[PDF Ink Signatures] Add brush invalidation area method

Points collected while doing stroking with a brush will not be visible
to the user unless the viewport is properly notified to repaint the
affected areas.

Introduce a PdfInkBrush method to help determine the minimal area to be
invalidated based on the size of the brush.

Bug: 335517471
Change-Id: Ie0b787d6fc8b5a028d1e39b42749cdf02e173738
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5634395
Commit-Queue: Alan Screen <awscreen@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1316610}

pdf/BUILD.gn

@@ -457,6 +457,7 @@ if (enable_pdf) {
     if (enable_pdf_ink2) {
       sources += [
         "ink_module_unittest.cc",
+        "pdf_ink_brush_unittest.cc",
         "pdf_ink_transform_unittest.cc",
         "pdf_ink_undo_redo_model_unittest.cc",
       ]

pdf/pdf_ink_brush.cc

@@ -13,6 +13,8 @@
 #include "pdf/ink/ink_brush_family.h"
 #include "pdf/ink/ink_brush_paint.h"
 #include "pdf/ink/ink_brush_tip.h"
+#include "ui/gfx/geometry/point_f.h"
+#include "ui/gfx/geometry/rect_conversions.h"
 
 namespace chrome_pdf {
 
@@ -64,6 +66,17 @@ std::unique_ptr<InkBrush> CreateInkBrush(PdfInkBrush::Type type,
                           /*epsilon=*/0.1f);
 }
 
+// Determine the area to invalidate centered around a point where a brush is
+// applied.
+gfx::Rect GetPointInvalidateArea(float brush_diameter,
+                                 const gfx::PointF& center) {
+  // Choose a rectangle that surrounds the point for the brush radius.
+  float brush_radius = brush_diameter / 2;
+  return gfx::ToEnclosingRect(gfx::RectF(center.x() - brush_radius,
+                                         center.y() - brush_radius,
+                                         brush_diameter, brush_diameter));
+}
+
 }  // namespace
 
 // static
@@ -89,4 +102,17 @@ const InkBrush& PdfInkBrush::GetInkBrush() const {
   return *ink_brush_;
 }
 
+// Determine the area to invalidate encompassing a line between two
+// consecutive points where a brush is applied.
+gfx::Rect PdfInkBrush::GetInvalidateArea(const gfx::PointF& center1,
+                                         const gfx::PointF& center2) const {
+  // For a line connecting `center1` to `center2`, the invalidate
+  // region is the union between the areas affected by them both.
+  float brush_diameter = ink_brush_->GetSize();
+  gfx::Rect area1 = GetPointInvalidateArea(brush_diameter, center1);
+  gfx::Rect area2 = GetPointInvalidateArea(brush_diameter, center2);
+  area2.Union(area1);
+  return area2;
+}
+
 }  // namespace chrome_pdf

pdf/pdf_ink_brush.h

@@ -10,13 +10,18 @@
 #include <string>
 
 #include "third_party/skia/include/core/SkColor.h"
+#include "ui/gfx/geometry/rect.h"
+
+namespace gfx {
+class PointF;
+}
 
 namespace chrome_pdf {
 
 class InkBrush;
 
-// A wrapper class used to create ink brushes specifically for PDF annotation
-// mode.
+// A class used to create ink brushes for PDF annotation mode and support
+// invalidation for rendering.
 class PdfInkBrush {
  public:
   // The types of brushes supported in PDF annotation mode.
@@ -37,6 +42,13 @@ class PdfInkBrush {
   PdfInkBrush& operator=(const PdfInkBrush&) = delete;
   ~PdfInkBrush();
 
+  // Determine the area to invalidate encompassing a line between two
+  // consecutive points where a brush is applied.  Values are in screen-based
+  // coordinates.  The area to invalidated is correlated to the size of the
+  // brush.
+  gfx::Rect GetInvalidateArea(const gfx::PointF& center1,
+                              const gfx::PointF& center2) const;
+
   // Converts `brush_type` to a `Type`, returning `std::nullopt` if `brush_type`
   // does not correspond to any `Type`.
   static std::optional<Type> StringToType(const std::string& brush_type);

pdf/pdf_ink_brush_unittest.cc

@@ -0,0 +1,48 @@
+// Copyright 2024 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "pdf/pdf_ink_brush.h"
+
+#include <memory>
+
+#include "testing/gtest/include/gtest/gtest.h"
+#include "ui/gfx/geometry/point_f.h"
+#include "ui/gfx/geometry/rect.h"
+
+namespace chrome_pdf {
+
+namespace {
+
+std::unique_ptr<chrome_pdf::PdfInkBrush> CreatePdfInkBrush(float size) {
+  return std::make_unique<chrome_pdf::PdfInkBrush>(
+      chrome_pdf::PdfInkBrush::Type::kPen,
+      chrome_pdf::PdfInkBrush::Params{SK_ColorBLACK, size});
+}
+
+}  // namespace
+
+TEST(PdfInkBrushTest, InvalidateSinglePoint) {
+  constexpr gfx::PointF kPoint(40.0f, 16.0f);
+  auto brush = CreatePdfInkBrush(/*size=*/10.0f);
+  EXPECT_EQ(gfx::Rect(35, 11, 10, 10),
+            brush->GetInvalidateArea(kPoint, kPoint));
+}
+
+TEST(PdfInkBrushTest, InvalidateSinglePointNearBorder) {
+  // Using a point closer to the border than the radius of the brush results in
+  // the invalidation area including a negative origin.
+  constexpr gfx::PointF kPoint(3.0f, 4.0f);
+  auto brush = CreatePdfInkBrush(/*size=*/13.0f);
+  EXPECT_EQ(gfx::Rect(-4, -3, 14, 14),
+            brush->GetInvalidateArea(kPoint, kPoint));
+}
+
+TEST(PdfInkBrushTest, InvalidateDifferentPoints) {
+  auto brush = CreatePdfInkBrush(/*size=*/10.0f);
+  EXPECT_EQ(gfx::Rect(10, 11, 35, 26),
+            brush->GetInvalidateArea(gfx::PointF(40.0f, 16.0f),
+                                     gfx::PointF(15.0f, 32.0f)));
+}
+
+}  // namespace chrome_pdf