feat: Add spectrum analyzer using Parenscript

Implements real-time audio visualization for the main page:
- Added Parenscript dependency to asteroid.asd
- Created spectrum-analyzer.lisp with Parenscript code
- Added canvas element to front-page.ctml above nav buttons
- Auto-generates JavaScript at compile time
- Green gradient bars matching Asteroid aesthetic
- Uses Web Audio API for FFT analysis

This is the first Parenscript component in Asteroid Radio,
demonstrating the approach for future JavaScript conversions.

SPECTRUM-ANALYZER.org

@@ -0,0 +1,62 @@
+#+TITLE: Spectrum Analyzer Implementation
+#+AUTHOR: Asteroid Radio
+#+DATE: 2025-12-02
+
+* Overview
+Real-time audio spectrum analyzer for Asteroid Radio, implemented using Parenscript (Lisp-to-JavaScript compiler).
+
+* Features
+- *Real-time visualization* of audio frequencies using Web Audio API
+- *Green gradient bars* matching Asteroid Radio's aesthetic
+- *Smooth animations* with fade effects
+- *Responsive design* - canvas scales to fit container
+- *Auto-start* - begins when audio playback starts
+
+* Implementation Details
+
+** Files Modified
+1. *asteroid.asd* - Added Parenscript dependency
+2. *spectrum-analyzer.lisp* - Parenscript code that generates JavaScript
+3. *module.lisp* - Compile-time hook to generate JS file
+4. *template/front-page.ctml* - Added canvas element and script tag
+
+** Technical Approach
+- Uses *Web Audio API* =AnalyserNode= for FFT analysis
+- *256 frequency bins* for balanced detail and performance
+- *Canvas 2D* rendering with gradient fills
+- *RequestAnimationFrame* for smooth 60fps animation
+- *Event-driven* - starts on audio play, stops on pause
+
+** Parenscript Benefits
+- *Type safety* - Lisp macros catch errors at compile time
+- *Code reuse* - Share utilities between server and client
+- *Maintainability* - Single language for full stack
+- *Integration* - Seamless with existing Radiance/Clip infrastructure
+
+* Usage
+
+** Generating JavaScript
+The JavaScript is automatically generated at compile time. To manually regenerate:
+
+#+BEGIN_SRC lisp
+(asteroid:write-spectrum-analyzer-js)
+#+END_SRC
+
+This creates =static/js/spectrum-analyzer.js= from the Parenscript code.
+
+** Customization
+Edit =spectrum-analyzer.lisp= to modify:
+- *FFT size* - =(setf (@ *analyser* fft-size) 256)=
+- *Colors* - Gradient color stops in =draw-spectrum=
+- *Smoothing* - =(setf (@ *analyser* smoothing-time-constant) 0.8)=
+- *Canvas size* - Update width/height in template
+
+* Future Enhancements
+- Multiple visualization modes (waveform, circular, particle effects)
+- User-selectable color schemes
+- Frequency range filtering
+- Beat detection and reactive animations
+- Integration with now-playing metadata
+
+* Notes
+This is the first Parenscript component in Asteroid Radio. Future work will convert existing JavaScript files to Parenscript as part of the =glenneth/parenscript-conversion= branch.

asteroid.asd

@@ -15,6 +15,7 @@
                :cl-json
                :radiance
                :lass
+               :parenscript
                :local-time
                :taglib
                :ironclad
@@ -31,7 +32,6 @@
                :r-simple-rate
                (:interface :auth)
                (:interface :database)
-               (:interface :relational-database)
                (:interface :user))
   :pathname "./"
   :components ((:file "app-utils")
@@ -41,6 +41,7 @@
                (:file "conditions")
                (:file "database")
                (:file "template-utils")
+               (:file "spectrum-analyzer")
                (:file "stream-media")
                (:file "user-management")
                (:file "playlist-management")

module.lisp

@@ -4,3 +4,10 @@
   (:use #:cl #:radiance #:lass #:r-clip #:asteroid.app-utils)
   (:domain "asteroid")
   (:export #:-main))
+
+;; Generate Parenscript files at compile time
+(eval-when (:compile-toplevel :load-toplevel :execute)
+  (when (find-package :asteroid)
+    (let ((pkg (find-package :asteroid)))
+      (when (fboundp (find-symbol "WRITE-SPECTRUM-ANALYZER-JS" pkg))
+        (funcall (find-symbol "WRITE-SPECTRUM-ANALYZER-JS" pkg))))))

