LibGfx+PixelPaint: Add Point::end_point_for_aspect_ratio method

Previously we only had `Point::end_point_for_square_aspect_ratio`,
which was convenient for PixelPaint but assumed the aspect ratio
was always fixed at 1. This patch replaces it with a new mthod that
takes in an arbitrary aspect ratio and computes the end point based
off that.

There's some explicit casting going on in `Point.cpp` to ensure that
the types line up, since we're templating Point based on `T`.`

Author: mustafaquraish

Userland/Applications/PixelPaint/EllipseTool.cpp

@@ -90,7 +90,7 @@ void EllipseTool::on_mousemove(Layer*, MouseEvent& event)
     m_draw_mode = event.layer_event().alt() ? DrawMode::FromCenter : DrawMode::FromCorner;
 
     if (event.layer_event().shift())
-        m_ellipse_end_position = m_ellipse_start_position.end_point_for_square_aspect_ratio(event.layer_event().position());
+        m_ellipse_end_position = m_ellipse_start_position.end_point_for_aspect_ratio(event.layer_event().position(), 1.0);
     else
         m_ellipse_end_position = event.layer_event().position();
 

Userland/Applications/PixelPaint/RectangleTool.cpp

@@ -96,7 +96,7 @@ void RectangleTool::on_mousemove(Layer* layer, MouseEvent& event)
     m_draw_mode = event.layer_event().alt() ? DrawMode::FromCenter : DrawMode::FromCorner;
 
     if (event.layer_event().shift())
-        m_rectangle_end_position = m_rectangle_start_position.end_point_for_square_aspect_ratio(event.layer_event().position());
+        m_rectangle_end_position = m_rectangle_start_position.end_point_for_aspect_ratio(event.layer_event().position(), 1.0);
     else
         m_rectangle_end_position = event.layer_event().position();
 

Userland/Libraries/LibGfx/Point.cpp

@@ -20,14 +20,19 @@ void Point<T>::constrain(Rect<T> const& rect)
 }
 
 template<typename T>
-[[nodiscard]] Point<T> Point<T>::end_point_for_square_aspect_ratio(Point<T> const& previous_end_point) const
+[[nodiscard]] Point<T> Point<T>::end_point_for_aspect_ratio(Point<T> const& previous_end_point, float aspect_ratio) const
 {
-    const T dx = previous_end_point.x() - x();
-    const T dy = previous_end_point.y() - y();
-    const T x_sign = dx >= 0 ? 1 : -1;
-    const T y_sign = dy >= 0 ? 1 : -1;
-    const T abs_size = AK::max(AK::abs(dx), AK::abs(dy));
-    return { x() + x_sign * abs_size, y() + y_sign * abs_size };
+    VERIFY(aspect_ratio > 0);
+    const T x_sign = previous_end_point.x() >= x() ? 1 : -1;
+    const T y_sign = previous_end_point.y() >= y() ? 1 : -1;
+    T dx = AK::abs(previous_end_point.x() - x());
+    T dy = AK::abs(previous_end_point.y() - y());
+    if (dx > dy) {
+        dy = (T)((float)dx / aspect_ratio);
+    } else {
+        dx = (T)((float)dy * aspect_ratio);
+    }
+    return { x() + x_sign * dx, y() + y_sign * dy };
 }
 
 template<>

Userland/Libraries/LibGfx/Point.h

@@ -231,7 +231,7 @@ class Point {
         return { AK::abs(dx_relative_to(other)), AK::abs(dy_relative_to(other)) };
     }
 
-    [[nodiscard]] Point end_point_for_square_aspect_ratio(Point const&) const;
+    [[nodiscard]] Point end_point_for_aspect_ratio(Point const& previous_end_point, float aspect_ratio) const;
 
     template<typename U>
     [[nodiscard]] Point<U> to_type() const