viewer: add a render mode to display just the Material

crates/coremem/src/render.rs

@@ -12,6 +12,8 @@ use image::{RgbImage, Rgb};
 use imageproc::{pixelops, drawing};
 use rayon::prelude::*;
 use serde::{Serialize, Deserialize};
+use std::collections::hash_map::DefaultHasher;
+use std::hash::Hasher;
 use std::fs::{File, OpenOptions};
 use std::io::{BufReader, BufWriter, Seek as _, SeekFrom, Write as _};
 use std::path::{Path, PathBuf};
@@ -72,6 +74,7 @@ pub enum FieldDisplayMode {
     EzBxy,
     BCurrent,
     M,
+    Material,
 }
 
 impl FieldDisplayMode {
@@ -81,17 +84,19 @@ impl FieldDisplayMode {
             BzExy => EzBxy,
             EzBxy => BCurrent,
             BCurrent => M,
-            M => BzExy,
+            M => Material,
+            Material => BzExy,
         }
     }
 
     pub fn prev(self) -> Self {
         use FieldDisplayMode::*;
         match self {
-            BzExy => M,
+            BzExy => Material,
             EzBxy => BzExy,
             BCurrent => EzBxy,
             M => BCurrent,
+            Material => M,
         }
     }
 }
@@ -176,6 +181,9 @@ impl<'a, S: AbstractSim> RenderSteps<'a, S> {
             FieldDisplayMode::M => {
                 me.render_m(config.scale);
             }
+            FieldDisplayMode::Material => {
+                me.render_mat(config.scale);
+            }
         }
         me.render_measurements();
         me.im
@@ -232,6 +240,18 @@ impl<'a, S: AbstractSim> RenderSteps<'a, S> {
         self.render_vector_field(Rgb([0xff, 0xff, 0xff]), 1.0e5 * scale, |cell| cell.m().xy().to_f32());
     }
 
+    fn render_mat(&mut self, scale: f32) {
+        unsafe fn to_bytes<T>(d: &T) -> &[u8] {
+            std::slice::from_raw_parts(d as *const T as *const u8, std::mem::size_of::<T>())
+        }
+        self.render_scalar_field(scale, false, 1, |cell| {
+            let mut hasher = DefaultHasher::new();
+            let as_bytes = unsafe { to_bytes(cell.material()) };
+            std::hash::Hash::hash_slice(as_bytes, &mut hasher);
+            hasher.finish() as f32 / (-1i64 as u64 as f32)
+        });
+    }
+
     fn render_vector_field<F>(&mut self, color: Rgb<u8>, typical: f32, measure: F)
     where
         F: Fn(&Sample<'_, S::Real, S::Material>) -> Vec2<f32>