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Scale a circle to make an ellipse instead of Bezier curves #121

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Mar 11, 2024
Merged

Scale a circle to make an ellipse instead of Bezier curves #121

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27 changes: 12 additions & 15 deletions lib/render.ml
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Original file line number Diff line number Diff line change
Expand Up @@ -16,13 +16,6 @@ let draw_circle ctx ({ c; radius; stroke; fill } : circle) =
Option.iter fill_circle fill;
Cairo.Path.clear ctx.ctx

let create_control_points ({ x; y }, rx, ry) =
let width_two_thirds = rx *. (2. /. 3.) *. 2. in
( { x; y = y -. ry },
(x +. width_two_thirds, y -. ry, x +. width_two_thirds, y +. ry, x, y +. ry),
(x -. width_two_thirds, y +. ry, x -. width_two_thirds, y -. ry, x, y -. ry)
)

let draw_ellipse ctx { c; rx; ry; stroke; fill } =
let stroke_ellipse stroke =
set_color stroke;
Expand All @@ -32,14 +25,18 @@ let draw_ellipse ctx { c; rx; ry; stroke; fill } =
set_color fill;
Cairo.fill_preserve ctx.ctx
in
let start, curve_one, curve_two =
create_control_points (c, rx, Float.neg ry)
in
Cairo.move_to ctx.ctx start.x start.y;
let x1, y1, x2, y2, x3, y3 = curve_one in
Cairo.curve_to ctx.ctx x1 y1 x2 y2 x3 y3;
let x1, y1, x2, y2, x3, y3 = curve_two in
Cairo.curve_to ctx.ctx x1 y1 x2 y2 x3 y3;

(* Save the current transformation matrix *)
let save_matrix = Cairo.get_matrix ctx.ctx in

(* Translate and scale to create an ellipse from a circle *)
Cairo.translate ctx.ctx c.x (Float.neg c.y);
Cairo.scale ctx.ctx rx ry;
Cairo.arc ctx.ctx 0. 0. ~r:1. ~a1:0. ~a2:(2. *. Float.pi);

(* Restore the original transformation matrix *)
Cairo.set_matrix ctx.ctx save_matrix;

Option.iter stroke_ellipse stroke;
Option.iter fill_ellipse fill;
Cairo.Path.clear ctx.ctx
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