Implement viewport selection (#178)

* Begin implementing viewport selection

* Implement viewport click and drag selection for ellipse and rectangle

* Begin implementing line selection

* Remove debug prints

* Run cargo format

* Use DVec2 instead of kurbo::Point

* Line and polyline intersection

* Run cargo format

* Add fix for missing layer panel update

* Replace point selection with box selection

* Formatting

Co-authored-by: Keavon Chambers <keavon@keavon.com>

core/document/src/intersection.rs

@@ -0,0 +1,57 @@
+use glam::DVec2;
+use kurbo::{BezPath, Line, PathSeg, Point, Shape, Vec2};
+
+fn to_point(vec: DVec2) -> Point {
+	Point::new(vec.x, vec.y)
+}
+
+pub fn intersect_quad_bez_path(quad: [DVec2; 4], shape: &BezPath, closed: bool) -> bool {
+	let lines = vec![
+		Line::new(to_point(quad[0]), to_point(quad[1])),
+		Line::new(to_point(quad[1]), to_point(quad[2])),
+		Line::new(to_point(quad[2]), to_point(quad[3])),
+		Line::new(to_point(quad[3]), to_point(quad[0])),
+	];
+	// check if outlines intersect
+	for path_segment in shape.segments() {
+		for line in &lines {
+			if !path_segment.intersect_line(*line).is_empty() {
+				return true;
+			}
+		}
+	}
+	// check if selection is entirely within the shape
+	if closed && shape.contains(to_point(quad[0])) {
+		return true;
+	}
+	// check if shape is entirely within the selection
+	if let Some(shape_point) = get_arbitrary_point_on_path(shape) {
+		let mut pos = 0;
+		let mut neg = 0;
+		for line in lines {
+			if line.p0 == shape_point {
+				return true;
+			};
+			let line_vec = Vec2::new(line.p1.x - line.p0.x, line.p1.y - line.p0.y);
+			let point_vec = Vec2::new(line.p1.x - shape_point.x, line.p1.y - shape_point.y);
+			let cross = line_vec.cross(point_vec);
+			if cross > 0.0 {
+				pos += 1;
+			} else if cross < 0.0 {
+				neg += 1;
+			}
+			if pos > 0 && neg > 0 {
+				return false;
+			}
+		}
+	}
+	true
+}
+
+pub fn get_arbitrary_point_on_path(path: &BezPath) -> Option<Point> {
+	path.segments().next().map(|seg| match seg {
+		PathSeg::Line(line) => line.p0,
+		PathSeg::Quad(quad) => quad.p0,
+		PathSeg::Cubic(cubic) => cubic.p0,
+	})
+}