spectrum-analyzer.lisp

@@ -0,0 +1,96 @@
+(in-package #:asteroid)
+
+;;; Spectrum Analyzer - Parenscript Implementation
+;;; Generates JavaScript for real-time audio visualization
+
+(defun generate-spectrum-analyzer-js ()
+  "Generate JavaScript code for the spectrum analyzer using Parenscript"
+  (ps:ps
+    (defvar *audio-context* nil)
+    (defvar *analyser* nil)
+    (defvar *canvas* nil)
+    (defvar *canvas-ctx* nil)
+    (defvar *animation-id* nil)
+    
+    (defun init-spectrum-analyzer ()
+      "Initialize the spectrum analyzer"
+      (let ((audio-element (chain document (get-element-by-id "live-audio")))
+            (canvas-element (chain document (get-element-by-id "spectrum-canvas"))))
+        
+        (when (and audio-element canvas-element)
+          ;; Create Audio Context
+          (setf *audio-context* (new (or (@ window -audio-context)
+                                         (@ window -webkit-audio-context))))
+          
+          ;; Create Analyser Node
+          (setf *analyser* (chain *audio-context* (create-analyser)))
+          (setf (@ *analyser* fft-size) 256)
+          (setf (@ *analyser* smoothing-time-constant) 0.8)
+          
+          ;; Connect audio source to analyser
+          (let ((source (chain *audio-context* (create-media-element-source audio-element))))
+            (chain source (connect *analyser*))
+            (chain *analyser* (connect (@ *audio-context* destination))))
+          
+          ;; Setup canvas
+          (setf *canvas* canvas-element)
+          (setf *canvas-ctx* (chain *canvas* (get-context "2d")))
+          
+          ;; Start visualization
+          (draw-spectrum))))
+    
+    (defun draw-spectrum ()
+      "Draw the spectrum analyzer visualization"
+      (setf *animation-id* (request-animation-frame draw-spectrum))
+      
+      (let* ((buffer-length (@ *analyser* frequency-bin-count))
+             (data-array (new (-uint8-array buffer-length)))
+             (width (@ *canvas* width))
+             (height (@ *canvas* height))
+             (bar-width (/ width buffer-length))
+             (bar-height 0)
+             (x 0))
+        
+        (chain *analyser* (get-byte-frequency-data data-array))
+        
+        ;; Clear canvas with fade effect
+        (setf (@ *canvas-ctx* fill-style) "rgba(0, 0, 0, 0.2)")
+        (chain *canvas-ctx* (fill-rect 0 0 width height))
+        
+        ;; Draw bars
+        (dotimes (i buffer-length)
+          (setf bar-height (/ (* (aref data-array i) height) 256))
+          
+          ;; Create gradient for each bar
+          (let ((gradient (chain *canvas-ctx* 
+                                (create-linear-gradient 0 (- height bar-height) 0 height))))
+            (chain gradient (add-color-stop 0 "#00ff00"))
+            (chain gradient (add-color-stop 0.5 "#00aa00"))
+            (chain gradient (add-color-stop 1 "#005500"))
+            
+            (setf (@ *canvas-ctx* fill-style) gradient)
+            (chain *canvas-ctx* (fill-rect x (- height bar-height) bar-width bar-height))
+            
+            (incf x bar-width)))))
+    
+    (defun stop-spectrum-analyzer ()
+      "Stop the spectrum analyzer"
+      (when *animation-id*
+        (cancel-animation-frame *animation-id*)
+        (setf *animation-id* nil)))
+    
+    ;; Initialize when audio starts playing
+    (chain document (add-event-listener "DOMContentLoaded"
+      (lambda ()
+        (let ((audio-element (chain document (get-element-by-id "live-audio"))))
+          (when audio-element
+            (chain audio-element (add-event-listener "play" init-spectrum-analyzer))
+            (chain audio-element (add-event-listener "pause" stop-spectrum-analyzer)))))))))
+
+(defun write-spectrum-analyzer-js ()
+  "Write the generated JavaScript to a file"
+  (with-open-file (stream (asdf:system-relative-pathname :asteroid "static/js/spectrum-analyzer.js")
+                          :direction :output
+                          :if-exists :supersede
+                          :if-does-not-exist :create)
+    (write-string (generate-spectrum-analyzer-js) stream)))

template/front-page.ctml

@@ -11,6 +11,7 @@
   <script src="/asteroid/static/js/auth-ui.js"></script>
   <script src="/asteroid/static/js/front-page.js"></script>
   <script src="/asteroid/static/js/recently-played.js"></script>
+  <script src="/asteroid/static/js/spectrum-analyzer.js"></script>
 </head>
 <body>
   <div class="container">
@@ -21,6 +22,12 @@
         <img src="/asteroid/static/asteroid.png" alt="Asteroid" style="height: 60px; width: auto;">
       </h1>
       <h3 class="page-subtitle">The Station at the End of Time</h3>
+      
+      <!-- Spectrum Analyzer Canvas -->
+      <div style="text-align: center; margin: 15px 0;">
+        <canvas id="spectrum-canvas" width="800" height="100" style="max-width: 100%; border: 1px solid #00ff00; background: #000; border-radius: 4px;"></canvas>
+      </div>
+      
       <nav class="nav">
         <a href="/asteroid/">Home</a>
         <a href="/asteroid/player">Player</a>