PixelPaint: Add `Fit Image To View` action

This is a feature I missed from Photoshop: it sets the scale and
position so that the image fits (it's longest dimension) into
the editor view. There's a 5% border left around the image to
provide context. This is just arbitrary seemed like the right
amount after some trial and error.

Userland/Applications/PixelPaint/ImageEditor.cpp

@@ -425,6 +425,18 @@ void ImageEditor::scale_by(float scale_delta)
     }
 }
 
+void ImageEditor::fit_image_to_view()
+{
+    const float border_ratio = 0.95f;
+    auto image_size = image().size();
+    auto height_ratio = rect().height() / (float)image_size.height();
+    auto width_ratio = rect().width() / (float)image_size.width();
+    m_scale = border_ratio * min(height_ratio, width_ratio);
+
+    m_pan_origin = Gfx::FloatPoint(0, 0);
+    relayout();
+}
+
 void ImageEditor::reset_scale_and_position()
 {
     if (m_scale != 1.0f)

Userland/Applications/PixelPaint/ImageEditor.h

@@ -52,6 +52,7 @@ public:
 
     float scale() const { return m_scale; }
     void scale_centered_on_position(Gfx::IntPoint const&, float);
+    void fit_image_to_view();
     void reset_scale_and_position();
     void scale_by(float);
 

Userland/Applications/PixelPaint/MainWidget.cpp

@@ -342,6 +342,11 @@ void MainWidget::initialize_menubar(GUI::Window& window)
     view_menu.add_action(*m_zoom_in_action);
     view_menu.add_action(*m_zoom_out_action);
     view_menu.add_action(*m_reset_zoom_action);
+    view_menu.add_action(GUI::Action::create(
+        "&Fit Image To View", [&](auto&) {
+            if (auto* editor = current_image_editor())
+                editor->fit_image_to_view();
+        }));
     view_menu.add_separator();
     view_menu.add_action(*m_add_guide_action);
     view_menu.add_action(*m_show_guides_action);