fixing path trace cases that wind up with points too squished together

docs/TODO_quality.md

@@ -5,6 +5,7 @@
 - try fixed pt again, for determinism purposes mostly
 	- successful: Lines of ~0 length gone
 	- but due to bad polyline shifting, some things would loudly break if we squished pts down always
+	- might be cleaner to make polyline slice return Optional
 
 - underlying problems
 	- bad polyline shifting remains

geom/src/polyline.rs

@@ -162,6 +162,15 @@ impl PolyLine {
                 self.length()
             );
         }
+        if result.len() == 1 {
+            panic!(
+                "Slice [{}, {}] didn't work on a polyline of length {} with points {}",
+                start,
+                end,
+                self.length(),
+                self
+            );
+        }
 
         (PolyLine::new(result), end - dist_so_far)
     }

map_model/src/pathfind.rs

@@ -1,6 +1,6 @@
 use crate::{BusRouteID, BusStopID, LaneID, LaneType, Map, Position, Traversable, TurnID};
 use dimensioned::si;
-use geom::{PolyLine, Pt2D};
+use geom::{PolyLine, Pt2D, EPSILON_DIST};
 use ordered_float::NotNan;
 use serde_derive::{Deserialize, Serialize};
 use std::collections::{BinaryHeap, HashMap, VecDeque};
@@ -85,14 +85,14 @@ impl PathStep {
             PathStep::Lane(id) => {
                 let l = map.get_l(*id);
                 // Might have a pedestrian at a front_path lined up with the end of a lane
-                if start == l.length() {
+                if start >= l.length() - EPSILON_DIST {
                     None
                 } else {
                     Some(l.lane_center_pts.slice(start, start + dist_ahead))
                 }
             }
             PathStep::ContraflowLane(id) => {
-                if start == 0.0 * si::M {
+                if start < EPSILON_DIST {
                     None
                 } else {
                     let pts = map.get_l(*id).lane_center_pts.reversed();
@@ -102,7 +102,7 @@ impl PathStep {
             }
             PathStep::Turn(id) => {
                 let geom = &map.get_t(*id).geom;
-                if geom.length() == 0.0 * si::M {
+                if start >= geom.length() - EPSILON_DIST {
                     None
                 } else {
                     Some(geom.slice(start, start + dist_ahead))
@@ -227,6 +227,7 @@ impl Path {
                 PathStep::ContraflowLane(l) => map.get_l(l).lane_center_pts.reversed().length(),
                 _ => 0.0 * si::M,
             };
+            if dist_remaining - start_dist_this_step > EPSILON_DIST {
                 if let Some((new_pts, dist)) =
                     self.steps[i].slice(map, start_dist_this_step, dist_remaining)
                 {
@@ -239,6 +240,7 @@ impl Path {
                     dist_remaining = dist;
                 }
             }
+        }
 
         Some(pts_so_far.unwrap())
     }

sim/src/driving.rs

@@ -851,7 +851,13 @@ impl DrivingSimState {
             )
             .unwrap()
         } else {
+            if c.dist_along > EPSILON_DIST {
                 c.on.slice(0.0 * si::M, c.dist_along, map).0
+            } else {
+                // TODO Kinda weird to consider the car not present, but eventually cars spawning
+                // at borders should appear fully anyway.
+                return None;
+            }
         };
 
         let body = if let Some(ref parking) = c.parking {