[android] Reuse Bitmap, Paint & Canvas instances in LocalGlyphRasterizer

- Make LocalGlyphRasterizer.drawGlyphBitmap() non-static
- Store and reuse Bitmap, Paint & Canvas instances

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

@@ -1,8 +1,10 @@
 package com.mapbox.mapboxsdk.text;
 
 import android.graphics.Canvas;
+import android.graphics.Color;
 import android.graphics.Paint;
 import android.graphics.Bitmap;
+import android.graphics.PorterDuff;
 import android.graphics.Typeface;
 import android.support.annotation.Keep;
 import android.support.annotation.WorkerThread;
@@ -12,6 +14,25 @@ import android.support.annotation.WorkerThread;
  * by the portable local_glyph_rasterizer.hpp
  */
 public class LocalGlyphRasterizer {
+  private final Bitmap bitmap;
+  private final Paint paint;
+  private final Canvas canvas;
+
+  LocalGlyphRasterizer() {
+    /*
+      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.createBitmap(35, 35, Bitmap.Config.ARGB_8888);
+
+    paint = new Paint();
+    paint.setAntiAlias(true);
+    paint.setTextSize(24);
+
+    canvas = new Canvas();
+    canvas.setBitmap(bitmap);
+  }
 
   /***
    * Uses Android-native drawing code to rasterize a single glyph
@@ -26,23 +47,10 @@ public class LocalGlyphRasterizer {
    */
   @WorkerThread
   @Keep
-  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);
+  protected Bitmap drawGlyphBitmap(String fontFamily, boolean bold, char glyphID) {
     paint.setTypeface(Typeface.create(fontFamily, bold ? Typeface.BOLD : Typeface.NORMAL));
-
-    Canvas canvas = new Canvas();
-    canvas.setBitmap(bitmap);
+    canvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);
     canvas.drawText(String.valueOf(glyphID), 0, 20, paint);
-
     return bitmap;
   }
 }

platform/android/src/text/local_glyph_rasterizer.cpp

@@ -33,19 +33,27 @@
 namespace mbgl {
 namespace android {
 
+LocalGlyphRasterizer::LocalGlyphRasterizer() {
+    UniqueEnv env { AttachEnv() };
+
+    static auto constructor = javaClass.GetConstructor(*env);
+
+    javaObject = javaClass.New(*env, constructor).NewGlobalRef(*env);
+}
+
 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");
+    static auto method = javaClass.GetMethod<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));
+    auto javaBitmap = javaObject->Call(*env,
+                                       method,
+                                       jniFontFamily,
+                                       static_cast<jni::jboolean>(bold),
+                                       static_cast<jni::jchar>(glyphID));
     jni::DeleteLocalRef(*env, jniFontFamily);
 
     PremultipliedImage result = Bitmap::GetImage(*env, javaBitmap);
@@ -77,13 +85,15 @@ public:
             std::string lowercaseFont = platform::lowercase(font);
             if (lowercaseFont.find("bold") != std::string::npos) {
                 bold = true;
+                break;
             }
         }
-        return android::LocalGlyphRasterizer::drawGlyphBitmap(*fontFamily, bold, glyphID);
+        return androidLocalGlyphRasterizer.drawGlyphBitmap(*fontFamily, bold, glyphID);
     }
 
 private:
     optional<std::string> fontFamily;
+    android::LocalGlyphRasterizer androidLocalGlyphRasterizer;
 };
 
 LocalGlyphRasterizer::LocalGlyphRasterizer(const optional<std::string> fontFamily)

platform/android/src/text/local_glyph_rasterizer_jni.hpp

@@ -17,14 +17,18 @@ 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&);
 
+    LocalGlyphRasterizer();
+
+    PremultipliedImage drawGlyphBitmap(const std::string& fontFamily, const bool bold, const char16_t glyphID);
+
+private:
+    jni::UniqueObject<LocalGlyphRasterizer> javaObject;
 };
 
 } // namespace android