Add Hue Spectrum Example

and to elaborate how the BCM correction works

examples/HueValueSpectrumTestDemo/HueValueSpectrumTestDemo.ino

@@ -0,0 +1,71 @@
+#define PANEL_RES_X 64    // Number of pixels wide of each INDIVIDUAL panel module. 
+#define PANEL_RES_Y 32     // Number of pixels tall of each INDIVIDUAL panel module.
+#define PANEL_CHAIN 1      // Total number of panels chained one to another
+
+#define NO_CIE1931
+#define PIXEL_COLOUR_DEPTH_BITS      8
+#include <ESP32-HUB75-MatrixPanel-I2S-DMA.h>
+
+MatrixPanel_I2S_DMA *dma_display = nullptr;
+
+#define R1_PIN 25
+#define G1_PIN 26
+#define B1_PIN 27
+#define R2_PIN 14
+#define G2_PIN 12
+#define B2_PIN 13
+#define A_PIN 23
+#define B_PIN 19
+#define C_PIN 5
+#define D_PIN 17
+#define E_PIN -1 // required for 1/32 scan panels, esp for 64x64 or 128x64 displays
+#define LAT_PIN 4
+#define OE_PIN 15
+#define CLK_PIN 16
+
+uint32_t lastMillis;
+
+void setup() {
+  HUB75_I2S_CFG::i2s_pins _pins={R1_PIN, G1_PIN, B1_PIN, R2_PIN, G2_PIN, B2_PIN, A_PIN, B_PIN, C_PIN, D_PIN, E_PIN, LAT_PIN, OE_PIN, CLK_PIN};
+  HUB75_I2S_CFG mxconfig(
+    PANEL_RES_X, // Module width
+    PANEL_RES_Y, // Module height
+    1, // chain length
+    _pins // pin mapping
+  );
+  //mxconfig.gpio.e = 18;
+  //mxconfig.clkphase = false;
+  //mxconfig.driver = HUB75_I2S_CFG::FM6126A;
+
+  // Display Setup
+  dma_display = new MatrixPanel_I2S_DMA(mxconfig);
+  dma_display->begin();
+  dma_display->clearScreen();
+}
+
+void loop() {
+  // Canvas loop
+  float t = (float)(millis()%4000)/4000.f;
+  for(int x = 0; x < PANEL_RES_X; x++){
+    float r =max(min(cosf(2.f*PI*(t+(float)x/PANEL_RES_X+0.f/3.f))+0.5f,1.f),0.f);
+    float g =max(min(cosf(2.f*PI*(t+(float)x/PANEL_RES_X+1.f/3.f))+0.5f,1.f),0.f);
+    float b =max(min(cosf(2.f*PI*(t+(float)x/PANEL_RES_X+2.f/3.f))+0.5f,1.f),0.f);
+    for(int y = 0; y < PANEL_RES_Y; y++)
+      if(y*2 < PANEL_RES_Y){
+        float t = (2.f*y)/PANEL_RES_Y;
+        dma_display->drawPixelRGB888(x,y,
+          (r*t)*255,
+          (g*t)*255,
+          (b*t)*255
+        );
+      }else{
+        float t = (2.f*(PANEL_RES_Y-y))/PANEL_RES_Y;
+        dma_display->drawPixelRGB888(x,y,
+          (r*t+1-t)*255,
+          (g*t+1-t)*255,
+          (b*t+1-t)*255
+        );
+      }
+        
+  }
+}

src/ESP32-HUB75-MatrixPanel-I2S-DMA.cpp

@@ -705,7 +705,20 @@ void MatrixPanel_I2S_DMA::brtCtrlOEv2(uint8_t brt, const int _buff_id) {
     // let's set OE control bits for specific pixels in each color_index subrows
     uint8_t colouridx = dma_buff.rowBits[row_idx]->colour_depth;
     do {
-        int brightness_in_x_pixels = PIXELS_PER_ROW * brt >> 8 + max( ( dma_buff.rowBits[row_idx]->colour_depth - colouridx - 2 ), 0);
+      //   Multiply brightness according to index of bitplane (color index subrow)
+      // in respect of accumulating LED intensities with Binary-Coded Modulation:
+      // bitplane 0 is 1/1 of total brightness; bitplane 1 is 1/2; bitplane 2 is 1/4, etc
+      // accumulating all of them together means we will get only ~1/4 of the total brightness.
+
+      //   During the DMA, assume bitplane 0 shown for 4 subrows; bitplane 1 shown for 2 subrows;
+      // bitplane 2 and the rest shown for one subrow, would give us ~2/3 of the total brightness,
+      // which is good balance for the depth, brightness, while the flickers still less noticeable:
+      //                 row 0        (blanking)\   row 1        (blanking)\   row 2        (blanking)\   ..
+      // bitplane  : ... 0 0 0 0 1 1 2 3 4 5 6 7 \- 0 0 0 0 1 1 2 3 4 5 6 7 \- 0 0 0 0 1 1 2 3 4 5 6 7 \- ..
+      // rightshift: ... 0 0 0 0 0 0 0 1 2 3 4 5 -\ 0 0 0 0 0 0 0 1 2 3 4 5 -\ 0 0 0 0 0 0 0 1 2 3 4 5 -\ ..
+      char bitplane   = dma_buff.rowBits[row_idx]->colour_depth-colouridx;
+      char rightshift = std::max(bitplane-2,0);
+      int brightness_in_x_pixels = PIXELS_PER_ROW * brt >> 8 + rightshift;
       --colouridx;
 
       // switch pointer to a row for a specific color index