why is my slider rendering wrong

Cargo.lock

@@ -1132,7 +1132,7 @@ checksum = "c7d73b3f436185384286bd8098d17ec07c9a7d2388a6599f824d8502b529702a"
 [[package]]
 name = "libosu"
 version = "0.0.12"
-source = "git+https://github.com/iptq/libosu?rev=7acc09af59b789f78c21c259d4e1e246e9cf0b08#7acc09af59b789f78c21c259d4e1e246e9cf0b08"
+source = "git+https://github.com/iptq/libosu?rev=5a8501aec0f4f2232507f80a65b8b31be8756414#5a8501aec0f4f2232507f80a65b8b31be8756414"
 dependencies = [
  "anyhow",
  "bitflags",

Cargo.toml

@@ -19,4 +19,4 @@ num = "0.3.1"
 
 [dependencies.libosu]
 git = "https://github.com/iptq/libosu"
-rev = "7acc09af59b789f78c21c259d4e1e246e9cf0b08"
+rev = "5a8501aec0f4f2232507f80a65b8b31be8756414"

src/game.rs

@@ -6,7 +6,8 @@ use anyhow::Result;
 use ggez::{
     event::{EventHandler, KeyCode, KeyMods},
     graphics::{
-        self, DrawMode, DrawParam, FillOptions, FilterMode, Mesh, Rect, StrokeOptions, Text, WHITE,
+        self, Color, DrawMode, DrawParam, FillOptions, FilterMode, Mesh, Rect, StrokeOptions, Text,
+        WHITE,
     },
     Context, GameError, GameResult,
 };
@@ -68,6 +69,14 @@ impl Game {
 
         graphics::clear(ctx, [0.0, 0.0, 0.0, 1.0].into());
 
+        let playfield = Mesh::new_rectangle(
+            ctx,
+            DrawMode::Stroke(StrokeOptions::default()),
+            EDITOR_SCREEN,
+            Color::new(1.0, 1.0, 1.0, 0.5),
+        )?;
+        graphics::draw(ctx, &playfield, DrawParam::default())?;
+
         let time = self.song.as_ref().unwrap().position()?;
         let text = Text::new(format!("time: {}", time).as_ref());
         graphics::queue_text(ctx, &text, [0.0, 0.0], Some(WHITE));
@@ -84,7 +93,7 @@ impl Game {
 
         let osupx_scale_x = EDITOR_SCREEN.w / 512.0;
         let osupx_scale_y = EDITOR_SCREEN.h / 384.0;
-        let cs_osupx = 54.4 - 4.48 * self.beatmap.difficulty.circle_size;
+        let cs_osupx = self.beatmap.difficulty.circle_size_osupx();
         let cs_real = cs_osupx * osupx_scale_x;
 
         for ho in visible_hitobjects.iter() {

src/slider_render.rs

@@ -1,13 +1,8 @@
-use std::collections::{HashMap, VecDeque};
+use std::collections::VecDeque;
-use std::mem;
-use std::sync::Arc;
 
 use anyhow::Result;
 use ggez::{
-    conf::NumSamples,
+    graphics::{self, DrawMode, DrawParam, LineCap, LineJoin, Mesh, Rect, StrokeOptions},
-    graphics::{
-        self, Canvas, Color, DrawMode, DrawParam, LineCap, LineJoin, Mesh, Rect, StrokeOptions,
-    },
     nalgebra::Point2,
     Context,
 };
@@ -32,7 +27,7 @@ pub fn render_slider(
 
     let osupx_scale_x = rect.w as f64 / 512.0;
     let osupx_scale_y = rect.h as f64 / 384.0;
-    let cs_osupx = 54.4 - 4.48 * beatmap.difficulty.circle_size as f64;
+    let cs_osupx = beatmap.difficulty.circle_size_osupx() as f64;
     let cs_real = cs_osupx * osupx_scale_x;
 
     let (mut boundx, mut boundy, mut boundw, mut boundh) = (0.0f64, 0.0f64, 0.0f64, 0.0f64);
@@ -75,9 +70,14 @@ fn get_spline(
     let points = control_points
         .iter()
         .map(|p| Point(p.0 as f64, p.1 as f64))
-        .collect();
+        .collect::<Vec<_>>();
     match kind {
-        SliderSplineKind::Linear => points,
+        SliderSplineKind::Linear => {
+            let start = points[0];
+            let unit = (points[1] - points[0]).norm();
+            let end = points[0] + unit * pixel_length;
+            vec![start, end]
+        }
         SliderSplineKind::Perfect => {
             let (p1, p2, p3) = (points[0], points[1], points[2]);
             let (center, radius) = Math::circumcircle(p1, p2, p3);