impeller/typographer/backends/skia/text_render_context_skia.cc

// 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/typographer/backends/skia/text_render_context_skia.h"

#include <utility>

#include "flutter/fml/logging.h"
#include "flutter/fml/trace_event.h"
#include "impeller/base/allocation.h"
#include "impeller/renderer/allocator.h"
#include "impeller/typographer/backends/skia/typeface_skia.h"
#include "third_party/skia/include/core/SkBitmap.h"
#include "third_party/skia/include/core/SkCanvas.h"
#include "third_party/skia/include/core/SkFont.h"
#include "third_party/skia/include/core/SkFontMetrics.h"
#include "third_party/skia/include/core/SkRSXform.h"
#include "third_party/skia/include/core/SkSurface.h"
#include "third_party/skia/src/core/SkIPoint16.h"   // nogncheck
#include "third_party/skia/src/gpu/GrRectanizer.h"  // nogncheck

namespace impeller {

TextRenderContextSkia::TextRenderContextSkia(std::shared_ptr<Context> context)
    : TextRenderContext(std::move(context)) {}

TextRenderContextSkia::~TextRenderContextSkia() = default;

static FontGlyphPair::Set CollectUniqueFontGlyphPairsSet(
    GlyphAtlas::Type type,
    const TextRenderContext::FrameIterator& frame_iterator) {
  FontGlyphPair::Set set;
  while (auto frame = frame_iterator()) {
    for (const auto& run : frame->GetRuns()) {
      auto font = run.GetFont();
      // TODO(dnfield): If we're doing SDF here, we should be using a consistent
      // point size.
      // https://github.com/flutter/flutter/issues/112016
      for (const auto& glyph_position : run.GetGlyphPositions()) {
        set.insert({font, glyph_position.glyph});
      }
    }
  }
  return set;
}

static FontGlyphPair::Vector CollectUniqueFontGlyphPairs(
    GlyphAtlas::Type type,
    const TextRenderContext::FrameIterator& frame_iterator) {
  TRACE_EVENT0("impeller", __FUNCTION__);
  FontGlyphPair::Vector vector;
  auto set = CollectUniqueFontGlyphPairsSet(type, frame_iterator);
  vector.reserve(set.size());
  for (const auto& item : set) {
    vector.emplace_back(item);
  }
  return vector;
}

static size_t PairsFitInAtlasOfSize(const FontGlyphPair::Vector& pairs,
                                    const ISize& atlas_size,
                                    std::vector<Rect>& glyph_positions) {
  if (atlas_size.IsEmpty()) {
    return false;
  }

  auto rect_packer = std::unique_ptr<GrRectanizer>(
      GrRectanizer::Factory(atlas_size.width, atlas_size.height));

  glyph_positions.clear();
  glyph_positions.reserve(pairs.size());

  // TODO(114563): We might be able to remove this per-glyph padding if we fix
  //               the underlying causes of the overlap.
  constexpr auto padding = 2;

  for (size_t i = 0; i < pairs.size(); i++) {
    const auto& pair = pairs[i];
    const auto glyph_size =
        ISize::Ceil(pair.font.GetMetrics().GetBoundingBox().size *
                    pair.font.GetMetrics().scale);
    SkIPoint16 location_in_atlas;
    if (!rect_packer->addRect(glyph_size.width + padding,   //
                              glyph_size.height + padding,  //
                              &location_in_atlas            //
                              )) {
      return pairs.size() - i;
    }
    glyph_positions.emplace_back(Rect::MakeXYWH(location_in_atlas.x(),  //
                                                location_in_atlas.y(),  //
                                                glyph_size.width,       //
                                                glyph_size.height       //
                                                ));
  }

  return 0;
}

static ISize OptimumAtlasSizeForFontGlyphPairs(
    const FontGlyphPair::Vector& pairs,
    std::vector<Rect>& glyph_positions) {
  static constexpr auto kMinAtlasSize = 8u;
  static constexpr auto kMaxAtlasSize = 4096u;

  TRACE_EVENT0("impeller", __FUNCTION__);

