[Qt] Implement LocalGlyphRasterizer

platform/qt/qt.cmake

@@ -29,6 +29,7 @@ set(MBGL_QT_CORE_FILES
     # Platform integration
     PRIVATE platform/qt/src/async_task.cpp
     PRIVATE platform/qt/src/async_task_impl.hpp
+    PRIVATE platform/qt/src/local_glyph_rasterizer.cpp
     PRIVATE platform/qt/src/qt_logging.cpp
     PRIVATE platform/qt/src/qt_image.cpp
     PRIVATE platform/qt/src/run_loop.cpp
@@ -38,7 +39,6 @@ set(MBGL_QT_CORE_FILES
     PRIVATE platform/qt/src/timer_impl.hpp
     PRIVATE platform/qt/src/utf.cpp
 
-    PRIVATE platform/default/src/mbgl/text/local_glyph_rasterizer.cpp
     PRIVATE platform/default/src/mbgl/text/collator.cpp
     PRIVATE platform/default/src/mbgl/text/unaccent.cpp
     PRIVATE platform/default/include/mbgl/text/unaccent.hpp

platform/qt/src/local_glyph_rasterizer.cpp

@@ -0,0 +1,74 @@
+#include <mbgl/text/local_glyph_rasterizer.hpp>
+#include <mbgl/util/i18n.hpp>
+
+#include <QtCore/QFile>
+#include <QtGui/QFont>
+#include <QtGui/QImage>
+#include <QtGui/QPainter>
+#include <qglobal.h>
+
+namespace mbgl {
+
+class LocalGlyphRasterizer::Impl {
+public:
+    Impl(const optional<std::string> fontFamily_);
+
+    bool isConfigured() const;
+
+    optional<std::string> fontFamily;
+    QFont font;
+};
+
+LocalGlyphRasterizer::Impl::Impl(const optional<std::string> fontFamily_)
+    : fontFamily(fontFamily_) {
+    if (isConfigured()) {
+        font.setFamily(QString::fromStdString(*fontFamily));
+        font.setPixelSize(24);
+    }
+}
+
+bool LocalGlyphRasterizer::Impl::isConfigured() const {
+    return fontFamily.operator bool();
+}
+
+LocalGlyphRasterizer::LocalGlyphRasterizer(const optional<std::string> fontFamily)
+    : impl(std::make_unique<Impl>(fontFamily)) {
+}
+
+LocalGlyphRasterizer::~LocalGlyphRasterizer() {
+}
+
+bool LocalGlyphRasterizer::canRasterizeGlyph(const FontStack&, GlyphID glyphID) {
+    return util::i18n::allowsFixedWidthGlyphGeneration(glyphID) && impl->isConfigured();
+}
+
+Glyph LocalGlyphRasterizer::rasterizeGlyph(const FontStack&, GlyphID glyphID) {
+    Glyph glyph;
+    glyph.id = glyphID;
+
+    QFontMetrics metrics(impl->font);
+    Size size(metrics.width(glyphID), metrics.height());
+
+    glyph.metrics.width = size.width;
+    glyph.metrics.height = size.height;
+    glyph.metrics.left = 3;
+    glyph.metrics.top = -8;
+    glyph.metrics.advance = metrics.width(glyphID);
+
+    QImage image(QSize(size.width, size.height), QImage::Format_Alpha8);
+    image.fill(qRgba(0, 0, 0, 0));
+
+    QPainter painter(&image);
+    painter.setFont(impl->font);
+    painter.setRenderHints(QPainter::TextAntialiasing);
+    painter.drawText(QPointF(0, metrics.ascent()), QString(QChar(glyphID)));
+
+    auto img = std::make_unique<uint8_t[]>(image.byteCount());
+    memcpy(img.get(), image.constBits(), image.byteCount());
+
+    glyph.bitmap = AlphaImage { size, std::move(img) };
+
+    return glyph;
+}
+
+} // namespace mbgl

test/text/local_glyph_rasterizer.test.cpp

@@ -52,7 +52,8 @@ public:
 
 } // end namespace
 
-#ifdef __APPLE__
+// Enabling Qt requires adding a CJK-compatible font in the CI image.
+#if defined(__APPLE__)
 
 TEST(LocalGlyphRasterizer, PingFang) {
     LocalGlyphRasterizerTest test(std::string("PingFang"));
@@ -64,10 +65,14 @@ TEST(LocalGlyphRasterizer, PingFang) {
         return response;
     };
     test.map.getStyle().loadJSON(util::read_file("test/fixtures/local_glyphs/mixed.json"));
+#if defined(__APPLE__)
     test.checkRendering("ping_fang");
+#elif defined(__QT__)
+    test.checkRendering("ping_fang_qt");
+#endif // defined(__APPLE__)
 }
 
-#endif
+#endif // defined(__APPLE__)
 
 TEST(LocalGlyphRasterizer, NoLocal) {
     // Expectation: without any local fonts set, and without any CJK glyphs provided,