fix particle brightness distribution with new gamma correction (#4710)

Particle System depends on linear brightness distribution, gamma corrected values are non-linear.
- added invers gamma table
- reversing gamma after brightness distribution makes it linear once again

wled00/FXparticleSystem.cpp

@@ -584,7 +584,7 @@ void ParticleSystem2D::render() {
       continue;
     // generate RGB values for particle
     if (fireIntesity) { // fire mode
-      brightness = (uint32_t)particles[i].ttl * (3 + (fireIntesity >> 5)) + 20;
+      brightness = (uint32_t)particles[i].ttl * (3 + (fireIntesity >> 5)) + 5;
       brightness = min(brightness, (uint32_t)255);
       baseRGB = ColorFromPaletteWLED(SEGPALETTE, brightness, 255, LINEARBLEND_NOWRAP);
     }
@@ -600,6 +600,7 @@ void ParticleSystem2D::render() {
         baseRGB = (CRGB)tempcolor;
       }
     }
+    brightness = gamma8(brightness); // apply gamma correction, used for gamma-inverted brightness distribution
     renderParticle(i, brightness, baseRGB, particlesettings.wrapX, particlesettings.wrapY);
   }
 
@@ -676,6 +677,14 @@ __attribute__((optimize("O2"))) void ParticleSystem2D::renderParticle(const uint
   pxlbrightness[1] = (dx * precal2) >> PS_P_SURFACE; // bottom right value equal to (dx * (PS_P_RADIUS-dy) * brightness) >> PS_P_SURFACE
   pxlbrightness[2] = (dx * precal3) >> PS_P_SURFACE; // top right value equal to (dx * dy * brightness) >> PS_P_SURFACE
   pxlbrightness[3] = (precal1 * precal3) >> PS_P_SURFACE; // top left value equal to ((PS_P_RADIUS-dx) * dy * brightness) >> PS_P_SURFACE
+  // adjust brightness such that distribution is linear after gamma correction:
+  // - scale brigthness with gamma correction (done in render())
+  // - apply inverse gamma correction to brightness values
+  // - gamma is applied again in show() -> the resulting brightness distribution is linear but gamma corrected in total
+  pxlbrightness[0] = gamma8inv(pxlbrightness[0]); // use look-up-table for invers gamma
+  pxlbrightness[1] = gamma8inv(pxlbrightness[1]);
+  pxlbrightness[2] = gamma8inv(pxlbrightness[2]);
+  pxlbrightness[3] = gamma8inv(pxlbrightness[3]);
 
   if (advPartProps && advPartProps[particleindex].size > 1) { //render particle to a bigger size
     CRGB renderbuffer[100]; // 10x10 pixel buffer
@@ -1467,6 +1476,7 @@ void ParticleSystem1D::render() {
         baseRGB = (CRGB)tempcolor;
       }
     }
+    brightness = gamma8(brightness); // apply gamma correction, used for gamma-inverted brightness distribution
     renderParticle(i, brightness, baseRGB, particlesettings.wrap);
   }
   // apply smear-blur to rendered frame
@@ -1534,6 +1544,12 @@ __attribute__((optimize("O2"))) void ParticleSystem1D::renderParticle(const uint
   //calculate the brightness values for both pixels using linear interpolation (note: in standard rendering out of frame pixels could be skipped but if checks add more clock cycles over all)
   pxlbrightness[0] = (((int32_t)PS_P_RADIUS_1D - dx) * brightness) >> PS_P_SURFACE_1D;
   pxlbrightness[1] = (dx * brightness) >> PS_P_SURFACE_1D;
+  // adjust brightness such that distribution is linear after gamma correction:
+  // - scale brigthness with gamma correction (done in render())
+  // - apply inverse gamma correction to brightness values
+  // - gamma is applied again in show() -> the resulting brightness distribution is linear but gamma corrected in total
+  pxlbrightness[0] = gamma8inv(pxlbrightness[0]); // use look-up-table for invers gamma
+  pxlbrightness[1] = gamma8inv(pxlbrightness[1]);
 
