add layer alpha interface to ios and andriod fix format

Author: leiyue123

android/libpag/src/main/java/org/libpag/PAGLayer.java

@@ -178,6 +178,11 @@ public Matrix getTotalMatrix() {
      */
     public native void setAlpha(float value);
 
+    /**
+    * Returns the current alpha of the layer if previously set.
+    */
+    public native float alpha();
+
     private native void nativeRelease();
 
     protected long nativeContext;

src/platform/android/JPAGLayer.cpp

@@ -298,13 +298,21 @@ PAG_API void Java_org_libpag_PAGLayer_setExcludedFromTimeline(JNIEnv* env, jobje
   pagLayer->setExcludedFromTimeline(value);
 }
 
- PAG_API void Java_org_libpag_PAGLayer_setAlpha(JNIEnv* env, jobject thiz,
-                                                jfloat value){
+PAG_API void Java_org_libpag_PAGLayer_setAlpha(JNIEnv* env, jobject thiz, jfloat value) {
   auto pagLayer = GetPAGLayer(env, thiz);
-  if(pagLayer == nullptr){
+  if (pagLayer == nullptr) {
     return;
   }
 
   pagLayer->setAlpha(value);
 }
+
+PAG_API jfloat Java_org_libpag_PAGLayer_alpha(JNIEnv* env, jobject thiz) {
+  auto pagLayer = GetPAGLayer(env, thiz);
+  if (pagLayer == nullptr) {
+    return 0.0f;
+  }
+
+  return pagLayer->alpha();
+}
 }

src/platform/cocoa/PAGLayer.h

@@ -171,4 +171,9 @@ PAG_API @interface PAGLayer : NSObject
  */
 - (void)setAlpha:(float)value;
 
+/**
+ * Returns the current alpha of the layer if previously set.
+ */
+- (float)alpha;
+
 @end

src/platform/cocoa/PAGLayer.m

@@ -133,10 +133,14 @@ - (void)setExcludedFromTimeline:(BOOL)value {
   [(PAGLayerImpl*)_impl setExcludedFromTimeline:value];
 }
 
-- (void)setAlpha:(float)value{
+- (void)setAlpha:(float)value {
   [(PAGLayerImpl*)_impl setAlpha:value];
 }
 
+- (float)alpha {
+  return [(PAGLayerImpl*)_impl alpha];
+}
+
 - (void)dealloc {
   [_impl release];
   [super dealloc];

src/platform/cocoa/private/PAGLayerImpl.h

@@ -74,4 +74,6 @@
 
 - (void)setAlpha:(float)value;
 
+- (float)alpha;
+
 @end

src/platform/cocoa/private/PAGLayerImpl.mm

@@ -258,4 +258,8 @@ - (void)setAlpha:(float)value {
   _pagLayer->setAlpha(value);
 }
 
+- (float)alpha {
+  return _pagLayer->alpha();
+}
+
 @end