Basic single-channel rendering

Cargo.toml

@@ -25,4 +25,5 @@ features = [
   "AudioContext",
   "AudioBuffer",
   "HtmlCanvasElement",
+  "CanvasRenderingContext2d",
 ]

src/canvas.rs

@@ -1,4 +1,6 @@
 use crate::agents::audio_agent::{AudioAgent, AudioData};
+use crate::utils;
+use wasm_bindgen::JsCast;
 use web_sys::HtmlCanvasElement;
 use yew::agent::Bridged;
 use yew::prelude::*;
@@ -59,15 +61,60 @@ impl Canvas {
     }
 
     fn handle_samples_loaded_error(&mut self, err: &str) {
-        self.reset();
-
         ConsoleService::error(&format!("Error loading samples: {}", err));
+
+        self.audio_data = None;
+        self.redraw_canvas();
     }
 
     fn redraw_canvas(&mut self) {
         let canvas_element = self.canvas_node.cast::<HtmlCanvasElement>().unwrap();
-        let _context = canvas_element.get_context("2d").unwrap();
-        // TODO: draw canvas...
-        ConsoleService::log("TODO: draw on canvas...");
+        // canvas_element.clear(); TODO
+
+        let width = canvas_element.width();
+        let height = canvas_element.height();
+
+        // TODO: error handling
+        let context = canvas_element
+            .get_context("2d")
+            .unwrap()
+            .unwrap()
+            .dyn_into::<web_sys::CanvasRenderingContext2d>()
+            .unwrap();
+
+        context.set_fill_style(&"black".into());
+        context.set_stroke_style(&"green".into());
+        context.fill_rect(0.0, 0.0, width as f64, height as f64);
+
+        // TODO: improve
+        if self.audio_data.is_none() {
+            return;
+        }
+        let audio_data = self.audio_data.as_ref().unwrap();
+
+        // TODO: multi-channel
+        let _num_channels = audio_data.number_of_channels(); // 1
+
+        let channel_data = audio_data.get_channel_data(0).unwrap();
+        let chunks = utils::chunks_fixed(&channel_data, width as usize);
+
+        chunks.enumerate().for_each(|(i, chunk)| {
+            let max = chunk
+                .iter()
+                .map(|v| (v * 32767.0) as i32)
+                .map(|v| v.abs())
+                .max()
+                .unwrap();
+
+            let pc = (max as f64 / 32767.0) * 100.0;
+            let len = (height as f64 / 100.0 * pc).floor();
+            let mid = height as f64 / 2f64;
+
+            context.begin_path();
+            context.move_to(i as f64, mid - (len / 2f64));
+            context.line_to(i as f64, mid + (len / 2f64));
+            context.stroke();
+            // ConsoleService::log(&format!("index {}: max {}, pc {}, len {}", i, max, pc, len));
+        });
     }
 }