Fix boundaries

src/char.rs

@@ -23,9 +23,9 @@ impl SimpleCharSampler {
 
 impl CharSampler for SimpleCharSampler {
     fn sample(&self, level: f32) -> char {
-        let index = level * self.chars.chars().count() as f32;
+        assert!(0.0 <= level && level < 1.0);
 
-        assert!(index >= 0.0);
+        let index = level * self.chars.chars().count() as f32;
 
         self.chars.chars().nth(index as usize).unwrap()
     }

src/color.rs

@@ -22,9 +22,9 @@ impl SimpleColorSampler {
 
 impl ColorSampler for SimpleColorSampler {
     fn sample(&self, fill: f32) -> Color {
-        let index = self.values.len() as f32 * fill;
+        assert!(0.0 <= fill && fill < 1.0);
 
-        assert!(index >= 0.0);
+        let index = self.values.len() as f32 * fill;
 
         self.values[index as usize]
     }

src/sampler.rs

@@ -37,9 +37,9 @@ impl Sampler for ComposedSampler {
     fn sample(&self, step: f32, pos: Vector) -> Sample {
         let level = self.animation.sample(step, pos);
 
-        if level > 1.0 {
+        if level >= 1.0 {
             Sample::Keep
-        } else if level > 0.0 {
+        } else if level >= 0.0 {
             let char = self.char.sample(level);
             let fill = self.fill.sample(level, pos);
             let color = self.color.sample(fill);
@@ -104,4 +104,36 @@ mod test {
 
         assert!(matches!(sampler.sample(0.7, Vector::new(0.3, 0.1)), Sample::Clear));
     }
+
+    #[test]
+    fn sample_almost_draw() {
+        let mut anim = Box::new(MockAnimation::new());
+        let fill = Box::new(MockFillMode::new());
+        let color = Box::new(MockColorSampler::new());
+        let char = Box::new(MockCharSampler::new());
+
+        anim.expect_sample().return_const(1.0);
+
+        let sampler = ComposedSampler::new(anim, fill, color, char);
+
+        assert!(matches!(sampler.sample(0.7, Vector::new(0.3, 0.1)), Sample::Keep));
+    }
+
+
+    #[test]
+    fn sample_almost_clear() {
+        let mut anim = Box::new(MockAnimation::new());
+        let mut fill = Box::new(MockFillMode::new());
+        let mut color = Box::new(MockColorSampler::new());
+        let mut char = Box::new(MockCharSampler::new());
+
+        anim.expect_sample().return_const(0.0);
+        fill.expect_sample().return_const(0.8);
+        color.expect_sample().return_const(Color::Blue);
+        char.expect_sample().return_const('a');
+
+        let sampler = ComposedSampler::new(anim, fill, color, char);
+
+        assert!(matches!(sampler.sample(0.7, Vector::new(0.3, 0.1)), Sample::Draw { .. }));
+    }
 }