feat: editor shapes, geometry and history

src/editor/shape.rs

@@ -0,0 +1,395 @@
+//! Markup tools and the geometry both painters share: the canvas (egui)
+//! and the export (tiny-skia) draw the same primitives, in image pixels.
+
+pub type P = (f32, f32);
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Tool {
+    Arrow,
+    Rectangle,
+    Ellipse,
+    Line,
+    Pen,
+    Highlighter,
+}
+
+impl Tool {
+    pub const ALL: [Tool; 6] = [
+        Tool::Arrow,
+        Tool::Rectangle,
+        Tool::Ellipse,
+        Tool::Line,
+        Tool::Pen,
+        Tool::Highlighter,
+    ];
+
+    pub fn label(self) -> &'static str {
+        match self {
+            Tool::Arrow => "Arrow",
+            Tool::Rectangle => "Rectangle",
+            Tool::Ellipse => "Ellipse",
+            Tool::Line => "Line",
+            Tool::Pen => "Pen",
+            Tool::Highlighter => "Highlighter",
+        }
+    }
+
+    fn freehand(self) -> bool {
+        matches!(self, Tool::Pen | Tool::Highlighter)
+    }
+}
+
+/// The toolbar's colours; the first is the default.
+pub const PALETTE: [[u8; 3]; 7] = [
+    [0xff, 0x3b, 0x30],
+    [0xff, 0x95, 0x00],
+    [0xff, 0xcc, 0x00],
+    [0x34, 0xc7, 0x59],
+    [0x00, 0x7a, 0xff],
+    [0x00, 0x00, 0x00],
+    [0xff, 0xff, 0xff],
+];
+
+/// S, M, L in image pixels; M is the default.
+pub const WIDTHS: [(&str, f32); 3] = [("S", 2.0), ("M", 4.0), ("L", 8.0)];
+
+const HIGHLIGHT_ALPHA: u8 = 102;
+const CLICK: f32 = 2.0;
+const ELLIPSE_POINTS: usize = 72;
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub struct Style {
+    pub color: [u8; 3],
+    pub width: f32,
+}
+
+/// One finished mark. Two-point tools hold [start, end]; Pen and
+/// Highlighter hold every point.
+#[derive(Debug, Clone, PartialEq)]
+pub struct Shape {
+    pub tool: Tool,
+    pub style: Style,
+    pub points: Vec<P>,
+}
+
+impl Shape {
+    /// A press without a real drag. A Pen click still leaves a dot.
+    pub fn is_click(&self) -> bool {
+        if self.tool == Tool::Pen {
+            return false;
+        }
+        let first = self.points[0];
+        self.points
+            .iter()
+            .all(|p| (p.0 - first.0).hypot(p.1 - first.1) < CLICK)
+    }
+}
+
+/// A shape being drawn.
+#[derive(Debug, Clone)]
+pub struct Drag {
+    tool: Tool,
+    style: Style,
+    points: Vec<P>,
+}
+
+impl Drag {
+    pub fn new(tool: Tool, style: Style, start: P) -> Drag {
+        Drag {
+            tool,
+            style,
+            points: vec![start],
+        }
+    }
+
+    pub fn move_to(&mut self, p: P) {
+        if self.tool.freehand() || self.points.len() == 1 {
+            self.points.push(p);
+        } else {
+            self.points[1] = p;
+        }
+    }
+
+    /// The shape so far; `shift` applies the tool's constraint.
+    pub fn shape(&self, shift: bool) -> Shape {
+        let mut points = self.points.clone();
+        if !self.tool.freehand() && points.len() == 2 {
+            points[1] = constrain(self.tool, points[0], points[1], shift);
+        }
+        Shape {
+            tool: self.tool,
+            style: self.style,
+            points,
+        }
+    }
+}
+
+/// Shift: lines and arrows snap to 45° steps, rectangles and ellipses
+/// become squares and circles.
+pub fn constrain(tool: Tool, start: P, end: P, shift: bool) -> P {
+    if !shift {
+        return end;
+    }
+    let (dx, dy) = (end.0 - start.0, end.1 - start.1);
+    match tool {
+        Tool::Line | Tool::Arrow => {
+            let step = std::f32::consts::FRAC_PI_4;
+            let angle = (dy.atan2(dx) / step).round() * step;
+            let len = dx.hypot(dy);
+            (start.0 + len * angle.cos(), start.1 + len * angle.sin())
+        }
+        Tool::Rectangle | Tool::Ellipse => {
+            let side = dx.abs().max(dy.abs());
+            (start.0 + side.copysign(dx), start.1 + side.copysign(dy))
+        }
+        Tool::Pen | Tool::Highlighter => end,
+    }
+}
+
+/// A primitive in image pixels. Colours are straight (not premultiplied) RGBA.
