indexing

	description: "[

		A circle (approximated by a polygon).

	]"
	date: "$Date$"
	revision: "$Revision$"

class EM_CIRCLE

inherit

	EM_CLOSED_FIGURE
		redefine
			width, height, set_x_y, update_bounding_box,
			publish_mouse_event
		end

	DOUBLE_MATH
		export
			{NONE} all
		undefine
			is_equal,
			copy,
			default_create
		end

create

	make, make_inside_box, make_through_three_points

feature -- Initialization

	default_number_of_polygon_points: INTEGER is 60

	default_max_number_of_polygon_points: INTEGER is 256

	make (a_center: EM_VECTOR_2D; a_radius: DOUBLE) is
			-- Make circle with `a_center' and `a_radius'.
		require
			a_center_not_void: a_center /= Void
			a_radius_is_positiive: a_radius > 0
		do
			default_create
			center := a_center
			radius := a_radius
			set_visible (True)
			number_of_polygon_points := default_number_of_polygon_points
			max_number_of_polygon_points := default_max_number_of_polygon_points
			build_approximating_polygon
			update_bounding_box
		ensure
			is_visible: is_visible
		end

	make_inside_box (a_box: EM_RECTANGLE) is
			-- Make largest circle fitting into `a_box'
			-- with `center' at center of `a_box'.
		do
			make (a_box.center, a_box.width.min (a_box.height) / 2)
		ensure
			is_visible: is_visible
		end

	make_through_three_points (a_vector, b_vector, c_vector: EM_VECTOR_2D) is
			-- creates a circle, that goes through the 3 given points
			-- if the 3 points are all aligned no such circle can be found and the unit circle is created
			-- in that case the variable `not_created' will be set, to inform the client
		require
			a_vector_not_void: a_vector /= Void
			b_vector_not_void: b_vector /= Void
			c_vector_not_void: c_vector /= Void
		local
			z1, z2, z3, dividor: EM_COMPLEX
		do
			create z1.make (a_vector.x, a_vector.y)
			create z2.make (b_vector.x, b_vector.y)
			create z3.make (c_vector.x, c_vector.y)

			dividor := z1 * (z3-z2).conjugated + z2 * (z1-z3).conjugated + z3 * (z2-z1).conjugated

			if dividor.real /= 0 or dividor.imaginary /= 0 then
				z1 := ((z2-z3).times (z1.abs_squared) + (z3-z1).times (z2.abs_squared) + (z1-z2).times (z3.abs_squared)) / dividor
				make (create {EM_VECTOR_2D}.make (z1.real, z1.imaginary), z1.to_vector_2d.distance (a_vector))
			else
				-- the 3 points are all in one line. No such circle exists
				make (create {EM_VECTOR_2D}.make (0,0), 1)
				not_created := True
			end
		ensure
			is_visible: is_visible
		end

feature -- Status report

	width: INTEGER is
			-- Width of `Current'.
		do
			Result := (center.x + radius).ceiling - x
		end

	height: INTEGER is
			-- Height of `Current'.
		do
			Result := (center.y + radius).ceiling - y
		end

	radius: DOUBLE
			-- Radius of `Current' circle.

	center: EM_VECTOR_2D
			-- Center of `Current' circle.

	number_of_polygon_points: INTEGER
			-- Number of polygon points used to approximate `Current' circle
			-- when not `is_approximated_adaptively'.

	max_number_of_polygon_points: INTEGER
			-- Maximum number of polygon points used to approximate `Current' circle
			-- when `is_approximated_adaptively'.

	min_number_of_polygon_points: INTEGER is 8
			-- Minimum number of points used to approximate a circle.

	is_approximated_adaptively: BOOLEAN
			-- Is `Current' drawed with an adaptively choosen number of polygon points
			-- depending on `display_resolution' of surface it is drawed onto?

