LibGfx: Use common class template for PBM/PGM/PPM image loaders

PBM, PGM, and PPM image loaders are mostly common. The only difference
is how the data is read and the associated magic numbers. The magic
numbers are already made common using the loading contexts. Now make
the implementations common via a class template which accepts the
context to disambiguate.

Userland/Libraries/LibGfx/PortableImageMapLoader.h

@@ -11,6 +11,7 @@
 #include <AK/StringView.h>
 #include <AK/Types.h>
 #include <LibGfx/Bitmap.h>
+#include <LibGfx/PortableImageLoaderCommon.h>
 
 namespace Gfx {
 
@@ -45,4 +46,117 @@ struct PortableImageMapLoadingContext {
     RefPtr<Gfx::Bitmap> bitmap;
 };
 
+template<typename TContext>
+class PortableImageDecoderPlugin final : public ImageDecoderPlugin {
+public:
+    PortableImageDecoderPlugin(const u8*, size_t);
+    virtual ~PortableImageDecoderPlugin() override = default;
+
+    virtual IntSize size() override;
+
+    virtual void set_volatile() override;
+    [[nodiscard]] virtual bool set_nonvolatile(bool& was_purged) override;
+
+    virtual bool sniff() override;
+
+    virtual bool is_animated() override;
+    virtual size_t loop_count() override;
+    virtual size_t frame_count() override;
+    virtual ErrorOr<ImageFrameDescriptor> frame(size_t index) override;
+
+private:
+    OwnPtr<TContext> m_context;
+};
+
+template<typename TContext>
+PortableImageDecoderPlugin<TContext>::PortableImageDecoderPlugin(const u8* data, size_t size)
+{
+    m_context = make<TContext>();
+    m_context->data = data;
+    m_context->data_size = size;
+}
+
+template<typename TContext>
+IntSize PortableImageDecoderPlugin<TContext>::size()
+{
+    if (m_context->state == TContext::State::Error)
+        return {};
+
+    if (m_context->state < TContext::State::Decoded) {
+        bool success = decode(*m_context);
+        if (!success)
+            return {};
+    }
+
+    return { m_context->width, m_context->height };
+}
+
+template<typename TContext>
+void PortableImageDecoderPlugin<TContext>::set_volatile()
+{
+    if (m_context->bitmap)
+        m_context->bitmap->set_volatile();
+}
+
+template<typename TContext>
+bool PortableImageDecoderPlugin<TContext>::set_nonvolatile(bool& was_purged)
+{
+    if (!m_context->bitmap)
+        return false;
+
+    return m_context->bitmap->set_nonvolatile(was_purged);
+}
+
+template<typename TContext>
+bool PortableImageDecoderPlugin<TContext>::sniff()
+{
+    using Context = TContext;
+    if (m_context->data_size < 2)
+        return false;
+
+    if (m_context->data[0] == 'P' && m_context->data[1] == Context::FormatDetails::ascii_magic_number)
+        return true;
+
+    if (m_context->data[0] == 'P' && m_context->data[1] == Context::FormatDetails::binary_magic_number)
+        return true;
+
+    return false;
+}
+
+template<typename TContext>
+bool PortableImageDecoderPlugin<TContext>::is_animated()
+{
+    return false;
+}
+
+template<typename TContext>
+size_t PortableImageDecoderPlugin<TContext>::loop_count()
+{
+    return 0;
+}
+
+template<typename TContext>
+size_t PortableImageDecoderPlugin<TContext>::frame_count()
+{
+    return 1;
+}
+
+template<typename TContext>
+ErrorOr<ImageFrameDescriptor> PortableImageDecoderPlugin<TContext>::frame(size_t index)
+{
+    if (index > 0)
+        return Error::from_string_literal("PortableImageDecoderPlugin: Invalid frame index"sv);
+
+    if (m_context->state == TContext::State::Error)
+        return Error::from_string_literal("PortableImageDecoderPlugin: Decoding failed"sv);
+
+    if (m_context->state < TContext::State::Decoded) {
+        bool success = decode(*m_context);
+        if (!success)
+            return Error::from_string_literal("PortableImageDecoderPlugin: Decoding failed"sv);
+    }
+
+    VERIFY(m_context->bitmap);
+    return ImageFrameDescriptor { m_context->bitmap, 0 };
+}
 }