core: refactor renderable size ownership (#4512)

test/renderer/renderable.test.cpp

@@ -0,0 +1,23 @@
+#include <mln/test/util.hpp>
+
+#include <mln/gfx/renderable.hpp>
+
+namespace {
+
+class TestRenderable final : public mln::gfx::Renderable {
+public:
+    explicit TestRenderable(mln::Size size_)
+        : Renderable(size_, nullptr) {}
+
+    void resize(const mln::Size& size_) { setRenderableSize(size_); }
+};
+
+} // namespace
+
+TEST(Renderable, MaintainsCanonicalPhysicalSize) {
+    TestRenderable renderable({256, 128});
+    EXPECT_EQ(renderable.getSize(), (mln::Size{256, 128}));
+
+    renderable.resize({512, 384});
+    EXPECT_EQ(renderable.getSize(), (mln::Size{512, 384}));
+}