	not_created: BOOLEAN
			-- will be set to true, if the circle could not be created correctly (in case of 3 aligned points in `make_through_three_points')

feature -- Status setting

	enable_adaptive_approximation is
			-- Enable drawing `Current' with an adaptively choosen number of polygon points,
			-- depending on `radius' and surface's `display_resolution'.
		do
			is_approximated_adaptively := True
		end

	disable_adaptive_approximation is
			-- Disable drawing `Current' with an adaptively choosen number of polygon points,
			-- depending on `radius' and surface's `display_resolution'.
		do
			is_approximated_adaptively := False
		end

	set_center (a_center: EM_VECTOR_2D) is
			-- Set `center' to `a_center'.
		do
			center := a_center
			build_approximating_polygon
			update_bounding_box
		end

	set_radius (a_radius: DOUBLE) is
			-- Set `radius' to `a_radius'.
		do
			radius := a_radius
			x := (center.x - radius).floor
			y := (center.y - radius).floor
			build_approximating_polygon
			update_bounding_box
		end

	set_number_of_polygon_points (a_count: INTEGER) is
			-- Set `number_of_polygon_points' to `a_count'.
		require
			a_count_big_enough: a_count >= min_number_of_polygon_points
		do
			number_of_polygon_points := a_count
			build_approximating_polygon
		ensure
			number_of_polygon_points_set: number_of_polygon_points = a_count
		end

	set_max_number_of_polygon_points (a_count: INTEGER) is
			-- Set `max_number_of_polygon_points' to `a_count'.
		require
			a_count_big_enough: a_count >= min_number_of_polygon_points
		do
			max_number_of_polygon_points := a_count
		ensure
			max_number_of_polygon_points_set: max_number_of_polygon_points = a_count
		end

	set_x_y (x_position: INTEGER; y_position: INTEGER) is
			-- Set `x' and `y' to `x_position' and `y_position'.
		local
			diff: EM_VECTOR_2D
		do
			create diff.make (x_position - x, y_position - y)
			center.move_by (diff)
			y := y_position
			x := x_position
			build_approximating_polygon
		end

	update_bounding_box is
			-- Recalculate `bounding_box' (`x', `y', `width', `height')
			-- to surround `Current'.
		do
			x := (center.x - (line_width / 2) - radius).floor
			y := (center.y - (line_width / 2) - radius).floor
			internal_width := (center.x + (line_width / 2) + radius).ceiling - x
			internal_height := (center.y + (line_width / 2) + radius).ceiling - y
		end

feature -- Drawing

	draw (drawing_interface: EM_SURFACE) is
			-- Draw `Current' using `drawing_interface'.
		do
			if is_visible then
				if is_approximated_adaptively then
					number_of_polygon_points := (drawing_interface.device_resolution * radius).floor.max (min_number_of_polygon_points). min(max_number_of_polygon_points)
					if (number_of_polygon_points - approximating_polygon.count).abs / number_of_polygon_points > 0.25 then
						build_approximating_polygon
					end
				end
				approximating_polygon.set_fill_color (fill_color)
				approximating_polygon.set_line_color (line_color)
				approximating_polygon.set_line_width (line_width)
				approximating_polygon.set_filled (is_filled)
				drawing_interface.draw_object (approximating_polygon)
			end
		end

feature -- Mouse Events

	publish_mouse_event (a_mouse_event: EM_MOUSE_EVENT) is
			-- Publish mouse event when `a_mouse_event' occured on `Current'.
			-- Only publish mouse event, if `proportional_point' lies inside circle.
		local
			dist, half_line_width: DOUBLE
		do
			dist := a_mouse_event.proportional_position.distance (center)
			half_line_width := line_width / 2
			if dist < radius + half_line_width then
				if is_filled or else dist > radius - half_line_width then
					dispatch_mouse_event (a_mouse_event)
					a_mouse_event.set_caught (True)
				end
			end
		end

feature {NONE} -- Implementation

	approximating_polygon: EM_POLYGON
			-- Polygon used to approximate `Current' when drawing it.

	build_approximating_polygon is
			-- Create polygon points for approximating `Current' circle
			-- with `number_of_points'.
		local
			p1, p2: EM_VECTOR_2D
		do
			create p1.make (0, radius)
			p2 := p1.rotation_around_zero (2 * Pi / number_of_polygon_points)
			create approximating_polygon.make_regular (number_of_polygon_points, center + p1, p2 - p1)
			points := approximating_polygon
		end

end