Mojo function 🡭

draw_ellipse_aa

fn def draw_ellipse_aa(mut canvas: Canvas, cx: Int, cy: Int, rx: Int, ry: Int, color: Color, supersample: Int = Int(4), width: Float64 = 1)

Anti-aliased ellipse outline, width pixels wide (default 1) – draw_circle_aa’s generalization to independent x/y radii.

Args:

• canvas (Canvas): Canvas to draw into.
• cx (Int): Center x.
• cy (Int): Center y.
• rx (Int): Horizontal radius in pixels, to the middle of the stroke.
• ry (Int): Vertical radius in pixels, to the middle of the stroke.
• color (Color): Outline color.
• supersample (Int): Sub-pixel grid side length per pixel (N -> N*N samples).
• width (Float64): Stroke width in pixels.

fn def draw_ellipse_aa(mut canvas: Canvas, cx: Float64, cy: Float64, rx: Float64, ry: Float64, color: Color, supersample: Int = Int(4), width: Float64 = 1)

draw_ellipse_aa at a sub-pixel center and radii; the whole-pixel overload above converts and calls this.

No single distance value serves both boundaries here: an ellipse’s (rx-w/2, ry-w/2) and (rx+w/2, ry+w/2) rings are two different ellipses, where a circle’s are concentric offsets of one curve. Each sample is tested against both in their own normalized space:

(dx/outer_rx)^2 + (dy/outer_ry)^2 <  1   (strictly inside outer)
(dx/inner_rx)^2 + (dy/inner_ry)^2 >= 1   (on or outside inner)

Applying +/-w/2 to rx and ry independently, rather than offsetting along the ellipse’s normal, makes the ring’s width vary around the ellipse: exactly width at the four axis extremes, narrower elsewhere. A normal-offset ring would need the perimeter parameterization. A stroke wider than the shorter diameter leaves no hole and draws the filled ellipse.

Args:

• canvas (Canvas): Canvas to draw into.
• cx (Float64): Center x, sub-pixel.
• cy (Float64): Center y, sub-pixel.
• rx (Float64): Horizontal radius in pixels, to the middle of the stroke.
• ry (Float64): Vertical radius in pixels, to the middle of the stroke.
• color (Color): Outline color.
• supersample (Int): Sub-pixel grid side length per pixel (N -> N*N samples).
• width (Float64): Stroke width in pixels.