LibGUI+PixelPaint: Move fit_image_to_view to AbstractZoomPanWidget

We often want to zoom and fit the content of the widget into the
visible frame (or some rect within the frame), and it makes sense to
move this functionality into the AbstractZoomPanWidget to minimize
the amount of coordinate math derived classes need to do.

This commit moves the code that implements this functionality from
`PixelPaint::ImageEditor` into `AbstractZoomPanWidget` so that we
can also use it for other applications (such as ImageViewer!)

Userland/Applications/PixelPaint/ImageEditor.cpp

@@ -529,28 +529,7 @@ void ImageEditor::fit_image_to_view(FitType type)
         };
     }
 
-    const float border_ratio = 0.95f;
-    auto image_size = image().size();
-    auto height_ratio = floorf(border_ratio * viewport_rect.height()) / (float)image_size.height();
-    auto width_ratio = floorf(border_ratio * viewport_rect.width()) / (float)image_size.width();
-
-    float new_scale = 1.0f;
-    switch (type) {
-    case FitType::Width:
-        new_scale = width_ratio;
-        break;
-    case FitType::Height:
-        new_scale = height_ratio;
-        break;
-    case FitType::Image:
-        new_scale = min(height_ratio, width_ratio);
-        break;
-    }
-
-    float offset = m_show_rulers ? -m_ruler_thickness / (scale() * 2.0f) : 0.0f;
-
-    set_origin(Gfx::FloatPoint(offset, offset));
-    set_scale(new_scale);
+    fit_content_to_rect(viewport_rect, type);
 }
 
 void ImageEditor::image_did_change(Gfx::IntRect const& modified_image_rect)

Userland/Applications/PixelPaint/ImageEditor.h

@@ -63,13 +63,7 @@ public:
 
     Layer* layer_at_editor_position(Gfx::IntPoint const&);
 
-    enum class FitType {
-        Width,
-        Height,
-        Image
-    };
-
-    void fit_image_to_view(FitType type = FitType::Image);
+    void fit_image_to_view(FitType type = FitType::Both);
 
     Color primary_color() const { return m_primary_color; }
     void set_primary_color(Color);

Userland/Applications/PixelPaint/MainWidget.cpp

@@ -658,7 +658,7 @@ void MainWidget::initialize_menubar(GUI::Window& window)
                 editor->fit_image_to_view(ImageEditor::FitType::Height);
                 return;
             case s_zoom_level_fit_image:
-                editor->fit_image_to_view(ImageEditor::FitType::Image);
+                editor->fit_image_to_view(ImageEditor::FitType::Both);
                 return;
             }
         }

Userland/Libraries/LibGUI/AbstractZoomPanWidget.cpp

@@ -180,4 +180,29 @@ void AbstractZoomPanWidget::set_scale_bounds(float min_scale, float max_scale)
     m_max_scale = max_scale;
 }
 
+void AbstractZoomPanWidget::fit_content_to_rect(Gfx::IntRect const& viewport_rect, FitType type)
+{
+    const float border_ratio = 0.95f;
+    auto image_size = m_original_rect.size();
+    auto height_ratio = floorf(border_ratio * viewport_rect.height()) / (float)image_size.height();
+    auto width_ratio = floorf(border_ratio * viewport_rect.width()) / (float)image_size.width();
+
+    float new_scale = 1.0f;
+    switch (type) {
+    case FitType::Width:
+        new_scale = width_ratio;
+        break;
+    case FitType::Height:
+        new_scale = height_ratio;
+        break;
+    case FitType::Both:
+        new_scale = min(height_ratio, width_ratio);
+        break;
+    }
+
+    auto const& offset = rect().center() - viewport_rect.center();
+    set_origin(Gfx::FloatPoint(offset.x(), offset.y()));
+    set_scale(new_scale);
+}
+
 }

Userland/Libraries/LibGUI/AbstractZoomPanWidget.h

@@ -54,6 +54,17 @@ public:
 
     Function<void(float)> on_scale_change;
 
+    enum class FitType {
+        Width,
+        Height,
+        Both
+    };
+    void fit_content_to_rect(Gfx::IntRect const& rect, FitType = FitType::Both);
+    void fit_content_to_view(FitType fit_type = FitType::Both)
+    {
+        fit_content_to_rect(rect(), fit_type);
+    }
+
 private:
     Gfx::IntRect m_original_rect;
     Gfx::IntRect m_content_rect;