Clamp NaN to white when converting to integer (#2381)

src/color.rs

@@ -436,17 +436,24 @@ impl<T: Primitive> FromPrimitive<T> for T {
 // Note that in to-integer-conversion we are performing rounding but NumCast::from is implemented
 // as truncate towards zero. We emulate rounding by adding a bias.
 
+// All other special values are clamped inbetween 0.0 and 1.0 (infinities and subnormals)
+// NaN however always maps to NaN therefore we have to force it towards some value.
+// 1.0 (white) was picked as firefox and chrome choose to map NaN to that.
+#[inline]
+fn normalize_float(float: f32, max: f32) -> f32 {
+    let clamped = if !(float < 1.0) { 1.0 } else { float.max(0.0) };
+    (clamped * max).round()
+}
+
 impl FromPrimitive<f32> for u8 {
     fn from_primitive(float: f32) -> Self {
-        let inner = (float.clamp(0.0, 1.0) * u8::MAX as f32).round();
-        NumCast::from(inner).unwrap()
+        NumCast::from(normalize_float(float, u8::MAX as f32)).unwrap()
     }
 }
 
 impl FromPrimitive<f32> for u16 {
     fn from_primitive(float: f32) -> Self {
-        let inner = (float.clamp(0.0, 1.0) * u16::MAX as f32).round();
-        NumCast::from(inner).unwrap()
+        NumCast::from(normalize_float(float, u16::MAX as f32)).unwrap()
     }
 }