[android] Android implementation of local CJK glyph rendering

- Draws bold version of glyph if font stack contains string "bold"
 - Not hooked up to global configuration yet

platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/text/LocalGlyphRasterizer.java

@@ -0,0 +1,46 @@
+package com.mapbox.mapboxsdk.text;
+
+import android.graphics.Canvas;
+import android.graphics.Paint;
+import android.graphics.Bitmap;
+import android.graphics.Typeface;
+import android.support.annotation.WorkerThread;
+
+/**
+ * LocalGlyphRasterizer is the Android-specific platform implementation used
+ * by the portable local_glyph_rasterizer.hpp
+ */
+public class LocalGlyphRasterizer {
+
+  /***
+   * Uses Android-native drawing code to rasterize a single glyph
+   * to a square @{link Bitmap} which can be returned to portable
+   * code for transformation into a Signed Distance Field glyph.
+   *
+   * @param fontFamily Font family string to pass to Typeface.create
+   * @param bold If true, use Typeface.BOLD option
+   * @param glyphID 16-bit Unicode BMP codepoint to draw
+   *
+   * @return Return a @{link Bitmap} to be displayed in the requested tile.
+   */
+  @WorkerThread
+  protected static Bitmap drawGlyphBitmap(String fontFamily, boolean bold, char glyphID) {
+    /*
+      35x35px dimensions are hardwired to match local_glyph_rasterizer.cpp
+      These dimensions are large enough to draw a 24 point character in the middle
+      of the bitmap (y: 20) with some buffer around the edge
+    */
+    Bitmap bitmap = Bitmap.createBitmap(35, 35, Bitmap.Config.ARGB_8888);
+
+    Paint paint = new Paint();
+    paint.setAntiAlias(true);
+    paint.setTextSize(24);
+    paint.setTypeface(Typeface.create(fontFamily, bold ? Typeface.BOLD : Typeface.NORMAL));
+
+    Canvas canvas = new Canvas();
+    canvas.setBitmap(bitmap);
+    canvas.drawText(String.valueOf(glyphID), 0, 20, paint);
+
+    return bitmap;
+  }
+}

platform/android/config.cmake

@@ -32,11 +32,12 @@ macro(mbgl_platform_core)
         PRIVATE platform/android/src/timer.cpp
 
         # Misc
+        PRIVATE platform/android/src/text/local_glyph_rasterizer_jni.hpp
+        PRIVATE platform/android/src/text/local_glyph_rasterizer.cpp
         PRIVATE platform/android/src/logging_android.cpp
         PRIVATE platform/android/src/thread.cpp
         PRIVATE platform/default/string_stdlib.cpp
         PRIVATE platform/default/bidi.cpp
-        PRIVATE platform/default/local_glyph_rasterizer.cpp
         PRIVATE platform/default/thread_local.cpp
         PRIVATE platform/default/utf.cpp
 

platform/android/src/jni.cpp

@@ -51,6 +51,7 @@
 #include "style/light.hpp"
 #include "snapshotter/map_snapshotter.hpp"
 #include "snapshotter/map_snapshot.hpp"
+#include "text/local_glyph_rasterizer_jni.hpp"
 
 namespace mbgl {
 namespace android {
@@ -188,6 +189,9 @@ void registerNatives(JavaVM *vm) {
     // Snapshotter
     MapSnapshotter::registerNative(env);
     MapSnapshot::registerNative(env);
+
+    // text
+    LocalGlyphRasterizer::registerNative(env);
 }
 