+#[derive(Debug, Clone, PartialEq)]
+pub enum Prim {
+    Stroke {
+        points: Vec<P>,
+        width: f32,
+        color: [u8; 4],
+        closed: bool,
+        /// Round caps and joins; false means butt caps.
+        round: bool,
+    },
+    /// A convex polygon.
+    Fill { points: Vec<P>, color: [u8; 4] },
+}
+
+pub fn geometry(shape: &Shape) -> Vec<Prim> {
+    let [r, g, b] = shape.style.color;
+    let opaque = [r, g, b, 255];
+    let w = shape.style.width;
+    let pts = &shape.points;
+    let stroke = |points: Vec<P>, closed: bool| Prim::Stroke {
+        points,
+        width: w,
+        color: opaque,
+        closed,
+        round: true,
+    };
+    match shape.tool {
+        Tool::Line => vec![stroke(vec![pts[0], pts[1]], false)],
+        Tool::Arrow => arrow(pts[0], pts[1], w, opaque),
+        Tool::Rectangle => {
+            let ((x0, y0), (x1, y1)) = (pts[0], pts[1]);
+            vec![stroke(vec![(x0, y0), (x1, y0), (x1, y1), (x0, y1)], true)]
+        }
+        Tool::Ellipse => {
+            let ((x0, y0), (x1, y1)) = (pts[0], pts[1]);
+            let (cx, cy, rx, ry) = (
+                (x0 + x1) / 2.0,
+                (y0 + y1) / 2.0,
+                (x1 - x0).abs() / 2.0,
+                (y1 - y0).abs() / 2.0,
+            );
+            vec![stroke(polygon(cx, cy, rx, ry, ELLIPSE_POINTS), true)]
+        }
+        Tool::Pen if pts.len() == 1 => {
+            let (x, y) = pts[0];
+            vec![Prim::Fill {
+                points: polygon(x, y, w / 2.0, w / 2.0, 24),
+                color: opaque,
+            }]
+        }
+        Tool::Pen => vec![stroke(pts.clone(), false)],
+        Tool::Highlighter => vec![Prim::Stroke {
+            points: pts.clone(),
+            width: w * 4.0,
+            color: [r, g, b, HIGHLIGHT_ALPHA],
+            closed: false,
+            round: false,
+        }],
+    }
+}
+
+/// A line to the base of a filled head whose tip is at `end`.
+fn arrow(start: P, end: P, width: f32, color: [u8; 4]) -> Vec<Prim> {
+    let (dx, dy) = (end.0 - start.0, end.1 - start.1);
+    let len = dx.hypot(dy).max(f32::EPSILON);
+    let (ux, uy) = (dx / len, dy / len);
+    let head = (4.0 * width).max(12.0).min(len);
+    let half = head * 30f32.to_radians().tan();
+    let base = (end.0 - ux * head, end.1 - uy * head);
+    vec![
+        Prim::Stroke {
+            points: vec![start, base],
+            width,
+            color,
+            closed: false,
+            round: true,
+        },
+        Prim::Fill {
+            points: vec![
+                end,
+                (base.0 - uy * half, base.1 + ux * half),
+                (base.0 + uy * half, base.1 - ux * half),
+            ],
+            color,
+        },
+    ]
+}
+
+/// `n` points around an ellipse, starting at angle 0.
+fn polygon(cx: f32, cy: f32, rx: f32, ry: f32, n: usize) -> Vec<P> {
+    (0..n)
+        .map(|i| {
+            let a = i as f32 / n as f32 * std::f32::consts::TAU;
+            (cx + rx * a.cos(), cy + ry * a.sin())
+        })
+        .collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const RED: Style = Style {
+        color: [255, 59, 48],
+        width: 4.0,
+    };
+
+    fn shape(tool: Tool, points: &[(f32, f32)]) -> Shape {
+        Shape {
+            tool,
+            style: RED,
+            points: points.to_vec(),
+        }
+    }
+
+    fn close(a: (f32, f32), b: (f32, f32)) -> bool {
+        (a.0 - b.0).abs() < 1e-3 && (a.1 - b.1).abs() < 1e-3
+    }
+
+    #[test]
+    fn shift_snaps_lines_to_45_degrees() {
+        let end = constrain(Tool::Line, (0.0, 0.0), (100.0, 10.0), true);
+        assert!(close(end, ((100f32.hypot(10.0)), 0.0)), "{end:?}");
+        let end = constrain(Tool::Arrow, (0.0, 0.0), (50.0, 45.0), true);
+        let d = 50f32.hypot(45.0) / 2f32.sqrt();
+        assert!(close(end, (d, d)), "{end:?}");
+        assert_eq!(
+            constrain(Tool::Line, (0.0, 0.0), (100.0, 10.0), false),
