renderer: destroy engines safely.

Introduced a reference count to destroy it safely.

src/renderer/tvgCanvas.h

@@ -35,6 +35,7 @@ struct Canvas::Impl
 
     Impl(RenderMethod* pRenderer) : renderer(pRenderer)
     {
+        renderer->ref();
     }
 
     ~Impl()
@@ -47,9 +48,7 @@ struct Canvas::Impl
 
         clearPaints();
 
-        if (renderer) {
-            if ((--renderer->refCnt) == 0) delete(renderer);
-        }
+        if (renderer && (renderer->unref() == 0)) delete(renderer);
     }
 
     void clearPaints()

src/renderer/tvgPaint.cpp

@@ -223,7 +223,7 @@ RenderData Paint::Impl::update(RenderMethod* renderer, const RenderTransform* pT
 {
     if (this->renderer != renderer) {
         if (this->renderer) TVGERR("RENDERER", "paint's renderer has been changed!");
-        ++renderer->refCnt;
+        renderer->ref();
         this->renderer = renderer;
     }
 

src/renderer/tvgPaint.h

@@ -56,7 +56,7 @@ namespace tvg
         uint8_t ctxFlag = ContextFlag::Invalid;
         uint8_t id;
         uint8_t opacity = 255;
-        uint8_t refCnt = 0;
+        uint8_t refCnt = 0;                              //reference count
 
         Impl(Paint* pnt) : paint(pnt) {}
 
@@ -67,18 +67,19 @@ namespace tvg
                 free(compData);
             }
             delete(rTransform);
+            if (renderer && (renderer->unref() == 0)) delete(renderer);
         }
 
         uint8_t ref()
         {
             if (refCnt == 255) TVGERR("RENDERER", "Corrupted reference count!");
-            return (++refCnt);
+            return ++refCnt;
         }
 
         uint8_t unref()
         {
             if (refCnt == 0) TVGERR("RENDERER", "Corrupted reference count!");
-            return (--refCnt);
+            return --refCnt;
         }
 
         bool transform(const Matrix& m)

src/renderer/tvgRender.h

@@ -261,7 +261,23 @@ struct RenderShape
 
 class RenderMethod
 {
+private:
+    uint32_t refCnt = 0;        //reference count
+    Key key;
+
 public:
+    uint32_t ref()
+    {
+        ScopedLock lock(key);
+        return (++refCnt);
+    }
+
+    uint32_t unref()
+    {
+        ScopedLock lock(key);
+        return (--refCnt);
+    }
+
     virtual ~RenderMethod() {}
     virtual RenderData prepare(const RenderShape& rshape, RenderData data, const RenderTransform* transform, Array<RenderData>& clips, uint8_t opacity, RenderUpdateFlag flags, bool clipper) = 0;
     virtual RenderData prepare(const Array<RenderData>& scene, RenderData data, const RenderTransform* transform, Array<RenderData>& clips, uint8_t opacity, RenderUpdateFlag flags) = 0;