add a RenderedVectorField. maybe more accurately called a rendered stimulus?

used to represent a stimulus which has been rendered for a specific time with specific simulation parameters.

crates/coremem/src/stim.rs

@@ -153,6 +153,52 @@ where
     }
 }
 
+pub struct RenderedVectorField {
+    e: DimSlice<Vec<Vec3<f32>>>,
+    h: DimSlice<Vec<Vec3<f32>>>,
+    scale: f32,
+    feature_size: f32,
+    t_sec: f32,
+}
+
+impl RenderedVectorField {
+    pub fn new(
+        e: DimSlice<Vec<Vec3<f32>>>,
+        h: DimSlice<Vec<Vec3<f32>>>,
+        scale: f32,
+        feature_size: f32,
+        t_sec: f32,
+    ) -> Self {
+        Self { e, h, scale, feature_size, t_sec }
+    }
+    pub fn e<'a>(&'a self) -> DimSlice<&'a [Vec3<f32>]> {
+        self.e.as_ref()
+    }
+    pub fn h<'a>(&'a self) -> DimSlice<&'a [Vec3<f32>]> {
+        self.h.as_ref()
+    }
+    pub fn scale(&self) -> f32 {
+        self.scale
+    }
+    pub fn feature_size(&self) -> f32 {
+        self.feature_size
+    }
+    pub fn time(&self) -> f32 {
+        self.t_sec
+    }
+}
+
+impl VectorField for RenderedVectorField {
+    fn at(&self, _feat_size: f32, loc: Index) -> Fields {
+        Fields::new_eh(self.e[loc.into()], self.h[loc.into()])
+    }
+}
+impl Stimulus for RenderedVectorField {
+    fn at(&self, _t_sec: f32, _feat_size: f32, loc: Index) -> Fields {
+        Fields::new_eh(self.e[loc.into()], self.h[loc.into()])
+    }
+}
+
 impl Stimulus for Fields {
     fn at(&self, _t_sec: f32, _feat_size: f32, _loc: Index) -> Fields {
         *self
@@ -422,16 +468,24 @@ impl TimeVarying for FieldMags {
 // assumed to represent the E field
 impl TimeVarying for f32 {
     fn at(&self, _t_sec: f32) -> FieldMags {
-        FieldMags { e: *self, h: 0.0 }
+        FieldMags::new_e(*self)
     }
 }
 
+// Vec<T> at any `t_sec` behaves as the sum of all its components at that time.
 impl<T: TimeVarying> TimeVarying for Vec<T> {
     fn at(&self, t_sec: f32) -> FieldMags {
         self.iter().fold(FieldMags::default(), |acc, i| acc + i.at(t_sec))
     }
 }
 
+pub struct UnitEH;
+impl TimeVarying for UnitEH {
+    fn at(&self, _t_sec: f32) -> FieldMags {
+        FieldMags::new_eh(1.0, 1.0)
+    }
+}
+
 /// E field which changes magnitude sinusoidally as a function of t
 #[derive(Clone)]
 pub struct Sinusoid {