Merge pull request #9 from MichaelBell/log-scale-Y

Log scale Y axis

Author: Gadgetoid

src/btstack_audio_pico.cpp

@@ -252,9 +252,25 @@ static void btstack_audio_pico_sink_fill_buffers(void){
             }
         }
 
+// Choose one:
+//#define SCALE_LOGARITHMIC
+#define SCALE_SQRT
+//#define SCALE_LINEAR
+
+        constexpr float max_sample_from_fft = 4000.f + 130.f * display.HEIGHT;
+        constexpr int lower_threshold = 270 - 2 * display.HEIGHT;
+#ifdef SCALE_LOGARITHMIC
+        constexpr fix15 multiple = float_to_fix15(pow(max_sample_from_fft / lower_threshold, -1.f / (display.HEIGHT - 1)));
+#elif defined(SCALE_SQRT)
+        constexpr fix15 subtract_step = float_to_fix15((max_sample_from_fft - lower_threshold) * 2.f / (display.HEIGHT * (display.HEIGHT - 1)));
+#elif defined(SCALE_LINEAR)
+        constexpr fix15 subtract = float_to_fix15((max_sample_from_fft - lower_threshold) / (display.HEIGHT - 1));
+#else
+    #error "Choose a scale mode"
+#endif
         fft.update();
         for (auto i = 0u; i < display.WIDTH; i++) {
-            uint16_t sample = std::min((int16_t)(display.HEIGHT * 255), (int16_t)fft.get_scaled_fix15(i + FFT_SKIP_BINS, loudness_adjust[i]));
+            fix15 sample = std::min(float_to_fix15(max_sample_from_fft), fft.get_scaled_as_fix15(i + FFT_SKIP_BINS, loudness_adjust[i]));
             uint8_t maxy = 0;
 
             for (int j = 0; j < HISTORY_LEN; ++j) {
@@ -263,20 +279,31 @@ static void btstack_audio_pico_sink_fill_buffers(void){
                 }
             }
 
+#ifdef SCALE_SQRT
+            fix15 subtract = subtract_step;
+#endif
             for (auto y = 0; y < display.HEIGHT; y++) {
                 uint8_t r = 0;
                 uint8_t g = 0;
                 uint8_t b = 0;
-                if (sample > 255) {
+                if (sample > int_to_fix15(lower_threshold)) {
                     r = (uint16_t)(palette_main[i].r);
                     g = (uint16_t)(palette_main[i].g);
                     b = (uint16_t)(palette_main[i].b);
-                    sample -= 255;
+#ifdef SCALE_LOGARITHMIC
+                    sample = multiply_fix15_unit(multiple, sample);
+#else 
+                    sample = std::max(1, sample - subtract);
+#ifdef SCALE_SQRT
+                    subtract += subtract_step;
+#endif
+#endif
                 }
                 else if (sample > 0) {
-                    r = std::min((uint16_t)(palette_main[i].r), sample);
-                    g = std::min((uint16_t)(palette_main[i].g), sample);
-                    b = std::min((uint16_t)(palette_main[i].b), sample);
+                    uint16_t int_sample = (uint16_t)fix15_to_int(sample);
+                    r = std::min((uint16_t)(palette_main[i].r), int_sample);
+                    g = std::min((uint16_t)(palette_main[i].g), int_sample);
+                    b = std::min((uint16_t)(palette_main[i].b), int_sample);
                     eq_history[i][history_idx] = y;
                     sample = 0;
                     if (maxy < y) {

src/fixed_fft.cpp

@@ -28,6 +28,10 @@ int FIX_FFT::get_scaled_fix15(unsigned int i, fix15 scale) {
     return fix15_to_int(multiply_fix15(fr[i], scale));
 }
 
+int FIX_FFT::get_scaled_as_fix15(unsigned int i, fix15 scale) {
+    return multiply_fix15(fr[i], scale);
+}
+
 void FIX_FFT::init() {
 
     // Populate Filter and Sine tables
@@ -75,13 +79,6 @@ float FIX_FFT::max_frequency() {
     return max_freq_dex * (sample_rate / SAMPLE_COUNT);
 }
 
-// abs(a) must be <= 1
-constexpr __always_inline fix15 multiply_fix15_unit(fix15 a, fix15 b) {
-    int32_t bh = b >> 15;
-    int32_t bl = b & 0x7fff;
-    return ((a * bl) >> 15) + (a * bh);;
-}
-
 void FIX_FFT::FFT() {
     // Bit Reversal Permutation
     // Bit reversal code below originally based on that found here: 

src/fixed_fft.hpp

@@ -14,6 +14,13 @@ constexpr __always_inline float fix15_to_float(fix15 a) {return (float)(a) / 327
 constexpr __always_inline fix15 int_to_fix15(int a) {return (fix15)(a << 15);}
 constexpr __always_inline int fix15_to_int(fix15 a) {return (int)(a >> 15);}
 
+// abs(a) must be <= 1
+constexpr __always_inline fix15 multiply_fix15_unit(fix15 a, fix15 b) {
+    int32_t bh = b >> 15;
+    int32_t bl = b & 0x7fff;
+    return ((a * bl) >> 15) + (a * bh);;
+}
+
 constexpr unsigned int SAMPLE_COUNT = 1024u;
 
 class FIX_FFT {
@@ -56,4 +63,5 @@ class FIX_FFT {
         float max_frequency();
         int get_scaled(unsigned int i, unsigned int scale);
         int get_scaled_fix15(unsigned int i, fix15 scale);
+        fix15 get_scaled_as_fix15(unsigned int i, fix15 scale);
 };