libtxt: If no glyphs were rendered, then compute baseline metrics usi…

…ng the paragraph style's font (flutter#4462)

Fixes the "empty text baseline" case in text_painter_rtl_test

third_party/txt/src/txt/paragraph.cc

@@ -99,10 +99,14 @@ bool GetItalic(const TextStyle& style) {
   }
 }
 
+minikin::FontStyle GetMinikinFontStyle(const TextStyle& style) {
+  return minikin::FontStyle(GetWeight(style), GetItalic(style));
+}
+
 void GetFontAndMinikinPaint(const TextStyle& style,
                             minikin::FontStyle* font,
                             minikin::MinikinPaint* paint) {
-  *font = minikin::FontStyle(GetWeight(style), GetItalic(style));
+  *font = GetMinikinFontStyle(style);
   paint->size = style.font_size;
   // Divide by font size so letter spacing is pixels, not proportional to font
   // size.
@@ -115,8 +119,14 @@ void GetFontAndMinikinPaint(const TextStyle& style,
   paint->paintFlags |= minikin::LinearTextFlag;
 }
 
-void GetPaint(const TextStyle& style, SkPaint* paint) {
-  paint->setTextSize(style.font_size);
+sk_sp<SkTypeface> GetDefaultSkiaTypeface(
+    const std::shared_ptr<txt::FontCollection>& font_collection,
+    const TextStyle& style) {
+  std::shared_ptr<minikin::FontCollection> collection =
+      font_collection->GetMinikinFontCollectionForFamily(style.font_family);
+  minikin::FakedFont faked_font =
+      collection->baseFontFaked(GetMinikinFontStyle(style));
+  return static_cast<FontSkia*>(faked_font.font)->GetSkTypeface();
 }
 
 void FindWords(const std::vector<uint16_t>& text,
@@ -258,6 +268,9 @@ bool Paragraph::ComputeLineBreaks() {
 }
 
 bool Paragraph::ComputeBidiRuns(std::vector<BidiRun>* result) {
+  if (text_.empty())
+    return true;
+
   auto ubidi_closer = [](UBiDi* b) { ubidi_close(b); };
   std::unique_ptr<UBiDi, decltype(ubidi_closer)> bidi(ubidi_open(),
                                                       ubidi_closer);
@@ -406,7 +419,7 @@ void Paragraph::Layout(double width, bool force) {
       minikin::FontStyle font;
       minikin::MinikinPaint minikin_paint;
       GetFontAndMinikinPaint(run.style, &font, &minikin_paint);
-      GetPaint(run.style, &paint);
+      paint.setTextSize(run.style.font_size);
 
       std::shared_ptr<minikin::FontCollection> minikin_font_collection =
           font_collection_->GetMinikinFontCollectionForFamily(
@@ -467,16 +480,8 @@ void Paragraph::Layout(double width, bool force) {
       layout.doLayout(text_ptr, text_start, text_count, text_.size(), bidiFlags,
                       font, minikin_paint, minikin_font_collection);
 
-      if (layout.nGlyphs() == 0) {
-        // This run is empty, so insert a placeholder paint record that captures
-        // the current font metrics.
-        SkPaint::FontMetrics metrics;
-        paint.getFontMetrics(&metrics);
-        paint_records.emplace_back(run.style, SkPoint::Make(run_x_offset, 0),
-                                   builder.make(), metrics, line_number,
-                                   layout.getAdvance());
+      if (layout.nGlyphs() == 0)
         continue;
-      }
 
