Initial implementation

1 files changed, 142 insertions, 0 deletions

diff --git a/src/geometry.rs b/src/geometry.rs
new file mode 100644
index 0000000..5099ada
--- /dev/null
+++ b/src/geometry.rs
@@ -0,0 +1,142 @@
+/// Represents a line segment
+#[derive(Debug, Clone, Copy)]
+pub struct Line {
+    pub start: (f64, f64),
+    pub end: (f64, f64),
+}
+
+/// Represents a rectangle
+#[derive(Debug, Clone, Copy)]
+pub struct Rect {
+    pub x: f64,
+    pub y: f64,
+    pub width: f64,
+    pub height: f64,
+}
+
+impl Line {
+    pub fn new(start: (f64, f64), end: (f64, f64)) -> Self {
+        Self { start, end }
+    }
+}
+
+impl Rect {
+    pub fn new(x: f64, y: f64, width: f64, height: f64) -> Self {
+        Self {
+            x,
+            y,
+            width,
+            height,
+        }
+    }
+}
+
+/// Checks if a point is inside a rectangle
+pub fn point_in_rect(point: (f64, f64), rect: &Rect) -> bool {
+    point.0 >= rect.x
+        && point.0 <= rect.x + rect.width
+        && point.1 >= rect.y
+        && point.1 <= rect.y + rect.height
+}
+
+/// Checks if two rectangles intersect (AABB collision)
+pub fn rect_intersects_rect(r1: &Rect, r2: &Rect) -> bool {
+    !(r1.x + r1.width < r2.x
+        || r2.x + r2.width < r1.x
+        || r1.y + r1.height < r2.y
+        || r2.y + r2.height < r1.y)
+}
+
+/// Checks if two line segments intersect using parametric equations
+pub fn line_intersects_line(l1: &Line, l2: &Line) -> bool {
+    let x1 = l1.start.0;
+    let y1 = l1.start.1;
+    let x2 = l1.end.0;
+    let y2 = l1.end.1;
+    let x3 = l2.start.0;
+    let y3 = l2.start.1;
+    let x4 = l2.end.0;
+    let y4 = l2.end.1;
+
+    let denom = (x1 - x2) * (y3 - y4) - (y1 - y2) * (x3 - x4);
+    if denom.abs() < 1e-10 {
+        return false; // Parallel or coincident
+    }
+
+    let t = ((x1 - x3) * (y3 - y4) - (y1 - y3) * (x3 - x4)) / denom;
+    let u = -((x1 - x2) * (y1 - y3) - (y1 - y2) * (x1 - x3)) / denom;
+
+    (0.0..=1.0).contains(&t) && (0.0..=1.0).contains(&u)
+}
+
+/// Checks if a line segment intersects a rectangle
+pub fn line_intersects_rect(line: &Line, rect: &Rect) -> bool {
+    // Check if either endpoint is inside the rectangle
+    if point_in_rect(line.start, rect) || point_in_rect(line.end, rect) {
+        return true;
+    }
+
+    // Check intersection with all four edges
+    let edges = [
+        Line::new((rect.x, rect.y), (rect.x + rect.width, rect.y)), // Top
+        Line::new(
+            (rect.x + rect.width, rect.y),
+            (rect.x + rect.width, rect.y + rect.height),
+        ), // Right
+        Line::new(
+            (rect.x + rect.width, rect.y + rect.height),
+            (rect.x, rect.y + rect.height),
+        ), // Bottom
+        Line::new((rect.x, rect.y + rect.height), (rect.x, rect.y)), // Left
+    ];
+
+    edges.iter().any(|edge| line_intersects_line(line, edge))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_point_in_rect() {
+        let rect = Rect::new(10.0, 10.0, 20.0, 20.0);
+        assert!(point_in_rect((15.0, 15.0), &rect));
+        assert!(point_in_rect((10.0, 10.0), &rect));
+        assert!(point_in_rect((30.0, 30.0), &rect));
+        assert!(!point_in_rect((5.0, 15.0), &rect));
+        assert!(!point_in_rect((35.0, 15.0), &rect));
+    }
+
+    #[test]
+    fn test_rect_intersects_rect() {
+        let r1 = Rect::new(0.0, 0.0, 10.0, 10.0);
+        let r2 = Rect::new(5.0, 5.0, 10.0, 10.0);
+        let r3 = Rect::new(20.0, 20.0, 10.0, 10.0);
+
+        assert!(rect_intersects_rect(&r1, &r2));
+        assert!(rect_intersects_rect(&r2, &r1));
+        assert!(!rect_intersects_rect(&r1, &r3));
+    }
+
+    #[test]
+    fn test_line_intersects_line() {
+        let l1 = Line::new((0.0, 0.0), (10.0, 10.0));
+        let l2 = Line::new((0.0, 10.0), (10.0, 0.0));
+        let l3 = Line::new((20.0, 20.0), (30.0, 30.0));
+
+        assert!(line_intersects_line(&l1, &l2));
+        assert!(!line_intersects_line(&l1, &l3));
+    }
+
+    #[test]
+    fn test_line_intersects_rect() {
+        let rect = Rect::new(10.0, 10.0, 20.0, 20.0);
+        let l1 = Line::new((0.0, 15.0), (40.0, 15.0)); // Horizontal through
+        let l2 = Line::new((15.0, 0.0), (15.0, 40.0)); // Vertical through
+        let l3 = Line::new((0.0, 0.0), (5.0, 5.0)); // Outside
+
+        assert!(line_intersects_rect(&l1, &rect));
+        assert!(line_intersects_rect(&l2, &rect));
+        assert!(!line_intersects_rect(&l3, &rect));
+    }
+}