+            (100.0, 10.0)
+        );
+    }
+
+    #[test]
+    fn shift_makes_squares_and_circles() {
+        assert_eq!(
+            constrain(Tool::Rectangle, (10.0, 10.0), (40.0, 20.0), true),
+            (40.0, 40.0)
+        );
+        assert_eq!(
+            constrain(Tool::Ellipse, (10.0, 10.0), (0.0, 60.0), true),
+            (-40.0, 60.0)
+        );
+    }
+
+    #[test]
+    fn clicks_are_discarded_but_a_pen_dot_is_kept() {
+        assert!(shape(Tool::Arrow, &[(5.0, 5.0), (6.0, 6.0)]).is_click());
+        assert!(!shape(Tool::Arrow, &[(5.0, 5.0), (8.0, 5.0)]).is_click());
+        assert!(shape(Tool::Highlighter, &[(5.0, 5.0), (5.5, 5.0)]).is_click());
+        assert!(!shape(Tool::Pen, &[(5.0, 5.0)]).is_click());
+    }
+
+    #[test]
+    fn arrow_has_a_line_and_a_head_at_the_end() {
+        let g = geometry(&shape(Tool::Arrow, &[(0.0, 0.0), (100.0, 0.0)]));
+        assert_eq!(g.len(), 2);
+        let Prim::Stroke { points, width, .. } = &g[0] else {
+            panic!("{g:?}")
+        };
+        assert_eq!(*width, 4.0);
+        assert!(
+            close(points[0], (0.0, 0.0)) && close(points[1], (84.0, 0.0)),
+            "{points:?}"
+        );
+        let Prim::Fill { points, .. } = &g[1] else {
+            panic!("{g:?}")
+        };
+        // Head length max(12, 4 × 4) = 16, half-width 16 × tan 30°.
+        let half = 16.0 * (30f32).to_radians().tan();
+        assert!(close(points[0], (100.0, 0.0)), "{points:?}");
+        assert!(
+            close(points[1], (84.0, half)) && close(points[2], (84.0, -half)),
+            "{points:?}"
+        );
+    }
+
+    #[test]
+    fn highlighter_is_wide_and_translucent() {
+        let g = geometry(&shape(Tool::Highlighter, &[(0.0, 0.0), (50.0, 0.0)]));
+        let Prim::Stroke {
+            width,
+            color,
+            round,
+            ..
+        } = &g[0]
+        else {
+            panic!("{g:?}")
+        };
+        assert_eq!(*width, 16.0);
+        assert_eq!(*color, [255, 59, 48, 102]);
+        assert!(!round, "butt caps: overlapping caps would darken");
+    }
+
+    #[test]
+    fn rectangle_and_ellipse_are_closed_outlines() {
+        let g = geometry(&shape(Tool::Rectangle, &[(10.0, 10.0), (0.0, 20.0)]));
+        let Prim::Stroke { points, closed, .. } = &g[0] else {
+            panic!("{g:?}")
+        };
+        assert!(*closed);
+        assert_eq!(
+            points,
+            &[(10.0, 10.0), (0.0, 10.0), (0.0, 20.0), (10.0, 20.0)]
+        );
+        let g = geometry(&shape(Tool::Ellipse, &[(0.0, 0.0), (20.0, 10.0)]));
+        let Prim::Stroke { points, closed, .. } = &g[0] else {
+            panic!("{g:?}")
+        };
+        assert!(*closed && points.len() == 72);
+        assert!(
+            points
+                .iter()
+                .all(|p| ((p.0 - 10.0) / 10.0).powi(2) + ((p.1 - 5.0) / 5.0).powi(2) - 1.0 < 1e-3)
+        );
+    }
+
+    #[test]
+    fn a_pen_dot_is_a_filled_circle() {
+        let g = geometry(&shape(Tool::Pen, &[(5.0, 5.0)]));
+        let Prim::Fill { points, color } = &g[0] else {
+            panic!("{g:?}")
+        };
+        assert_eq!(*color, [255, 59, 48, 255]);
+        assert!(
+            points
+                .iter()
+                .all(|p| ((p.0 - 5.0).hypot(p.1 - 5.0) - 2.0).abs() < 1e-3)
+        );
+    }
+
+    #[test]
+    fn drag_collects_points_per_tool() {
+        let mut d = Drag::new(Tool::Pen, RED, (0.0, 0.0));
+        d.move_to((1.0, 1.0));
+        d.move_to((2.0, 3.0));
+        assert_eq!(
+            d.shape(false).points,
+            vec![(0.0, 0.0), (1.0, 1.0), (2.0, 3.0)]
+        );
+        let mut d = Drag::new(Tool::Rectangle, RED, (0.0, 0.0));
+        d.move_to((5.0, 9.0));
+        d.move_to((30.0, 10.0));
+        assert_eq!(d.shape(false).points, vec![(0.0, 0.0), (30.0, 10.0)]);
+        assert_eq!(d.shape(true).points, vec![(0.0, 0.0), (30.0, 30.0)]);
+    }
+}