LibGfx: Re-structure the whole initialization pattern for image decoders

When trying to figure out the correct implementation, we now have a very
strong distinction on plugins that are well suited for sniffing, and
plugins that need a MIME type to be chosen.

Instead of having multiple calls to non-static virtual sniff methods for
each Image decoding plugin, we have 2 static methods for each
implementation:
1. The sniff method, which in contrast to the old method, gets a
    ReadonlyBytes parameter and ensures we can figure out the result
    with zero heap allocations for most implementations.
2. The create method, which just creates a new instance so we don't
    expose the constructor to everyone anymore.

In addition to that, we have a new virtual method called initialize,
which has a per-implementation initialization pattern to actually ensure
each implementation can construct a decoder object, and then have a
correct context being applied to it for the actual decoding.

1 files changed, 6 insertions, 2 deletions

diff --git a/Userland/Libraries/LibGfx/QOILoader.h b/Userland/Libraries/LibGfx/QOILoader.h
index 9446e69a16..b5df791830 100644
--- a/Userland/Libraries/LibGfx/QOILoader.h
+++ b/Userland/Libraries/LibGfx/QOILoader.h
@@ -40,13 +40,15 @@ struct QOILoadingContext {
 
 class QOIImageDecoderPlugin final : public ImageDecoderPlugin {
 public:
+    static ErrorOr<bool> sniff(ReadonlyBytes);
+    static ErrorOr<NonnullOwnPtr<ImageDecoderPlugin>> create(ReadonlyBytes);
+
     virtual ~QOIImageDecoderPlugin() override = default;
-    QOIImageDecoderPlugin(u8 const*, size_t);
 
     virtual IntSize size() override;
     virtual void set_volatile() override;
     [[nodiscard]] virtual bool set_nonvolatile(bool& was_purged) override;
-    virtual bool sniff() override;
+    virtual bool initialize() override;
     virtual bool is_animated() override { return false; }
     virtual size_t loop_count() override { return 0; }
     virtual size_t frame_count() override { return 1; }
@@ -56,6 +58,8 @@ private:
     ErrorOr<void> decode_header_and_update_context(InputMemoryStream&);
     ErrorOr<void> decode_image_and_update_context(InputMemoryStream&);
 
+    QOIImageDecoderPlugin(u8 const*, size_t);
+
     OwnPtr<QOILoadingContext> m_context;
 };