AddIntAttribute(ax::mojom::IntAttribute::kScrollYMax,
+                              viewport_info.total_scrollable_size.height);
+    root_data.AddIntAttribute(ax::mojom::IntAttribute::kScrollY,
+                              viewport_info.current_scroll_position.y);
     root_data.relative_bounds.transform =
         base::WrapUnique(MakeTransformFromViewInfo());
     root->SetData(root_data);

pdf/out_of_process_instance.cc

@@ -1009,6 +1009,10 @@ void OutOfProcessInstance::SendAccessibilityViewportInfo() {
 
   viewport_info.zoom = zoom_;
   viewport_info.scale = device_scale_;
+  viewport_info.total_scrollable_size = {GetTotalScrollableWidth(),
+                                         GetTotalScrollableHeight()};
+  viewport_info.current_scroll_position = {GetHorizontalScrollPosition(),
+                                           GetVerticalScrollPosition()};
 
   engine_->GetSelection(&viewport_info.selection_start_page_index,
                         &viewport_info.selection_start_char_index,
@@ -1291,6 +1295,25 @@ int OutOfProcessInstance::GetDocumentPixelHeight() const {
       ceil(document_size_.height() * zoom_ * device_scale_));
 }
 
+int OutOfProcessInstance::GetTotalScrollableWidth() const {
+  return std::max(GetDocumentPixelWidth() - plugin_size_.width(), 0);
+}
+
+int OutOfProcessInstance::GetTotalScrollableHeight() const {
+  return std::max(static_cast<int>(GetDocumentPixelHeight() +
+                                   GetToolbarHeightInScreenCoords() -
+                                   plugin_size_.height()),
+                  0);
+}
+
+int OutOfProcessInstance::GetHorizontalScrollPosition() const {
+  return static_cast<int>(scroll_offset_.x() * device_scale_);
+}
+
+int OutOfProcessInstance::GetVerticalScrollPosition() const {
+  return static_cast<int>(scroll_offset_.y() * device_scale_);
+}
+
 void OutOfProcessInstance::FillRect(const pp::Rect& rect, uint32_t color) {
   DCHECK(!image_data_.is_null() || rect.IsEmpty());
   uint32_t* buffer_start = static_cast<uint32_t*>(image_data_.data());
@@ -1982,7 +2005,7 @@ void OutOfProcessInstance::IsEditModeChanged(bool is_edit_mode) {
   pp::PDF::SetPluginCanSave(this, ShouldSaveEdits());
 }
 
-float OutOfProcessInstance::GetToolbarHeightInScreenCoords() {
+float OutOfProcessInstance::GetToolbarHeightInScreenCoords() const {
   return top_toolbar_height_in_viewport_coords_ * device_scale_;
 }
 

pdf/out_of_process_instance.h

@@ -149,7 +149,7 @@ class OutOfProcessInstance : public pp::Instance,
   void IsSelectingChanged(bool is_selecting) override;
   void SelectionChanged(const pp::Rect& left, const pp::Rect& right) override;
   void IsEditModeChanged(bool is_edit_mode) override;
-  float GetToolbarHeightInScreenCoords() override;
+  float GetToolbarHeightInScreenCoords() const override;
 
   // PreviewModeClient::Client implementation.
   void PreviewDocumentLoadComplete() override;
@@ -179,6 +179,14 @@ class OutOfProcessInstance : public pp::Instance,
   int GetDocumentPixelWidth() const;
   int GetDocumentPixelHeight() const;
 
+  // Computes total scrollable Width and Height of the document.
+  int GetTotalScrollableWidth() const;
+  int GetTotalScrollableHeight() const;
+
+  // Computes current horizontal and scroll position of the document.
+  int GetHorizontalScrollPosition() const;
+  int GetVerticalScrollPosition() const;
+
   // Draws a rectangle with the specified dimensions and color in our buffer.
   void FillRect(const pp::Rect& rect, uint32_t color);
 

pdf/pdf_engine.h

@@ -281,7 +281,7 @@ class PDFEngine {
 
     // Gets the height of the top toolbar in screen coordinates. This is
     // independent of whether it is hidden or not at the moment.
-    virtual float GetToolbarHeightInScreenCoords() = 0;
+    virtual float GetToolbarHeightInScreenCoords() const = 0;
   };
 
   struct AccessibilityLinkInfo {

pdf/preview_mode_client.cc

@@ -150,7 +150,7 @@ bool PreviewModeClient::IsPrintPreview() {
   return false;
 }
 
-float PreviewModeClient::GetToolbarHeightInScreenCoords() {
+float PreviewModeClient::GetToolbarHeightInScreenCoords() const {
   return 0.0f;
 }
 

pdf/preview_mode_client.h

@@ -67,7 +67,7 @@ class PreviewModeClient : public PDFEngine::Client {
   void DocumentHasUnsupportedFeature(const std::string& feature) override;
   void FormTextFieldFocusChange(bool in_focus) override;
   bool IsPrintPreview() override;
-  float GetToolbarHeightInScreenCoords() override;
+  float GetToolbarHeightInScreenCoords() const override;
   uint32_t GetBackgroundColor() override;
 
  private:

pdf/test/test_client.cc

@@ -56,7 +56,7 @@ uint32_t TestClient::GetBackgroundColor() {
   return 0;
 }
 
-float TestClient::GetToolbarHeightInScreenCoords() {
+float TestClient::GetToolbarHeightInScreenCoords() const {
   return 0;
 }
 

pdf/test/test_client.h

@@ -37,7 +37,7 @@ class TestClient : public PDFEngine::Client {
   pp::Instance* GetPluginInstance() override;
   bool IsPrintPreview() override;
   uint32_t GetBackgroundColor() override;
-  float GetToolbarHeightInScreenCoords() override;
+  float GetToolbarHeightInScreenCoords() const override;
 
  private:
   // Not owned. Expected to dangle briefly, as the engine usually is destroyed

ppapi/c/private/ppb_pdf.h

@@ -36,6 +36,10 @@ struct PP_PrivateFindResult {
 struct PP_PrivateAccessibilityViewportInfo {
   double zoom;
   double scale;
+  // |total_scrollable_size| and |current_scroll_position| are relative
+  // to plugin embed and in screen coordinates.
+  struct PP_Size total_scrollable_size;
+  struct PP_Point current_scroll_position;
   struct PP_Point scroll;
   struct PP_Point offset;
   uint32_t selection_start_page_index;

ppapi/proxy/ppapi_messages.h

@@ -268,6 +268,8 @@ IPC_STRUCT_TRAITS_END()
 IPC_STRUCT_TRAITS_BEGIN(PP_PrivateAccessibilityViewportInfo)
   IPC_STRUCT_TRAITS_MEMBER(zoom)
   IPC_STRUCT_TRAITS_MEMBER(scale)
+  IPC_STRUCT_TRAITS_MEMBER(total_scrollable_size)
+  IPC_STRUCT_TRAITS_MEMBER(current_scroll_position)
   IPC_STRUCT_TRAITS_MEMBER(scroll)
   IPC_STRUCT_TRAITS_MEMBER(offset)
   IPC_STRUCT_TRAITS_MEMBER(selection_start_page_index)