FileManager: Add basic thumbnailing of PNG images.

These use nearest neighbor and are computed synchronously on directory load
so it's neither fast nor very beautiful. These issues both need work on
other parts of the system to fix.

Applications/FileManager/DirectoryModel.cpp

@@ -6,6 +6,8 @@
 #include <pwd.h>
 #include <AK/FileSystemPath.h>
 #include <AK/StringBuilder.h>
+#include <SharedGraphics/GraphicsBitmap.h>
+#include <SharedGraphics/Painter.h>
 
 DirectoryModel::DirectoryModel()
 {
@@ -79,8 +81,18 @@ const GraphicsBitmap& DirectoryModel::icon_for(const Entry& entry) const
         return *m_socket_icon;
     if (entry.mode & S_IXUSR)
         return *m_executable_icon;
-    if (entry.name.ends_with(".png"))
-        return *m_filetype_image_icon;
+    if (entry.name.ends_with(".png")) {
+        if (!entry.thumbnail) {
+            if (auto png_bitmap = GraphicsBitmap::load_from_file(entry.full_path(*this))) {
+                entry.thumbnail = GraphicsBitmap::create(png_bitmap->format(), { 32, 32 });
+                Painter painter(*entry.thumbnail);
+                painter.draw_scaled_bitmap(entry.thumbnail->rect(), *png_bitmap, png_bitmap->rect());
+            }
+        }
+        if (!entry.thumbnail)
+            return *m_filetype_image_icon;
+        return *entry.thumbnail;
+    }
     return *m_file_icon;
 }
 

Applications/FileManager/DirectoryModel.h

@@ -45,8 +45,10 @@ private:
         uid_t uid { 0 };
         uid_t gid { 0 };
         ino_t inode { 0 };
+        mutable RetainPtr<GraphicsBitmap> thumbnail;
         bool is_directory() const { return S_ISDIR(mode); }
         bool is_executable() const { return mode & S_IXUSR; }
+        String full_path(const DirectoryModel& model) const { return String::format("%s/%s", model.path().characters(), name.characters()); }
     };
 
     const Entry& entry(int index) const

SharedGraphics/GraphicsBitmap.h

@@ -30,6 +30,7 @@ public:
     int shared_buffer_id() const { return m_shared_buffer ? m_shared_buffer->shared_buffer_id() : -1; }
 
     bool has_alpha_channel() const { return m_format == Format::RGBA32; }
+    Format format() const { return m_format; }
 
 private:
     GraphicsBitmap(Format, const Size&);