[Impeller] libImpeller: Implement APIs for fetching glyph and line me…

…trics.

This patch adds support in the typography subsystem of the public
Impeller API such that users can implement text editing functionality.

* Line metrics for a fully laid out paragraph can be retrieved. The
  metrics contain information about offsets into the original code unit
  buffer used to create the paragraph. These offsets can be used to
  implement functionality that edits whole lines.
* Glyph information for a specific code unit offset, as well as a
  coordinate offset relative to the paragraph origin, can be obtained.
  This information can be used place decorations (like carets), select
  words surrounding the caret (a hit-test), and edit the source buffer
  to re-layout the paragraph.
* Word boundaries (as specified in Unicode Standard Annex 29) can be
  retrieved to select and modify paragraph subsets by character, word,
  and line at caret.

Like in Flutter, the code unit buffers are assumed to be arrays of
UTF-16 bytes. I'd have preferred this to be UTF-8 because the initial
paragraph construction is using UTF-8 bytes. Also, Skia internally seems
to work with UTF-8 too but the interfaces are exposed using UTF-16
(presumably for users like Flutter that work with Dart strings that are
UTF-16). Exposing additional APIs in txt::Paragraph to back this out
seemed onerous. Instead, a UTF-16 assumption for all APIs that retrieve
metrics is made (and documented). It stands to reason that paragraphs
should be constructable using UTF-16 buffers in the public API too. I'll
add that in a subsequent patch as that has little to do with metrics.

Fixes #165509

engine/src/flutter/impeller/toolkit/interop/BUILD.gn

@@ -41,8 +41,12 @@ impeller_component("interop_base") {
     "dl_builder.h",
     "formats.cc",
     "formats.h",
+    "glyph_info.cc",
+    "glyph_info.h",
     "image_filter.cc",
     "image_filter.h",
+    "line_metrics.cc",
+    "line_metrics.h",
     "mask_filter.cc",
     "mask_filter.h",
     "object.cc",

engine/src/flutter/impeller/toolkit/interop/glyph_info.cc

@@ -0,0 +1,42 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "impeller/toolkit/interop/glyph_info.h"
+
+namespace impeller::interop {
+
+GlyphInfo::~GlyphInfo() = default;
+
+size_t GlyphInfo::GetGraphemeClusterCodeUnitRangeBegin() const {
+  return info_.fGraphemeClusterTextRange.start;
+}
+
+size_t GlyphInfo::GetGraphemeClusterCodeUnitRangeEnd() const {
+  return info_.fGraphemeClusterTextRange.end;
+}
+
+ImpellerRect GlyphInfo::GetGraphemeClusterBounds() const {
+  return ImpellerRect{
+      info_.fGraphemeLayoutBounds.y(),
+      info_.fGraphemeLayoutBounds.x(),
+      info_.fGraphemeLayoutBounds.width(),
+      info_.fGraphemeLayoutBounds.height(),
+  };
+}
+
+bool GlyphInfo::IsEllipsis() const {
+  return info_.fIsEllipsis;
+}
+
+ImpellerTextDirection GlyphInfo::GetTextDirection() const {
+  switch (info_.fDirection) {
+    case skia::textlayout::TextDirection::kRtl:
+      return kImpellerTextDirectionRTL;
+    case skia::textlayout::TextDirection::kLtr:
+      return kImpellerTextDirectionLTR;
+  }
+  return kImpellerTextDirectionLTR;
+}
+
+}  // namespace impeller::interop

engine/src/flutter/impeller/toolkit/interop/glyph_info.h

@@ -0,0 +1,63 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef FLUTTER_IMPELLER_TOOLKIT_INTEROP_GLYPH_INFO_H_
+#define FLUTTER_IMPELLER_TOOLKIT_INTEROP_GLYPH_INFO_H_
+
+#include "flutter/third_party/skia/modules/skparagraph/include/Paragraph.h"
+#include "impeller/toolkit/interop/impeller.h"
+#include "impeller/toolkit/interop/object.h"
+
+namespace impeller::interop {
+
+//------------------------------------------------------------------------------
+/// @brief      Internal C++ peer of ImpellerGlyphInfo. For detailed
+///             documentation, refer to the headerdocs in the public API in
+///             impeller.h.
+///
+class GlyphInfo final
+    : public Object<GlyphInfo,
+                    IMPELLER_INTERNAL_HANDLE_NAME(ImpellerGlyphInfo)> {
+ public:
+  GlyphInfo(skia::textlayout::Paragraph::GlyphInfo info)
+      : info_(std::move(info)) {}
+
+  ~GlyphInfo();
+
+  GlyphInfo(const GlyphInfo&) = delete;
+
+  GlyphInfo& operator=(const GlyphInfo&) = delete;
+
+  //----------------------------------------------------------------------------
+  /// @see      ImpellerGlpyhInfoGetGraphemeClusterCodeUnitRangeBegin.
+  ///
+  size_t GetGraphemeClusterCodeUnitRangeBegin() const;
+
+  //----------------------------------------------------------------------------
+  /// @see      ImpellerGlpyhInfoGetGraphemeClusterCodeUnitRangeEnd.
+  ///
+  size_t GetGraphemeClusterCodeUnitRangeEnd() const;
+
+  //----------------------------------------------------------------------------
+  /// @see      ImpellerGlpyhInfoGetGraphemeClusterBounds.
+  ///
+  ImpellerRect GetGraphemeClusterBounds() const;
+
+  //----------------------------------------------------------------------------
+  /// @see      ImpellerGlyphInfoIsEllipsis.
+  ///
+  bool IsEllipsis() const;
+
+  //----------------------------------------------------------------------------
+  /// @see      ImpellerGlyphInfoGetTextDirection.
+  ///
+  ImpellerTextDirection GetTextDirection() const;
+
+ private:
+  const skia::textlayout::Paragraph::GlyphInfo info_;
+};
+
+}  // namespace impeller::interop
+
+#endif  // FLUTTER_IMPELLER_TOOLKIT_INTEROP_GLYPH_INFO_H_