 } // namespace android

platform/android/src/text/local_glyph_rasterizer.cpp

@@ -0,0 +1,126 @@
+#include <mbgl/text/local_glyph_rasterizer.hpp>
+#include <mbgl/util/i18n.hpp>
+#include <mbgl/util/platform.hpp>
+
+#include <jni/jni.hpp>
+
+#include "../attach_env.hpp"
+#include "../bitmap.hpp"
+
+#include "local_glyph_rasterizer_jni.hpp"
+
+/*
+    Android implementation of LocalGlyphRasterizer:
+     Draws CJK glyphs using locally available fonts.
+
+    Follows pattern of GL JS implementation in that:
+     - Only CJK glyphs are drawn locally (because we can guess their metrics effectively)
+        * Render size/metrics determined experimentally using Noto Sans
+     - Configuration is done at map creation time by setting a "font family"
+        * JS uses a CSS font-family, this uses android.graphics.Typeface
+          https://developer.android.com/reference/android/graphics/Typeface.html
+     - We use heuristics to extract a font-weight based on the incoming font stack
+        * JS tries to extract multiple weights, this implementation only looks for
+          "bold"
+
+     mbgl::LocalGlyphRasterizer is the portable interface
+     mbgl::LocalGlyphRasterizer::Impl stores platform-specific configuration data
+     mbgl::android::LocalGlyphRasterizer is the JNI wrapper
+     com.mapbox.mapboxsdk.text.LocalGlyphRasterizer is the Java implementation that
+      actually does the drawing
+ */
+
+namespace mbgl {
+namespace android {
+
+PremultipliedImage LocalGlyphRasterizer::drawGlyphBitmap(const std::string& fontFamily, const bool bold, const GlyphID glyphID) {
+    UniqueEnv env { AttachEnv() };
+
+    using Signature = jni::Object<Bitmap>(jni::String, jni::jboolean, jni::jchar);
+    auto method = javaClass.GetStaticMethod<Signature>(*env, "drawGlyphBitmap");
+
+    jni::String jniFontFamily = jni::Make<jni::String>(*env, fontFamily);
+
+    auto javaBitmap = javaClass.Call(*env,
+                                     method,
+                                     jniFontFamily,
+                                     static_cast<jni::jboolean>(bold),
+                                     static_cast<jni::jchar>(glyphID));
+
+    PremultipliedImage result = Bitmap::GetImage(*env, javaBitmap);
+    jni::DeleteLocalRef(*env, javaBitmap);
+    return result;
+}
+
+void LocalGlyphRasterizer::registerNative(jni::JNIEnv& env) {
+    javaClass = *jni::Class<LocalGlyphRasterizer>::Find(env).NewGlobalRef(env).release();
+}
+
+jni::Class<LocalGlyphRasterizer> LocalGlyphRasterizer::javaClass;
+
+} // namespace android
+
+class LocalGlyphRasterizer::Impl {
+public:
+    Impl(const optional<std::string> fontFamily_)
+        : fontFamily(fontFamily_)
+    {}
+
+    bool isConfigured() const {
+        return bool(fontFamily);
+    }
+
+    PremultipliedImage drawGlyphBitmap(const FontStack& fontStack, GlyphID glyphID) {
+        bool bold = false;
+        for (auto font : fontStack) {
+            std::string lowercaseFont = platform::lowercase(font);
+            if (lowercaseFont.find("bold") != std::string::npos) {
+                bold = true;
+            }
+        }
+        return android::LocalGlyphRasterizer::drawGlyphBitmap(*fontFamily, bold, glyphID);
+    }
+
+private:
+    optional<std::string> fontFamily;
+};
+
+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& fontStack, GlyphID glyphID) {
+    Glyph fixedMetrics;
+    if (!impl->isConfigured()) {
+        return fixedMetrics;
+    }
+
+    fixedMetrics.id = glyphID;
+
+    Size size(35, 35);
+
+    fixedMetrics.metrics.width = size.width;
+    fixedMetrics.metrics.height = size.height;
+    fixedMetrics.metrics.left = 3;
+    fixedMetrics.metrics.top = -10;
+    fixedMetrics.metrics.advance = 24;
+
+    PremultipliedImage rgbaBitmap = impl->drawGlyphBitmap(fontStack, glyphID);
+
+    // Copy alpha values from RGBA bitmap into the AlphaImage output
+    fixedMetrics.bitmap = AlphaImage(size);
+    for (uint32_t i = 0; i < size.width * size.height; i++) {
+        fixedMetrics.bitmap.data[i] = rgbaBitmap.data[4 * i + 3];
+    }
+
+    return fixedMetrics;
+}
+
+} // namespace mbgl

platform/android/src/text/local_glyph_rasterizer_jni.hpp

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <mbgl/util/image.hpp>
+
+#include <jni/jni.hpp>
+
+/*
+    android::LocalGlyphRasterizer is the JNI wrapper of
+    com/mapbox/mapboxsdk/text/LocalGlyphRasterizer
+
+    mbgl::LocalGlyphRasterizer is the portable interface
+    Both implementations are in local_glyph_rasterizer.cpp
+ */
+
+namespace mbgl {
+namespace android {
+
+class LocalGlyphRasterizer {
+public:
+    static PremultipliedImage drawGlyphBitmap(const std::string& fontFamily, const bool bold, const char16_t glyphID);
+
+    static constexpr auto Name() { return "com/mapbox/mapboxsdk/text/LocalGlyphRasterizer"; };
+
+    static jni::Class<LocalGlyphRasterizer> javaClass;
+
+    static void registerNative(jni::JNIEnv&);
+
+};
+
+} // namespace android
+} // namespace mbgl