   // check if particle has advanced size properties and buffer is available
   if (advPartProps && advPartProps[particleindex].size > 1) {

wled00/cfg.cpp

@@ -532,7 +532,7 @@ bool deserializeConfig(JsonObject doc, bool fromFS) {
     gammaCorrectBri = false;
     gammaCorrectCol = false;
   }
-  NeoGammaWLEDMethod::calcGammaTable(gammaCorrectVal); // fill look-up table
+  NeoGammaWLEDMethod::calcGammaTable(gammaCorrectVal); // fill look-up tables
 
   JsonObject light_tr = light["tr"];
   int tdd = light_tr["dur"] | -1;

wled00/colors.cpp

@@ -564,14 +564,17 @@ uint16_t approximateKelvinFromRGB(uint32_t rgb) {
   }
 }
 
-// gamma lookup table used for color correction (filled on 1st use (cfg.cpp & set.cpp))
+// gamma lookup tables used for color correction (filled on 1st use (cfg.cpp & set.cpp))
 uint8_t NeoGammaWLEDMethod::gammaT[256];
+uint8_t NeoGammaWLEDMethod::gammaT_inv[256];
 
-// re-calculates & fills gamma table
+// re-calculates & fills gamma tables
 void NeoGammaWLEDMethod::calcGammaTable(float gamma)
 {
+  float gamma_inv = 1.0f / gamma; // inverse gamma
   for (size_t i = 0; i < 256; i++) {
     gammaT[i] = (int)(powf((float)i / 255.0f, gamma) * 255.0f + 0.5f);
+    gammaT_inv[i] = (int)(powf((float)i / 255.0f, gamma_inv) * 255.0f + 0.5f);
   }
 }
 

wled00/fcn_declare.h

@@ -158,13 +158,16 @@ class NeoGammaWLEDMethod {
   public:
     [[gnu::hot]] static uint8_t Correct(uint8_t value);         // apply Gamma to single channel
     [[gnu::hot]] static uint32_t Correct32(uint32_t color);     // apply Gamma to RGBW32 color (WLED specific, not used by NPB)
-    static void calcGammaTable(float gamma);                              // re-calculates & fills gamma table
+    static void calcGammaTable(float gamma);                    // re-calculates & fills gamma tables
     static inline uint8_t rawGamma8(uint8_t val) { return gammaT[val]; }  // get value from Gamma table (WLED specific, not used by NPB)
+    static inline uint8_t rawInverseGamma8(uint8_t val) { return gammaT_inv[val]; }  // get value from inverse Gamma table (WLED specific, not used by NPB)
   private:
     static uint8_t gammaT[];
+    static uint8_t gammaT_inv[];
 };
 #define gamma32(c) NeoGammaWLEDMethod::Correct32(c)
 #define gamma8(c)  NeoGammaWLEDMethod::rawGamma8(c)
+#define gamma8inv(c)  NeoGammaWLEDMethod::rawInverseGamma8(c)
 [[gnu::hot, gnu::pure]] uint32_t color_blend(uint32_t c1, uint32_t c2 , uint8_t blend);
 inline uint32_t color_blend16(uint32_t c1, uint32_t c2, uint16_t b) { return color_blend(c1, c2, b >> 8); };
 [[gnu::hot, gnu::pure]] uint32_t color_add(uint32_t, uint32_t, bool preserveCR = false);

wled00/set.cpp

@@ -341,7 +341,7 @@ void handleSettingsSet(AsyncWebServerRequest *request, byte subPage)
       gammaCorrectBri = false;
       gammaCorrectCol = false;
     }
-    NeoGammaWLEDMethod::calcGammaTable(gammaCorrectVal); // fill look-up table
+    NeoGammaWLEDMethod::calcGammaTable(gammaCorrectVal); // fill look-up tables
 
     t = request->arg(F("TD")).toInt();
     if (t >= 0) transitionDelayDefault = t;