HUB75 cleanup, double buffer improvement

* code cleanup, removing some unneeded sanity checks
* use dirty bits in double buffer mode, too -> only not-black pixels are drawn into the back-buffer (20%-30% faster)

wled00/bus_manager.cpp

@@ -19,7 +19,7 @@ bool getBitFromArray(const uint8_t* byteArray, size_t position) { // get bit val
 }
 
 void setBitInArray(uint8_t* byteArray, size_t position, bool value) {  // set bit - with error handling for nullptr
-    if (byteArray == nullptr) return;
+    //if (byteArray == nullptr) return;
     size_t byteIndex = position / 8;
     unsigned bitIndex = position % 8;
     if (value)
@@ -526,7 +526,6 @@ BusHub75Matrix::BusHub75Matrix(BusConfig &bc) : Bus(bc.type, bc.start, bc.autoWh
 
   _valid = false;
   mxconfig.double_buff = false; // default to off, known to cause issue with some effects but needs more memory
-  isBlack = false;
 
   fourScanPanel = nullptr;
 
@@ -700,14 +699,20 @@ BusHub75Matrix::BusHub75Matrix(BusConfig &bc) : Bus(bc.type, bc.start, bc.autoWh
 
     if (_ledBuffer) free(_ledBuffer);                 // should not happen
     if (_ledsDirty) free(_ledsDirty);                 // should not happen
-    if(mxconfig.double_buff == false) {
-      _ledBuffer = (CRGB*) calloc(_len, sizeof(CRGB));  // create LEDs buffer (initialized to BLACK)
-      _ledsDirty = (byte*) malloc(getBitArrayBytes(_len));  // create LEDs dirty bits
-      //_ledsDirty = nullptr;
-      setBitArray(_ledsDirty, _len, false);             // reset dirty bits
+    _ledsDirty = (byte*) malloc(getBitArrayBytes(_len));  // create LEDs dirty bits
+
+    if (_ledsDirty == nullptr) {
+      display->stopDMAoutput();
+      delete display; display = nullptr;
+      _valid = false;
+      USER_PRINTLN(F("MatrixPanel_I2S_DMA not started - not enough memory for dirty bits!"));
+      return;  //  fail is we cannot get memory for the buffer
     }
+    setBitArray(_ledsDirty, _len, false);             // reset dirty bits
 
-    isBlack = true;
+    if (mxconfig.double_buff == false) {
+      _ledBuffer = (CRGB*) calloc(_len, sizeof(CRGB));  // create LEDs buffer (initialized to BLACK)
+    }
   }
 
   switch(bc.type) {
@@ -753,11 +758,12 @@ void __attribute__((hot)) BusHub75Matrix::setPixelColor(uint16_t pix, uint32_t c
     if (_ledBuffer[pix] != fastled_col) {
       _ledBuffer[pix] = fastled_col;
       setBitInArray(_ledsDirty, pix, true);  // flag pixel as "dirty"
-      isBlack = false;
     }
   }
   else {
-    if (isBlack && (c == BLACK)) return;  // reject black pixels directly after clearScreen()
+    if ((c == BLACK) && (getBitFromArray(_ledsDirty, pix) == false)) return; // ignore black if pixel is already black
+    setBitInArray(_ledsDirty, pix, c != BLACK);                              // dirty = true means "color is not BLACK"
+
     #ifndef NO_CIE1931
     c = unGamma24(c); // to use the driver linear brightness feature, we first need to undo WLED gamma correction
     #endif
@@ -776,7 +782,6 @@ void __attribute__((hot)) BusHub75Matrix::setPixelColor(uint16_t pix, uint32_t c
       int y = pix / width;
       display->drawPixelRGB888(int16_t(x), int16_t(y), r, g, b);
     }
-    isBlack = false;
   }
 }
 
@@ -785,7 +790,7 @@ uint32_t BusHub75Matrix::getPixelColor(uint16_t pix) const {
   if (_ledBuffer)
     return uint32_t(_ledBuffer[pix].scale8(_bri)) & 0x00FFFFFF;  // scale8() is needed to mimic NeoPixelBus, which returns scaled-down colours
   else
-    return BLACK;
+    return getBitFromArray(_ledsDirty, pix) ? DARKGREY: BLACK;   // just a hack - we only know if the pixel is black or not
 }
 
 void BusHub75Matrix::setBrightness(uint8_t b, bool immediate) {
@@ -797,7 +802,6 @@ void __attribute__((hot)) BusHub75Matrix::show(void) {
   if (!_valid) return;
   if (_ledBuffer) {
     // write out buffered LEDs
-    bool haveDirtyBits = (_ledsDirty != nullptr);
     bool isFourScan = (fourScanPanel != nullptr);
     unsigned width  = isFourScan ? fourScanPanel->width()  : display->width();
     unsigned height = isFourScan ? fourScanPanel->height() : display->height();
@@ -806,7 +810,7 @@ void __attribute__((hot)) BusHub75Matrix::show(void) {
 
     size_t pix = 0; // running pixel index
     for (int y=0; y<height; y++) for (int x=0; x<width; x++) {
-      if ( !haveDirtyBits || (getBitFromArray(_ledsDirty, pix) == true)) {  // only repaint the "dirty"  pixels
+      if (getBitFromArray(_ledsDirty, pix) == true) {        // only repaint the "dirty"  pixels
         uint32_t c = uint32_t(_ledBuffer[pix]) & 0x00FFFFFF; // get RGB color, removing FastLED "alpha" component 
         #ifndef NO_CIE1931
         c = unGamma24(c); // to use the driver linear brightness feature, we first need to undo WLED gamma correction
@@ -819,14 +823,14 @@ void __attribute__((hot)) BusHub75Matrix::show(void) {
       }
       pix ++;
     }
-    if (haveDirtyBits) setBitArray(_ledsDirty, _len, false);  // reset dirty bits
+    setBitArray(_ledsDirty, _len, false);  // buffer shown - reset all dirty bits
   }
 
   if(mxconfig.double_buff) {
     display->flipDMABuffer(); // Show the back buffer, set current output buffer to the back (i.e. no longer being sent to LED panels)
     // while(!previousBufferFree) delay(1);   // experimental - Wait before we allow any writing to the buffer. Stop flicker.
     display->clearScreen();   // Now clear the back-buffer
-    isBlack = true;
+    setBitArray(_ledsDirty, _len, false);  // dislay buffer is blank - reset all dirty bits
   }
 }
 
@@ -840,7 +844,6 @@ void BusHub75Matrix::cleanup() {
   delete display;
   display = nullptr;
   fourScanPanel = nullptr;
-  isBlack = false;
   if (_ledBuffer != nullptr) free(_ledBuffer); _ledBuffer = nullptr;
   if (_ledsDirty != nullptr) free(_ledsDirty); _ledsDirty = nullptr;      
 }

wled00/bus_manager.h

@@ -389,7 +389,6 @@ class BusHub75Matrix : public Bus {
     MatrixPanel_I2S_DMA *display = nullptr;
     VirtualMatrixPanel  *fourScanPanel = nullptr;
     HUB75_I2S_CFG mxconfig;
-    bool isBlack = false;
     CRGB *_ledBuffer = nullptr;
     byte *_ledsDirty = nullptr;
 };