common canvas: revise clear method.

Canvas::clear() introduces a new argument "free" that deterimes freeing the retained paints.

If free is true, Canvas won't delete the retained paints so that user keep paints valid.

In this scenario, user must have paints pointers, free them manually or push them again to the canvas.

This scenario is useful if user wants to re-organize paints order in the list or reuse them.

inc/thorvg.h

@@ -148,7 +148,7 @@ public:
 
     Result reserve(uint32_t n) noexcept;
     virtual Result push(std::unique_ptr<Paint> paint) noexcept;
-    virtual Result clear() noexcept;
+    virtual Result clear(bool free = true) noexcept;
     virtual Result update(Paint* paint) noexcept;
     virtual Result draw() noexcept;
     virtual Result sync() noexcept;

src/lib/tvgBezier.cpp

@@ -147,4 +147,4 @@ void bezSplitAt(const Bezier& cur, float at, Bezier& left, Bezier& right)
     bezSplitLeft(right, t, left);
 }
 
-}
+}

src/lib/tvgCanvas.cpp

@@ -49,9 +49,9 @@ Result Canvas::push(unique_ptr<Paint> paint) noexcept
 }
 
 
-Result Canvas::clear() noexcept
+Result Canvas::clear(bool free) noexcept
 {
-    return pImpl->clear();
+    return pImpl->clear(free);
 }
 
 

src/lib/tvgCanvasImpl.h

@@ -40,7 +40,7 @@ struct Canvas::Impl
 
     ~Impl()
     {
-        clear();
+        clear(true);
         delete(renderer);
     }
 
@@ -53,16 +53,19 @@ struct Canvas::Impl
         return update(p);
     }
 
-    Result clear()
+    Result clear(bool free)
     {
         if (!renderer) return Result::InsufficientCondition;
 
         //Clear render target before drawing
         if (!renderer->clear()) return Result::InsufficientCondition;
 
-        for (auto paint : paints) {
-            paint->pImpl->dispose(*renderer);
-            delete(paint);
+        //free paints
+        if (free) {
+            for (auto paint : paints) {
+                paint->pImpl->dispose(*renderer);
+                delete(paint);
+            }
         }
 
         paints.clear();
@@ -79,7 +82,7 @@ struct Canvas::Impl
         //Update single paint node
         if (paint) {
             paint->pImpl->update(*renderer, nullptr, compList, RenderUpdateFlag::None);
-        //Update retained all paint nodes
+        //Update all retained paint nodes
         } else {
             for (auto paint: paints) {
                 paint->pImpl->update(*renderer, nullptr, compList, RenderUpdateFlag::None);

src/lib/tvgPaint.h

@@ -123,7 +123,7 @@ namespace tvg
 
         bool dispose(RenderMethod& renderer)
         {
-            if (this->compTarget) this->compTarget->pImpl->dispose(renderer);
+            if (compTarget) compTarget->pImpl->dispose(renderer);
             return smethod->dispose(renderer);
         }