Drawing Canvas & Text Rendering

Drawing shapes and rendering text onto frames is useful for displaying visualization boxes, showing tracking overlays, and labeling image outputs.

Basic Geometric Shapes

All drawing functions operate directly on the Image struct (manipulating internal pixel bytes on the CPU and returning the modified frame).

Lines

Draws a straight line from p1 to p2 with a specified Scalar color.

let p1 = Point::new(10, 10);
let p2 = Point::new(390, 10);
let color = Scalar::new(1.0, 0.0, 0.0, 0.0); // Red
let image = image.draw_line(p1, p2, color)?;

Rectangles

Draws a rectangle with the specified borders or fills it.

let rect = Rect::new(50, 50, 100, 100);
let color = Scalar::new(0.0, 1.0, 0.0, 0.0); // Green
// Draw with thickness = 2
let image = image.draw_rectangle(rect, color, 2)?;

// Draw a filled rectangle with thickness = -1
let image = image.draw_rectangle(rect, color, -1)?;

Circles

Draws a circle around a center point with a given radius.

let center = Point::new(200, 150);
let radius = 40;
let color = Scalar::new(0.0, 0.0, 1.0, 0.0); // Blue
// Draw a filled circle
let image = image.draw_circle(center, radius, color, -1)?;

Ellipses

Draws an ellipse with configurable rotation and angle range.

let center = Point::new(300, 200);
let axes = (50, 30); // semi-major, semi-minor
let color = Scalar::new(1.0, 1.0, 0.0, 0.0); // Yellow
// Draw a filled ellipse
let image = image.draw_ellipse(center, axes, 30.0, 0.0, 360.0, color, -1)?;

Polygons & Arrows

Polyline

Draws connected line segments.

let points = vec![
    Point::new(10, 10),
    Point::new(50, 10),
    Point::new(50, 50),
    Point::new(10, 50),
    Point::new(10, 10),
];
let image = image.draw_polyline(&points, Scalar::all(1.0), 1)?;

Filled Polygon

Fills a closed polygon region using scanline fill.

let points = vec![
    Point::new(100, 100),
    Point::new(200, 100),
    Point::new(150, 150),
];
let image = image.fill_poly(&points, Scalar::all(0.5))?;

Arrowed Line

Draws a line with an arrowhead.

let image = image.draw_arrowed_line(
    Point::new(10, 10),
    Point::new(100, 80),
    Scalar::all(1.0),
    1,
    0.3, // tip_length ratio
)?;

Markers

Draws a marker symbol at a point.

let image = image.draw_marker(Point::new(50, 50), Scalar::all(1.0), MarkerType::Cross, 10)?;
let image = image.draw_marker(Point::new(50, 50), Scalar::all(1.0), MarkerType::Circle, 10)?;
let image = image.draw_marker(Point::new(50, 50), Scalar::all(1.0), MarkerType::Diamond, 10)?;

Available marker types: Cross, TiltedCross, Diamond, Square, Circle, Filled.

Rendering Text

Iris contains a lightweight, built-in 5x7 bitmap font (FONT_5X7) to render standard ASCII labels onto images directly, eliminating the need to link external system font files.

let org = Point::new(50, 250);
let scale = 2;
let color = Scalar::all(1.0); // White text
let image = image.draw_text("Iris library", org, scale, color)?;