engine/src/flutter/impeller/toolkit/interop/impeller.cc

@@ -17,7 +17,9 @@
 #include "impeller/toolkit/interop/context.h"
 #include "impeller/toolkit/interop/dl_builder.h"
 #include "impeller/toolkit/interop/formats.h"
+#include "impeller/toolkit/interop/glyph_info.h"
 #include "impeller/toolkit/interop/image_filter.h"
+#include "impeller/toolkit/interop/line_metrics.h"
 #include "impeller/toolkit/interop/mask_filter.h"
 #include "impeller/toolkit/interop/object.h"
 #include "impeller/toolkit/interop/paint.h"
@@ -58,7 +60,9 @@ DEFINE_PEER_GETTER(ColorSource, ImpellerColorSource);
 DEFINE_PEER_GETTER(Context, ImpellerContext);
 DEFINE_PEER_GETTER(DisplayList, ImpellerDisplayList);
 DEFINE_PEER_GETTER(DisplayListBuilder, ImpellerDisplayListBuilder);
+DEFINE_PEER_GETTER(GlyphInfo, ImpellerGlyphInfo);
 DEFINE_PEER_GETTER(ImageFilter, ImpellerImageFilter);
+DEFINE_PEER_GETTER(LineMetrics, ImpellerLineMetrics);
 DEFINE_PEER_GETTER(MaskFilter, ImpellerMaskFilter);
 DEFINE_PEER_GETTER(Paint, ImpellerPaint);
 DEFINE_PEER_GETTER(Paragraph, ImpellerParagraph);
@@ -1272,6 +1276,12 @@ uint32_t ImpellerParagraphGetLineCount(ImpellerParagraph paragraph) {
   return GetPeer(paragraph)->GetLineCount();
 }
 
+IMPELLER_EXTERN_C
+ImpellerRange ImpellerParagraphGetWordBoundary(ImpellerParagraph paragraph,
+                                               size_t code_unit_index) {
+  return GetPeer(paragraph)->GetWordBoundary(code_unit_index);
+}
+
 IMPELLER_EXTERN_C
 ImpellerTypographyContext ImpellerTypographyContextNew() {
   auto context = Create<TypographyContext>();
@@ -1309,4 +1319,155 @@ bool ImpellerTypographyContextRegisterFont(ImpellerTypographyContext context,
                                         family_name_alias);
 }
 