  ISize current_size(kMinAtlasSize, kMinAtlasSize);
  size_t total_pairs = pairs.size() + 1;
  do {
    auto remaining_pairs =
        PairsFitInAtlasOfSize(pairs, current_size, glyph_positions);
    if (remaining_pairs == 0) {
      return current_size;
    } else if (remaining_pairs < std::ceil(total_pairs / 2)) {
      current_size = ISize::MakeWH(
          std::max(current_size.width, current_size.height),
          Allocation::NextPowerOfTwoSize(
              std::min(current_size.width, current_size.height) + 1));
    } else {
      current_size = ISize::MakeWH(
          Allocation::NextPowerOfTwoSize(current_size.width + 1),
          Allocation::NextPowerOfTwoSize(current_size.height + 1));
    }
  } while (current_size.width <= kMaxAtlasSize &&
           current_size.height <= kMaxAtlasSize);
  return ISize{0, 0};
}

/// Compute signed-distance field for an 8-bpp grayscale image (values greater
/// than 127 are considered "on") For details of this algorithm, see "The 'dead
/// reckoning' signed distance transform" [Grevera 2004]
static void ConvertBitmapToSignedDistanceField(uint8_t* pixels,
                                               uint16_t width,
                                               uint16_t height) {
  if (!pixels || width == 0 || height == 0) {
    return;
  }

  using ShortPoint = TPoint<uint16_t>;

  // distance to nearest boundary point map
  std::vector<Scalar> distance_map(width * height);
  // nearest boundary point map
  std::vector<ShortPoint> boundary_point_map(width * height);

  // Some helpers for manipulating the above arrays
#define image(_x, _y) (pixels[(_y)*width + (_x)] > 0x7f)
#define distance(_x, _y) distance_map[(_y)*width + (_x)]
#define nearestpt(_x, _y) boundary_point_map[(_y)*width + (_x)]

  const Scalar maxDist = hypot(width, height);
  const Scalar distUnit = 1;
  const Scalar distDiag = sqrt(2);

  // Initialization phase: set all distances to "infinity"; zero out nearest
  // boundary point map
  for (uint16_t y = 0; y < height; ++y) {
    for (uint16_t x = 0; x < width; ++x) {
      distance(x, y) = maxDist;
      nearestpt(x, y) = ShortPoint{0, 0};
    }
  }

  // Immediate interior/exterior phase: mark all points along the boundary as
  // such
  for (uint16_t y = 1; y < height - 1; ++y) {
    for (uint16_t x = 1; x < width - 1; ++x) {
      bool inside = image(x, y);
      if (image(x - 1, y) != inside || image(x + 1, y) != inside ||
          image(x, y - 1) != inside || image(x, y + 1) != inside) {
        distance(x, y) = 0;
        nearestpt(x, y) = ShortPoint{x, y};
      }
    }
  }

  // Forward dead-reckoning pass
  for (uint16_t y = 1; y < height - 2; ++y) {
    for (uint16_t x = 1; x < width - 2; ++x) {
      if (distance_map[(y - 1) * width + (x - 1)] + distDiag < distance(x, y)) {
        nearestpt(x, y) = nearestpt(x - 1, y - 1);
        distance(x, y) = hypot(x - nearestpt(x, y).x, y - nearestpt(x, y).y);
      }
      if (distance(x, y - 1) + distUnit < distance(x, y)) {
        nearestpt(x, y) = nearestpt(x, y - 1);
        distance(x, y) = hypot(x - nearestpt(x, y).x, y - nearestpt(x, y).y);
      }
      if (distance(x + 1, y - 1) + distDiag < distance(x, y)) {
        nearestpt(x, y) = nearestpt(x + 1, y - 1);
        distance(x, y) = hypot(x - nearestpt(x, y).x, y - nearestpt(x, y).y);
      }
      if (distance(x - 1, y) + distUnit < distance(x, y)) {
        nearestpt(x, y) = nearestpt(x - 1, y);
        distance(x, y) = hypot(x - nearestpt(x, y).x, y - nearestpt(x, y).y);
      }
    }
  }

  // Backward dead-reckoning pass
  for (uint16_t y = height - 2; y >= 1; --y) {
    for (uint16_t x = width - 2; x >= 1; --x) {
      if (distance(x + 1, y) + distUnit < distance(x, y)) {
        nearestpt(x, y) = nearestpt(x + 1, y);
        distance(x, y) = hypot(x - nearestpt(x, y).x, y - nearestpt(x, y).y);
      }
      if (distance(x - 1, y + 1) + distDiag < distance(x, y)) {
        nearestpt(x, y) = nearestpt(x - 1, y + 1);
        distance(x, y) = hypot(x - nearestpt(x, y).x, y - nearestpt(x, y).y);
      }
      if (distance(x, y + 1) + distUnit < distance(x, y)) {
        nearestpt(x, y) = nearestpt(x, y + 1);
        distance(x, y) = hypot(x - nearestpt(x, y).x, y - nearestpt(x, y).y);
      }
      if (distance(x + 1, y + 1) + distDiag < distance(x, y)) {
        nearestpt(x, y) = nearestpt(x + 1, y + 1);
        distance(x, y) = hypot(x - nearestpt(x, y).x, y - nearestpt(x, y).y);
      }
    }
  }

