Add SkTypeface::openExistingStream.

Allow users to retrieve the stream from an SkTypeface, but only if that stream is inexpensive to create.

Bug: https://github.com/flutter/flutter/issues/97384

Change-Id: I9bab1a775273363500cf7482f1babeee75c5a3df
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/503349
Reviewed-by: Ben Wagner <bungeman@google.com>
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Julia Lavrova <jlavrova@google.com>

include/core/SkTypeface.h

@@ -319,6 +319,15 @@ public:
      */
     std::unique_ptr<SkStreamAsset> openStream(int* ttcIndex) const;
 
+    /**
+     * Return a stream for the contents of the font data.
+     * Returns nullptr on failure or if the font data isn't already available in stream form.
+     * Use when the stream can be used opportunistically but the calling code would prefer
+     * to fall back to table access if creating the stream would be expensive.
+     * Otherwise acts the same as openStream.
+     */
+    std::unique_ptr<SkStreamAsset> openExistingStream(int* ttcIndex) const;
+
     /**
      *  Return a scalercontext for the given descriptor. It may return a
      *  stub scalercontext that will not crash, but will draw nothing.
@@ -377,6 +386,8 @@ protected:
 
     virtual std::unique_ptr<SkStreamAsset> onOpenStream(int* ttcIndex) const = 0;
 
+    virtual std::unique_ptr<SkStreamAsset> onOpenExistingStream(int* ttcIndex) const;
+
     virtual bool onGlyphMaskNeedsCurrentColor() const = 0;
 
     virtual int onGetVariationDesignPosition(

modules/skshaper/src/SkShaper_harfbuzz.cpp

@@ -265,7 +265,7 @@ SkDEBUGCODE(static hb_user_data_key_t gDataIdKey;)
 
 HBFace create_hb_face(const SkTypeface& typeface) {
     int index = 0;
-    std::unique_ptr<SkStreamAsset> typefaceAsset = typeface.openStream(&index);
+    std::unique_ptr<SkStreamAsset> typefaceAsset = typeface.openExistingStream(&index);
     HBFace face;
     if (typefaceAsset && typefaceAsset->getMemoryBase()) {
         HBBlob blob(stream_to_blob(std::move(typefaceAsset)));

src/core/SkTypeface.cpp

@@ -290,6 +290,15 @@ std::unique_ptr<SkStreamAsset> SkTypeface::openStream(int* ttcIndex) const {
     return this->onOpenStream(ttcIndex);
 }
 
+std::unique_ptr<SkStreamAsset> SkTypeface::openExistingStream(int* ttcIndex) const {
+    int ttcIndexStorage;
+    if (nullptr == ttcIndex) {
+        // So our subclasses don't need to check for null param
+        ttcIndex = &ttcIndexStorage;
+    }
+    return this->onOpenExistingStream(ttcIndex);
+}
+
 std::unique_ptr<SkScalerContext> SkTypeface::createScalerContext(
         const SkScalerContextEffects& effects, const SkDescriptor* desc) const {
     std::unique_ptr<SkScalerContext> scalerContext = this->onCreateScalerContext(effects, desc);
@@ -438,6 +447,10 @@ bool SkTypeface::onGetKerningPairAdjustments(const uint16_t glyphs[], int count,
     return false;
 }
 
+std::unique_ptr<SkStreamAsset> SkTypeface::onOpenExistingStream(int* ttcIndex) const {
+    return this->onOpenStream(ttcIndex);
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 #include "include/core/SkPaint.h"

src/ports/SkTypeface_mac_ct.cpp

@@ -775,6 +775,11 @@ std::unique_ptr<SkStreamAsset> SkTypeface_Mac::onOpenStream(int* ttcIndex) const
     return fStream->duplicate();
 }
 
+std::unique_ptr<SkStreamAsset> SkTypeface_Mac::onOpenExistingStream(int* ttcIndex) const {
+    *ttcIndex = 0;
+    return fStream ? fStream->duplicate() : nullptr;
+}
+
 int SkTypeface_Mac::onGetVariationDesignPosition(
         SkFontArguments::VariationPosition::Coordinate coordinates[], int coordinateCount) const
 {

src/ports/SkTypeface_mac_ct.h

@@ -94,6 +94,7 @@ public:
 protected:
     int onGetUPEM() const override;
     std::unique_ptr<SkStreamAsset> onOpenStream(int* ttcIndex) const override;
+    std::unique_ptr<SkStreamAsset> onOpenExistingStream(int* ttcIndex) const override;
     bool onGlyphMaskNeedsCurrentColor() const override { return false; }
     int onGetVariationDesignPosition(SkFontArguments::VariationPosition::Coordinate coordinates[],
                                      int coordinateCount) const override;