+IMPELLER_EXTERN_C
+ImpellerLineMetrics ImpellerParagraphGetLineMetrics(
+    ImpellerParagraph paragraph) {
+  return GetPeer(paragraph)->GetLineMetrics().GetC();
+}
+
+IMPELLER_EXTERN_C
+ImpellerGlyphInfo ImpellerParagraphCreateGlyphInfoAtCodeUnitIndexNew(
+    ImpellerParagraph paragraph,
+    size_t code_unit_index) {
+  return GetPeer(paragraph)
+      ->GetGlyphInfoAtCodeUnitIndex(code_unit_index)
+      .Leak();
+}
+
+IMPELLER_EXTERN_C
+ImpellerGlyphInfo ImpellerParagraphCreateGlyphInfoAtParagraphCoordinatesNew(
+    ImpellerParagraph paragraph,
+    double x,
+    double y) {
+  return GetPeer(paragraph)
+      ->GetClosestGlyphInfoAtParagraphCoordinates(x, y)
+      .Leak();
+}
+
+//------------------------------------------------------------------------------
+// Line Metrics
+//------------------------------------------------------------------------------
+
+IMPELLER_EXTERN_C
+void ImpellerLineMetricsRetain(ImpellerLineMetrics line_metrics) {
+  ObjectBase::SafeRetain(line_metrics);
+}
+
+IMPELLER_EXTERN_C
+void ImpellerLineMetricsRelease(ImpellerLineMetrics line_metrics) {
+  ObjectBase::SafeRelease(line_metrics);
+}
+
+IMPELLER_EXTERN_C
+double ImpellerLineMetricsGetUnscaledAscent(ImpellerLineMetrics metrics,
+                                            size_t line) {
+  return GetPeer(metrics)->GetUnscaledAscent(line);
+}
+
+IMPELLER_EXTERN_C
+double ImpellerLineMetricsGetAscent(ImpellerLineMetrics metrics, size_t line) {
+  return GetPeer(metrics)->GetAscent(line);
+}
+
+IMPELLER_EXTERN_C
+double ImpellerLineMetricsGetDescent(ImpellerLineMetrics metrics, size_t line) {
+  return GetPeer(metrics)->GetDescent(line);
+}
+
+IMPELLER_EXTERN_C
+double ImpellerLineMetricsGetBaseline(ImpellerLineMetrics metrics,
+                                      size_t line) {
+  return GetPeer(metrics)->GetBaseline(line);
+}
+
+IMPELLER_EXTERN_C
+bool ImpellerLineMetricsGetIsHardbreak(ImpellerLineMetrics metrics,
+                                       size_t line) {
+  return GetPeer(metrics)->GetIsHardbreak(line);
+}
+
+IMPELLER_EXTERN_C
+double ImpellerLineMetricsGetWidth(ImpellerLineMetrics metrics, size_t line) {
+  return GetPeer(metrics)->GetWidth(line);
+}
+
+IMPELLER_EXTERN_C
+double ImpellerLineMetricsGetHeight(ImpellerLineMetrics metrics, size_t line) {
+  return GetPeer(metrics)->GetHeight(line);
+}
+
+IMPELLER_EXTERN_C
+double ImpellerLineMetricsGetLeft(ImpellerLineMetrics metrics, size_t line) {
+  return GetPeer(metrics)->GetLeft(line);
+}
+
+IMPELLER_EXTERN_C
+size_t ImpellerLineMetricsGetCodeUnitStartIndex(ImpellerLineMetrics metrics,
+                                                size_t line) {
+  return GetPeer(metrics)->GetCodeUnitStartIndex(line);
+}
+
+IMPELLER_EXTERN_C
+size_t ImpellerLineMetricsGetCodeUnitEndIndex(ImpellerLineMetrics metrics,
+                                              size_t line) {
+  return GetPeer(metrics)->GetCodeUnitEndIndex(line);
+}
+
+IMPELLER_EXTERN_C
+size_t ImpellerLineMetricsGetCodeUnitEndIndexExcludingWhitespace(
+    ImpellerLineMetrics metrics,
+    size_t line) {
+  return GetPeer(metrics)->GetCodeUnitEndIndexExcludingWhitespace(line);
+}
+
+IMPELLER_EXTERN_C
+size_t ImpellerLineMetricsGetCodeUnitEndIndexIncludingNewline(
+    ImpellerLineMetrics metrics,
+    size_t line) {
+  return GetPeer(metrics)->GetCodeUnitEndIndexIncludingNewline(line);
+}
+
+//------------------------------------------------------------------------------
+// Glyph Info
+//------------------------------------------------------------------------------
+
+IMPELLER_EXTERN_C
+void ImpellerGlyphInfoRetain(ImpellerGlyphInfo glyph_info) {
+  ObjectBase::SafeRetain(glyph_info);
+}
+
+IMPELLER_EXTERN_C
+void ImpellerGlyphInfoRelease(ImpellerGlyphInfo glyph_info) {
+  ObjectBase::SafeRelease(glyph_info);
+}
+
+IMPELLER_EXTERN_C
+size_t ImpellerGlyphInfoGetGraphemeClusterCodeUnitRangeBegin(
+    ImpellerGlyphInfo glyph_info) {
+  return GetPeer(glyph_info)->GetGraphemeClusterCodeUnitRangeBegin();
+}
+
+IMPELLER_EXTERN_C
+size_t ImpellerGlyphInfoGetGraphemeClusterCodeUnitRangeEnd(
+    ImpellerGlyphInfo glyph_info) {
+  return GetPeer(glyph_info)->GetGraphemeClusterCodeUnitRangeEnd();
+}
+
+IMPELLER_EXTERN_C
+ImpellerRect ImpellerGlyphInfoGetGraphemeClusterBounds(
+    ImpellerGlyphInfo glyph_info) {
+  return GetPeer(glyph_info)->GetGraphemeClusterBounds();
+}
+
+IMPELLER_EXTERN_C
+bool ImpellerGlyphInfoIsEllipsis(ImpellerGlyphInfo glyph_info) {
+  return GetPeer(glyph_info)->IsEllipsis();
+}
+
+IMPELLER_EXTERN_C
+ImpellerTextDirection ImpellerGlyphInfoGetTextDirection(
+    ImpellerGlyphInfo glyph_info) {
+  return GetPeer(glyph_info)->GetTextDirection();
+}
+
 }  // namespace impeller::interop