text_font_context.hpp

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// text_font_context.hpp — owns the per-context typeface registry used by
// Canvas2D `fillText/strokeText` (via SkShaper fallback runs) and by the
// `TextShaper` measurement path (via SkParagraph FontCollection).
//
// Why this exists:
//   - HarfBuzz can only shape a multi-codepoint emoji cluster (ZWJ, flag,
//     keycap, modifier, tag) if the whole cluster lands on one font run.
//     `emoji_segmenter` pre-segments the text, and `TextFontContext`
//     supplies the typeface for each role (Default vs Emoji).
//   - A process-wide singleton would let one plugin overwrite another's
//     fallback registration in the same host process. Instead each
//     `AssetManager` / `Canvas` owns a context; a `shared()` default is
//     available for plugin authors who haven't wired their own.
//   - `SkParagraph::ParagraphBuilder` needs a `FontCollection` for label
//     measurement; we cache one per context so it isn't reconstructed
//     every call.
//
// This header is Skia-aware and intentionally only ships under
// `PULP_HAS_SKIA`. Non-Skia callers should use the API stubs in
// `font_registry_stubs.cpp`.
 
#pragma once
 
#include <pulp/canvas/bundled_fonts.hpp>
#include <pulp/canvas/emoji_segmenter.hpp>
 
#include <cstdint>
#include <memory>
#include <mutex>
#include <string>
#include <vector>
 
#ifdef PULP_HAS_SKIA
 
#include "include/core/SkFontMgr.h"
#include "include/core/SkFontStyle.h"
#include "include/core/SkRefCnt.h"
#include "include/core/SkTypeface.h"
 
namespace skia { namespace textlayout {
class FontCollection;
class TypefaceFontProvider;
} }
 
namespace pulp::canvas {
 
class TextFontContext {
public:
    TextFontContext();
    ~TextFontContext();
 
    TextFontContext(const TextFontContext&) = delete;
    TextFontContext& operator=(const TextFontContext&) = delete;

    static std::shared_ptr<TextFontContext> shared();

    sk_sp<SkFontMgr> font_manager() const { return font_mgr_; }

    sk_sp<skia::textlayout::FontCollection> font_collection() const;

    std::unique_lock<std::mutex> lock_font_collection_use() const {
        return std::unique_lock<std::mutex>(font_collection_use_mutex_);
    }

    std::string emoji_family_name() const;

    void set_emoji_typeface(sk_sp<SkTypeface> face);

    sk_sp<SkTypeface> emoji_typeface() const;

    bool has_emoji_typeface() const;

    sk_sp<SkTypeface> typeface_for_run(FontRunRole role,
                                       const sk_sp<SkTypeface>& primary) const;
 
private:
    sk_sp<SkFontMgr> font_mgr_;
    sk_sp<SkTypeface> emoji_typeface_;
    std::string emoji_family_name_;
 
    mutable std::mutex mutex_;
    mutable std::mutex font_collection_use_mutex_;
    mutable sk_sp<skia::textlayout::FontCollection> font_collection_;
    mutable sk_sp<skia::textlayout::TypefaceFontProvider> typeface_provider_;
    mutable std::uint64_t collection_generation_ = 0;
};
 
// ── Public registration API ────────────────────────────────────────────

bool register_emoji_fallback(sk_sp<SkTypeface> face);

bool register_emoji_fallback(const std::string& family);

bool register_platform_emoji_fallback();

bool register_bundled_noto_color_emoji();

bool register_best_available_emoji_fallback();
 
} // namespace pulp::canvas
 
#else  // PULP_HAS_SKIA
 
namespace pulp::canvas {
// Non-Skia stubs so plugin startup code can call these unconditionally.
inline bool register_emoji_fallback(...) { return false; }
inline bool register_platform_emoji_fallback() { return false; }
inline bool register_bundled_noto_color_emoji() { return false; }
inline bool register_best_available_emoji_fallback() { return false; }
} // namespace pulp::canvas
 
#endif // PULP_HAS_SKIA