make android.text.Layout.draw() compatible custom Canvas classes

TextAndroidCanvas is a proxy canvas class which prevents us from
accessing the GtkSnapshot of the real canvas. To solve this problem, we
call Canvas.drawText() for each line.

src/api-impl-jni/generated_headers/android_text_Layout.h

@@ -143,6 +143,14 @@ JNIEXPORT jint JNICALL Java_android_text_Layout_native_1get_1ellipsis_1count
 JNIEXPORT void JNICALL Java_android_text_Layout_native_1draw
   (JNIEnv *, jobject, jlong, jlong, jlong);
 
+/*
+ * Class:     android_text_Layout
+ * Method:    native_draw_custom_canvas
+ * Signature: (JLandroid/graphics/Canvas;Landroid/graphics/Paint;)V
+ */
+JNIEXPORT void JNICALL Java_android_text_Layout_native_1draw_1custom_1canvas
+  (JNIEnv *, jobject, jlong, jobject, jobject);
+
 #ifdef __cplusplus
 }
 #endif

src/api-impl-jni/graphics/android_graphics_GskCanvas.c

@@ -104,7 +104,7 @@ JNIEXPORT void JNICALL Java_android_graphics_GskCanvas_native_1drawText(JNIEnv *
 	(*env)->ReleaseStringUTFChars(env, text, str);
 	PangoRectangle rect;
 	pango_layout_get_pixel_extents(layout, NULL, &rect);
-	y -= rect.height;
+	y -= (float)pango_layout_get_baseline(layout) / PANGO_SCALE;
 	if (paint->alignment == PANGO_ALIGN_CENTER)
 		x -= rect.width / 2.f;
 	else if (paint->alignment == PANGO_ALIGN_RIGHT)

src/api-impl-jni/text/android_text_Layout.c

@@ -2,6 +2,7 @@
 #include <pango/pango.h>
 
 #include "../defines.h"
+#include "../util.h"
 #include "../graphics/AndroidPaint.h"
 #include "../generated_headers/android_text_Layout.h"
 
@@ -149,3 +150,22 @@ JNIEXPORT void JNICALL Java_android_text_Layout_native_1draw(JNIEnv *env, jobjec
 
 	gtk_snapshot_append_layout(snapshot, pango_layout, &android_paint->color);
 }
+
+JNIEXPORT void JNICALL Java_android_text_Layout_native_1draw_1custom_1canvas(JNIEnv *env, jobject object, jlong layout, jobject canvas, jobject paint)
+{
+	PangoLayout *pango_layout = PANGO_LAYOUT(_PTR(layout));
+
+	const gchar *text = pango_layout_get_text(pango_layout);
+	PangoLayoutIter *pango_iter = pango_layout_get_iter(pango_layout);
+	do {
+		PangoLayoutLine *pango_line = pango_layout_iter_get_line_readonly(pango_iter);
+
+		jstring text_jstr = (*env)->NewStringUTF(env, text + pango_line->start_index);
+		jint end = (*env)->GetStringLength(env, text_jstr);
+		if (pango_line->length < end)
+			end = pango_line->length;
+		jfloat y = (float)pango_layout_iter_get_baseline(pango_iter) / PANGO_SCALE;
+		(*env)->CallVoidMethod(env, canvas, handle_cache.canvas.drawText, text_jstr, (jint)0, end, (jfloat)0, y, paint);
+		(*env)->DeleteLocalRef(env, text_jstr);
+	} while (pango_layout_iter_next_line(pango_iter));
+}

src/api-impl-jni/util.c

@@ -175,6 +175,9 @@ void set_up_handle_cache(JNIEnv *env)
 	handle_cache.webview.class = _REF((*env)->FindClass(env, "android/webkit/WebView"));
 	handle_cache.webview.internalGetAssetManager = _METHOD(handle_cache.webview.class, "internalGetAssetManager", "()Landroid/content/res/AssetManager;");
 	handle_cache.webview.internalLoadChanged = _METHOD(handle_cache.webview.class, "internalLoadChanged", "(ILjava/lang/String;)V");
+
+	handle_cache.canvas.class = _REF((*env)->FindClass(env, "android/graphics/Canvas"));
+	handle_cache.canvas.drawText = _METHOD(handle_cache.canvas.class, "drawText", "(Ljava/lang/CharSequence;IIFFLandroid/graphics/Paint;)V");
 }
 
 void extract_from_apk(const char *path, const char *target) {

src/api-impl-jni/util.h

@@ -128,6 +128,10 @@ struct handle_cache {
 		jmethodID onCreate;
 		jmethodID start;
 	} instrumentation;
+	struct {
+		jclass class;
+		jmethodID drawText;
+	} canvas;
 };
 
 extern struct handle_cache handle_cache;