       // Break the layout into blobs that share the same SkPaint parameters.
       std::vector<Range<size_t>> glyph_blobs;
@@ -604,26 +609,38 @@ void Paragraph::Layout(double width, bool force) {
 
     double max_line_spacing = 0;
     double max_descent = 0;
-    for (const PaintRecord& paint_record : paint_records) {
-      const SkPaint::FontMetrics& metrics = paint_record.metrics();
-      double style_height = paint_record.style().height;
+    auto update_line_metrics = [&](const SkPaint::FontMetrics& metrics,
+                                   const TextStyle& style) {
       double line_spacing =
           (line_number == 0)
-              ? -metrics.fAscent * style_height
-              : (-metrics.fAscent + metrics.fLeading) * style_height;
+              ? -metrics.fAscent * style.height
+              : (-metrics.fAscent + metrics.fLeading) * style.height;
       if (line_spacing > max_line_spacing) {
         max_line_spacing = line_spacing;
         if (line_number == 0) {
           alphabetic_baseline_ = line_spacing;
           // TODO(garyq): Properly implement ideographic_baseline_.
           ideographic_baseline_ =
-              (metrics.fUnderlinePosition - metrics.fAscent) * style_height;
+              (metrics.fUnderlinePosition - metrics.fAscent) * style.height;
         }
       }
       max_line_spacing = std::max(line_spacing, max_line_spacing);
 
-      double descent = metrics.fDescent * style_height;
+      double descent = metrics.fDescent * style.height;
       max_descent = std::max(descent, max_descent);
+    };
+    for (const PaintRecord& paint_record : paint_records) {
+      update_line_metrics(paint_record.metrics(), paint_record.style());
+    }
+    // If no fonts were actually rendered, then compute a baseline based on the
+    // font of the paragraph style.
+    if (paint_records.empty()) {
+      SkPaint::FontMetrics metrics;
+      TextStyle style(paragraph_style_.GetTextStyle());
+      paint.setTypeface(GetDefaultSkiaTypeface(font_collection_, style));
+      paint.setTextSize(style.font_size);
+      paint.getFontMetrics(&metrics);
+      update_line_metrics(metrics, style);
     }
 
     line_heights_.push_back((line_heights_.empty() ? 0 : line_heights_.back()) +

third_party/txt/src/txt/paragraph_style.cc

@@ -18,6 +18,13 @@
 
 namespace txt {
 
-//
+TextStyle ParagraphStyle::GetTextStyle() const {
+  TextStyle result;
+  result.font_weight = font_weight;
+  result.font_style = font_style;
+  result.font_family = font_family;
+  result.font_size = font_size;
+  return result;
+}
 
 }  // namespace txt

third_party/txt/src/txt/paragraph_style.h

@@ -23,6 +23,7 @@
 #include "font_style.h"
 #include "font_weight.h"
 #include "minikin/LineBreaker.h"
+#include "text_style.h"
 
 namespace txt {
 
@@ -58,6 +59,8 @@ class ParagraphStyle {
   // kBreakStrategy_Balanced will balance between the two.
   minikin::BreakStrategy break_strategy =
       minikin::BreakStrategy::kBreakStrategy_Greedy;
+
+  TextStyle GetTextStyle() const;
 };
 
 }  // namespace txt

third_party/txt/tests/paragraph_unittests.cc

@@ -1345,7 +1345,7 @@ TEST_F(ParagraphTest, DISABLE_ON_WINDOWS(NewlineParagraph)) {
 
   ASSERT_TRUE(Snapshot());
 
-  ASSERT_EQ(paragraph->records_.size(), 7ull);
+  ASSERT_EQ(paragraph->records_.size(), 6ull);
   EXPECT_DOUBLE_EQ(paragraph->records_[0].offset().x(), 0);
   EXPECT_DOUBLE_EQ(paragraph->records_[1].offset().x(), 0);
   EXPECT_DOUBLE_EQ(paragraph->records_[1].offset().y(), 126);
@@ -1354,7 +1354,6 @@ TEST_F(ParagraphTest, DISABLE_ON_WINDOWS(NewlineParagraph)) {
   EXPECT_DOUBLE_EQ(paragraph->records_[4].offset().x(), 0);
   EXPECT_DOUBLE_EQ(paragraph->records_[3].offset().y(), 266);
   EXPECT_DOUBLE_EQ(paragraph->records_[5].offset().x(), 0);
-  EXPECT_DOUBLE_EQ(paragraph->records_[6].offset().x(), 0);
 }
 
 TEST_F(ParagraphTest, DISABLE_ON_WINDOWS(EmojiParagraph)) {