[core] add clone() call to Image objects

include/mbgl/util/image.hpp

@@ -48,6 +48,13 @@ public:
         return size && data.get() != nullptr;
     }
 
+    template <typename T = Image>
+    T clone() const {
+        T copy(size);
+        std::copy(data.get(), data.get() + bytes(), copy.data.get());
+        return copy;
+    }
+
     size_t stride() const { return channels * size.width; }
     size_t bytes() const { return stride() * size.height; }
 

platform/default/png_writer.cpp

@@ -39,12 +39,8 @@ namespace mbgl {
 
 // Encode PNGs without libpng.
 std::string encodePNG(const PremultipliedImage& pre) {
-    const UnassociatedImage src = [&pre] {
-        // Make copy of the image so that we can unpremultiply it.
-        PremultipliedImage copy(pre.size);
-        std::copy(pre.data.get(), pre.data.get() + pre.bytes(), copy.data.get());
-        return util::unpremultiply(std::move(copy));
-    }();
+    // Make copy of the image so that we can unpremultiply it.
+    const auto src = util::unpremultiply(pre.clone());
 
     // PNG magic bytes
     const char preamble[8] = { char(0x89), 'P', 'N', 'G', '\r', '\n', 0x1a, '\n' };