  // Interior distance negation pass; distances outside the figure are
  // considered negative
  // Also does final quantization.
  for (uint16_t y = 0; y < height; ++y) {
    for (uint16_t x = 0; x < width; ++x) {
      if (!image(x, y)) {
        distance(x, y) = -distance(x, y);
      }

      float norm_factor = 13.5;
      float dist = distance(x, y);
      float clamped_dist = fmax(-norm_factor, fmin(dist, norm_factor));
      float scaled_dist = clamped_dist / norm_factor;
      uint8_t quantized_value = ((scaled_dist + 1) / 2) * UINT8_MAX;
      pixels[y * width + x] = quantized_value;
    }
  }

#undef image
#undef distance
#undef nearestpt
}

static std::shared_ptr<SkBitmap> CreateAtlasBitmap(const GlyphAtlas& atlas,
                                                   const ISize& atlas_size) {
  TRACE_EVENT0("impeller", __FUNCTION__);
  auto bitmap = std::make_shared<SkBitmap>();
  SkImageInfo image_info;

  switch (atlas.GetType()) {
    case GlyphAtlas::Type::kSignedDistanceField:
    case GlyphAtlas::Type::kAlphaBitmap:
      image_info = SkImageInfo::MakeA8(atlas_size.width, atlas_size.height);
      break;
    case GlyphAtlas::Type::kColorBitmap:
      image_info =
          SkImageInfo::MakeN32Premul(atlas_size.width, atlas_size.height);
      break;
  }

  if (!bitmap->tryAllocPixels(image_info)) {
    return nullptr;
  }
  auto surface = SkSurface::MakeRasterDirect(bitmap->pixmap());
  if (!surface) {
    return nullptr;
  }
  auto canvas = surface->getCanvas();
  if (!canvas) {
    return nullptr;
  }

  atlas.IterateGlyphs([canvas](const FontGlyphPair& font_glyph,
                               const Rect& location) -> bool {
    const auto& metrics = font_glyph.font.GetMetrics();
    const auto position = SkPoint::Make(location.origin.x / metrics.scale,
                                        location.origin.y / metrics.scale);
    SkGlyphID glyph_id = font_glyph.glyph.index;

    SkFont sk_font(
        TypefaceSkia::Cast(*font_glyph.font.GetTypeface()).GetSkiaTypeface(),
        metrics.point_size);
    auto glyph_color = SK_ColorWHITE;

    SkPaint glyph_paint;
    glyph_paint.setColor(glyph_color);
    canvas->resetMatrix();
    canvas->scale(metrics.scale, metrics.scale);
    canvas->drawGlyphs(1u,         // count
                       &glyph_id,  // glyphs
                       &position,  // positions
                       SkPoint::Make(-metrics.min_extent.x,
                                     -metrics.ascent),  // origin
                       sk_font,                         // font
                       glyph_paint                      // paint
    );
    return true;
  });

  return bitmap;
}

static std::shared_ptr<Texture> UploadGlyphTextureAtlas(
    const std::shared_ptr<Allocator>& allocator,
    std::shared_ptr<SkBitmap> bitmap,
    const ISize& atlas_size,
    PixelFormat format) {
  TRACE_EVENT0("impeller", __FUNCTION__);
  if (!allocator) {
    return nullptr;
  }

  FML_DCHECK(bitmap != nullptr);
  const auto& pixmap = bitmap->pixmap();

