Adding phosphor decay effect to audio scope.

Last four traces are now stored in traces drawn at trace_intensity.
Gadgetoid#14

Author: Kevin J Walters

effect/effect.hpp

@@ -8,11 +8,12 @@
 
 #pragma once
 
-#include <functional>
+#include <array>
 #include <cmath>
-#include <string>
 #include <cstdint>
 #include <cstddef>
+#include <functional>
+#include <string>
 #include "limits.h"
 
 
@@ -195,18 +196,29 @@ class EffectAudioscopeTuner : public EffectTuner {
                                                     64, 64, 64, 
                                                     Display::WIDTH, 
                                                     Display::HEIGHT - font6.height,
-                                                    'r') { };
+                                                    'r'),
+                                          // traces initialised in start()
+                                          trace_intensity({8, 20, 51, 128}),
+                                          trace_idx(0) { };
     virtual ~EffectAudioscopeTuner() { };
 
   protected:
+    void updateDisplay(void) override;
+    void start(void) override;
+    void init(void) override;
+
+  private:
     constexpr static int8_t Y_MID_POS = (Display::HEIGHT - 1) / 2;
     constexpr static float  y_scale   = float(Display::HEIGHT) / (1 - 2 * INT16_MIN);
+    constexpr static int8_t OFF_SCREEN = INT8_MIN;
+    constexpr static size_t TRACE_NUM = 4;
 
     EffectText freq_text;
-
-    void updateDisplay(void) override;
-    void start(void) override;
-    void init(void) override;
+    std::array<std::array<int8_t, Display::WIDTH>, TRACE_NUM> traces;
+    std::array<uint8_t, TRACE_NUM> trace_intensity;
+    size_t trace_idx;  // indicates oldest trace
+  
+    void drawTraces(void);
 };
 
 

effect/effect_audioscope_tuner.cpp

@@ -95,23 +95,48 @@ void EffectAudioscopeTuner::updateDisplay(void) {
         }
     }
 
-    // TODO add multiple fading passes
+    auto &new_trace = traces[trace_idx];
     for (uint8_t x=0; x < Display::WIDTH; x++) {
         int32_t value = window(signal, 5, waveform_idx);  // returns 0 beyond end of buffer
         int32_t y = Y_MID_POS - int32_t(roundf(value * y_scale));
-        waveform_idx += 10;
-        if (y >=0 && y < Display::HEIGHT) {
-            display.set_pixel(x, y,
-                              0u, 128u, 0u);
+        new_trace[x] = (y >=0 && y < Display::HEIGHT) ? y : OFF_SCREEN;
+        waveform_idx += 1000 / Display::WIDTH;  // TODO tune this based on sample rate
+    }
+    trace_idx = (trace_idx + 1) % traces.size();
+    drawTraces();
+}
+
+void EffectAudioscopeTuner::drawTraces(void) {
+    size_t t_idx = trace_idx;
+    uint8_t intensity_idx = 0;
+    for (size_t idx=0; idx < traces.size(); idx++) {
+        const auto &trace = traces[t_idx++];
+        for (uint8_t x=0; x < Display::WIDTH; x++) {
+            int32_t y = trace[x];
+            if (y >=0 && y < Display::HEIGHT) {
+                display.set_pixel(x, y,
+                                  0u, trace_intensity[idx], 0u);
+            }
+        }
+        if (t_idx >= traces.size()) {
+            t_idx = 0;  // wrap back to the start
         }
-    }             
+    }
 }
 
 void EffectAudioscopeTuner::start(void) {
     display.clear();    
 
     // default step is 1, other effects may have changed it
     tuner.setStep(4);
+
+    // For visual effect, initialise it falling towards 0 scope pos
+    int8_t start_row = Y_MID_POS - ((Y_MID_POS + 1) / 2);
+    for (auto &trace : traces) {
+        for (auto &tx : trace) {
+            tx = start_row;
+        }
+    }
 }
 
 void EffectAudioscopeTuner::init(void) {