LibDraw: Add GraphicsBitmap::to_shareable_bitmap()

This function returns the bitmap itself if it's already backed by a
SharedBuffer object, otherwise it creates a shareable copy of itself
and returns that.

Libraries/LibDraw/GraphicsBitmap.cpp

@@ -77,6 +77,16 @@ GraphicsBitmap::GraphicsBitmap(Format format, NonnullRefPtr<SharedBuffer>&& shar
     ASSERT(format != Format::Indexed8);
 }
 
+NonnullRefPtr<GraphicsBitmap> GraphicsBitmap::to_shareable_bitmap() const
+{
+    if (m_shared_buffer)
+        return *this;
+    auto buffer = SharedBuffer::create_with_size(size_in_bytes());
+    auto bitmap = GraphicsBitmap::create_with_shared_buffer(m_format, *buffer, m_size);
+    memcpy(buffer->data(), scanline(0), size_in_bytes());
+    return bitmap;
+}
+
 GraphicsBitmap::~GraphicsBitmap()
 {
     if (m_needs_munmap) {

Libraries/LibDraw/GraphicsBitmap.h

@@ -3,10 +3,10 @@
 #include "Color.h"
 #include "Rect.h"
 #include "Size.h"
-#include <AK/String.h>
 #include <AK/MappedFile.h>
 #include <AK/RefCounted.h>
 #include <AK/RefPtr.h>
+#include <AK/String.h>
 #include <AK/StringView.h>
 #include <SharedBuffer.h>
 
@@ -24,6 +24,9 @@ public:
     static RefPtr<GraphicsBitmap> load_from_file(const StringView& path);
     static RefPtr<GraphicsBitmap> load_from_file(Format, const StringView& path, const Size&);
     static NonnullRefPtr<GraphicsBitmap> create_with_shared_buffer(Format, NonnullRefPtr<SharedBuffer>&&, const Size&);
+
+    NonnullRefPtr<GraphicsBitmap> to_shareable_bitmap() const;
+
     ~GraphicsBitmap();
 
     RGBA32* scanline(int y);
@@ -39,6 +42,9 @@ public:
     size_t pitch() const { return m_pitch; }
     int shared_buffer_id() const { return m_shared_buffer ? m_shared_buffer->shared_buffer_id() : -1; }
 
+    SharedBuffer* shared_buffer() { return m_shared_buffer.ptr(); }
+    const SharedBuffer* shared_buffer() const { return m_shared_buffer.ptr(); }
+
     unsigned bpp() const
     {
         switch (m_format) {
@@ -157,7 +163,7 @@ inline Color GraphicsBitmap::get_pixel(int x, int y) const
         return get_pixel<Format::Indexed8>(x, y);
     default:
         ASSERT_NOT_REACHED();
-        return { };
+        return {};
     }
 }