Basic support for plotly backend

NOTE: this requires you to clone `plotly`, copy the
`plotly_kaleido` folder to be adjacent to this one, and then run `cargo
build --release` from within that plotly_kaleido folder.

src/render.rs

@@ -1,11 +1,13 @@
 use ansi_term::Color::RGB;
-use crate::geom::{Meters, Vec2, Vec3};
+use crate::geom::{Index, Meters, Vec2, Vec3, Vec3u};
 use crate::{flt::{Flt, Real}, Material as _};
 use crate::mat;
 use crate::sim::{Cell, GenericSim};
 use crate::meas::AbstractMeasurement;
 use font8x8::{BASIC_FONTS, GREEK_FONTS, UnicodeFonts as _};
 use log::{trace, info};
+use plotly::{Plot, ImageFormat};
+use plotly::heat_map::HeatMap;
 use image::{RgbImage, Rgb};
 use imageproc::{pixelops, drawing};
 use std::fs::File;
@@ -324,6 +326,33 @@ impl Renderer for Y4MRenderer {
     }
 }
 
+pub struct PlotlyRenderer;
+
+impl Renderer for PlotlyRenderer {
+    fn render(&mut self, state: &dyn GenericSim, measurements: &[Box<dyn AbstractMeasurement>]) {
+        let mut plot = Plot::new();
+        let mut xv = Vec::new();
+        let mut yv = Vec::new();
+        let mut zv = Vec::new();
+        for z in 0..state.depth() {
+            for y in 0..state.height() {
+                for x in 0..state.width() {
+                    let cell = state.get(Index(Vec3u::new(x, y, z)));
+                    if cell.e().mag() > 10.0 {
+                        xv.push(x);
+                        yv.push(y);
+                        zv.push(z);
+                    }
+                }
+            }
+        }
+        let heat_map = HeatMap::new(xv, yv, zv);
+        plot.add_trace(heat_map);
+        let name = format!("frame{}", state.step_no());
+        plot.save(&*name, ImageFormat::PNG, state.width() as _, state.height() as _, 1.0);
+    }
+}
+
 #[derive(Default)]
 pub struct MultiRenderer {
     renderers: Vec<Box<dyn Renderer>>,