Add SpriteTextBlob to improve the rendering of SpriteSheetFont with n…

…on-existent chars

To render text with a SpriteSheetFont we now create a SpriteTextBlob.
This blob can render non-existent code points using a default fallback
native font (SkiaFont) and create a chain of runs for each TextBlob
that use a different font.

In this way we don't change the whole appearance of the rendered text
with an antialiased font when a missing code point appears. We just
use the fallback font to render that specific code point/char (or
sequence of chars in one run).

This problem was reported several times and we can find examples here:
aseprite/aseprite#2890 (comment)

As a side note, all code/static functions that use a text shaper
(HarfBuzz, skshaper module, etc.) is separated in its own file
(i.e. translation unit) to make binary executable files smaller when
the shaper is not needed (e.g. in English-only apps).

examples/text_shape.cpp

@@ -45,14 +45,11 @@ struct TextEdit {
 
     // TextBlob::RunHandler impl
     void commitRunBuffer(TextBlob::RunInfo& info) override {
-      if (info.clusters &&
-          info.glyphCount > 0) {
-        Box box;
-        for (int i=0; i<info.glyphCount; ++i) {
-          box.utf8Range = info.getGlyphUtf8Range(i);
-          box.bounds = info.getGlyphBounds(i);
-          m_boxes.push_back(box);
-        }
+      Box box;
+      for (int i=0; i<info.glyphCount; ++i) {
+        box.utf8Range = info.getGlyphUtf8Range(i);
+        box.bounds = info.getGlyphBounds(i);
+        m_boxes.push_back(box);
       }
     }
 

os/skia/skia_helpers.h

@@ -9,6 +9,7 @@
 #pragma once
 
 #include "gfx/color.h"
+#include "gfx/point.h"
 #include "gfx/rect.h"
 #include "os/paint.h"
 #include "os/sampling.h"
@@ -30,6 +31,10 @@ inline SkColor4f to_skia4f(gfx::Color c) {
   return SkColor4f::FromColor(to_skia(c));
 }
 
+inline SkPoint to_skia(const gfx::PointF& pt) {
+  return SkPoint::Make(pt.x, pt.y);
+}
+
 inline SkIRect to_skia(const gfx::Rect& rc) {
   return SkIRect::MakeXYWH(rc.x, rc.y, rc.w, rc.h);
 }
@@ -38,6 +43,10 @@ inline SkRect to_skia(const gfx::RectF& rc) {
   return SkRect::MakeXYWH(SkScalar(rc.x), SkScalar(rc.y), SkScalar(rc.w), SkScalar(rc.h));
 }
 
+inline gfx::PointF from_skia(const SkPoint& pt) {
+  return gfx::PointF(pt.x(), pt.y());
+}
+
 inline gfx::RectF from_skia(const SkRect& rc) {
   return gfx::RectF(rc.x(), rc.y(), rc.width(), rc.height());
 }

text/CMakeLists.txt

@@ -5,8 +5,12 @@
 
 add_library(laf-text
   draw_text.cpp
+  draw_text_shaper.cpp
   font_mgr.cpp
-  text_blob.cpp)
+  sprite_text_blob.cpp
+  sprite_text_blob_shaper.cpp
+  text_blob.cpp
+  text_blob_shaper.cpp)
 
 target_link_libraries(laf-text laf-os laf-gfx laf-base)
 
@@ -18,11 +22,10 @@ endif()
 
 if(LAF_BACKEND STREQUAL "skia")
   target_sources(laf-text PRIVATE
-    skia_draw_text.cpp
     skia_font.cpp
     skia_font_mgr.cpp
     skia_text_blob.cpp
-    skia_with_shaper.cpp)
+    skia_text_blob_shaper.cpp)
   target_link_libraries(laf-text
     skia skshaper)
 else()