egui: fix painted bend direction

src/bin/topola-egui/painter.rs

@@ -1,7 +1,7 @@
 use geo::{CoordsIter, Point, Polygon};
 use topola::{
     geometry::primitive::{PrimitiveShape, PrimitiveShapeTrait},
-    math::Circle,
+    math::{self, Circle},
 };
 
 pub struct Painter<'a> {
@@ -31,12 +31,14 @@ impl<'a> Painter<'a> {
                 let delta_to = bend.to - bend.c.pos;
 
                 let angle_from = delta_from.y().atan2(delta_from.x());
-                let angle_to = delta_to.y().atan2(delta_to.x());
+
+                let cross = math::cross_product(delta_from, delta_to);
+                let dot = math::dot_product(delta_from, delta_to);
+                let angle_step = cross.atan2(dot) / 100.0;
+
                 let mut points: Vec<egui::Pos2> = vec![];
 
-                let angle_step = (angle_to - angle_from) / 100.0;
+                for i in 0..=100 {
-
-                for i in 0..100 {
                     let x = bend.c.pos.x() + bend.c.r * (angle_from + i as f64 * angle_step).cos();
                     let y = bend.c.pos.y() + bend.c.r * (angle_from + i as f64 * angle_step).sin();
                     points.push(self.transform.transform_pos([x as f32, -y as f32].into()));

src/math.rs

@@ -238,6 +238,10 @@ pub fn seq_cross_product(start: Point, stop: Point, reference: Point) -> f64 {
     cross_product((dx1, dy1).into(), (dx2, dy2).into())
 }
 
+pub fn dot_product(v1: Point, v2: Point) -> f64 {
+    v1.x() * v2.x() + v1.y() * v2.y()
+}
+
 pub fn cross_product(v1: Point, v2: Point) -> f64 {
     v1.x() * v2.y() - v1.y() * v2.x()
 }