  TextureDescriptor texture_descriptor;
  texture_descriptor.storage_mode = StorageMode::kHostVisible;
  texture_descriptor.format = format;
  texture_descriptor.size = atlas_size;

  if (pixmap.rowBytes() * pixmap.height() !=
      texture_descriptor.GetByteSizeOfBaseMipLevel()) {
    return nullptr;
  }

  auto texture = allocator->CreateTexture(texture_descriptor);
  if (!texture || !texture->IsValid()) {
    return nullptr;
  }
  texture->SetLabel("GlyphAtlas");

  auto mapping = std::make_shared<fml::NonOwnedMapping>(
      reinterpret_cast<const uint8_t*>(bitmap->getAddr(0, 0)),  // data
      texture_descriptor.GetByteSizeOfBaseMipLevel(),           // size
      [bitmap](auto, auto) mutable { bitmap.reset(); }          // proc
  );

  if (!texture->SetContents(mapping)) {
    return nullptr;
  }
  return texture;
}

std::shared_ptr<GlyphAtlas> TextRenderContextSkia::CreateGlyphAtlas(
    GlyphAtlas::Type type,
    std::shared_ptr<GlyphAtlasContext> atlas_context,
    FrameIterator frame_iterator) const {
  TRACE_EVENT0("impeller", __FUNCTION__);
  if (!IsValid()) {
    return nullptr;
  }
  auto last_atlas = atlas_context->GetGlyphAtlas();

  // ---------------------------------------------------------------------------
  // Step 1: Collect unique font-glyph pairs in the frame.
  // ---------------------------------------------------------------------------

  auto font_glyph_pairs = CollectUniqueFontGlyphPairs(type, frame_iterator);
  if (font_glyph_pairs.empty()) {
    return last_atlas;
  }

  // ---------------------------------------------------------------------------
  // Step 2: Determine if the atlas type and font glyph pairs are compatible
  //         with the current atlas and reuse if possible.
  // ---------------------------------------------------------------------------
  if (last_atlas->GetType() == type &&
      last_atlas->HasSamePairs(font_glyph_pairs)) {
    return last_atlas;
  }

  auto glyph_atlas = std::make_shared<GlyphAtlas>(type);
  atlas_context->UpdateGlyphAtlas(glyph_atlas);

  // ---------------------------------------------------------------------------
  // Step 3: Get the optimum size of the texture atlas.
  // ---------------------------------------------------------------------------
  std::vector<Rect> glyph_positions;
  const auto atlas_size =
      OptimumAtlasSizeForFontGlyphPairs(font_glyph_pairs, glyph_positions);
  if (atlas_size.IsEmpty()) {
    return nullptr;
  }

  // ---------------------------------------------------------------------------
  // Step 4: Find location of font-glyph pairs in the atlas. We have this from
  // the last step. So no need to do create another rect packer. But just do a
  // sanity check of counts. This could also be just an assertion as only a
  // construction issue would cause such a failure.
  // ---------------------------------------------------------------------------
  if (glyph_positions.size() != font_glyph_pairs.size()) {
    return nullptr;
  }

  // ---------------------------------------------------------------------------
  // Step 5: Record the positions in the glyph atlas.
  // ---------------------------------------------------------------------------
  for (size_t i = 0, count = glyph_positions.size(); i < count; i++) {
    glyph_atlas->AddTypefaceGlyphPosition(font_glyph_pairs[i],
                                          glyph_positions[i]);
  }

  // ---------------------------------------------------------------------------
  // Step 6: Draw font-glyph pairs in the correct spot in the atlas.
  // ---------------------------------------------------------------------------
  auto bitmap = CreateAtlasBitmap(*glyph_atlas, atlas_size);
  if (!bitmap) {
    return nullptr;
  }

  // ---------------------------------------------------------------------------
  // Step 7: Upload the atlas as a texture.
  // ---------------------------------------------------------------------------
  PixelFormat format;
  switch (type) {
    case GlyphAtlas::Type::kSignedDistanceField:
      ConvertBitmapToSignedDistanceField(
          reinterpret_cast<uint8_t*>(bitmap->getPixels()), atlas_size.width,
          atlas_size.height);
    case GlyphAtlas::Type::kAlphaBitmap:
      format = PixelFormat::kA8UNormInt;
      break;
    case GlyphAtlas::Type::kColorBitmap:
      format = PixelFormat::kR8G8B8A8UNormInt;
      break;
  }
  auto texture = UploadGlyphTextureAtlas(GetContext()->GetResourceAllocator(),
                                         bitmap, atlas_size, format);
  if (!texture) {
    return nullptr;
  }

  // ---------------------------------------------------------------------------
  // Step 8: Record the texture in the glyph atlas.
  // ---------------------------------------------------------------------------
  glyph_atlas->SetTexture(std::move(texture));

  return glyph_atlas;
}

}  // namespace impeller