blur speedup

it seems that SEGMENT.blur() is the main bottleneck for many 2D effects.

This change optimizes performance of the function:
* avoid to re-write unchanged pixels
* early exit when blur_amount == 0 (=nothing to do)
* use _fast_ types where possible

I've seen up to 20% speedup with this change.

wled00/FX_2Dfcn.cpp

@@ -306,6 +306,7 @@ void Segment::blendPixelColorXY(uint16_t x, uint16_t y, uint32_t color, uint8_t
 
 // Adds the specified color with the existing pixel color perserving color balance.
 void Segment::addPixelColorXY(int x, int y, uint32_t color, bool fast) {
+  if (x >= virtualWidth() || y >= virtualHeight() || x<0 || y<0) return;  // if pixel would fall out of virtual segment just exit
   uint32_t col = getPixelColorXY(x,y);
   uint8_t r = R(col);
   uint8_t g = G(col);
@@ -330,50 +331,54 @@ void Segment::fadePixelColorXY(uint16_t x, uint16_t y, uint8_t fade) {
 
 // blurRow: perform a blur on a row of a rectangular matrix
 void Segment::blurRow(uint16_t row, fract8 blur_amount) {
-  const uint16_t cols = virtualWidth();
-  const uint16_t rows = virtualHeight();
+  const uint_fast16_t cols = virtualWidth();
+  const uint_fast16_t rows = virtualHeight();
 
   if (row >= rows) return;
   // blur one row
   uint8_t keep = 255 - blur_amount;
   uint8_t seep = blur_amount >> 1;
   CRGB carryover = CRGB::Black;
-  for (uint16_t x = 0; x < cols; x++) {
+  for (uint_fast16_t x = 0; x < cols; x++) {
     CRGB cur = getPixelColorXY(x, row);
+    uint32_t before = uint32_t(cur);     // remember color before blur
     CRGB part = cur;
     part.nscale8(seep);
     cur.nscale8(keep);
     cur += carryover;
-    if (x) {
+    if (x>0) {
       CRGB prev = CRGB(getPixelColorXY(x-1, row)) + part;
       setPixelColorXY(x-1, row, prev);
     }
-    setPixelColorXY(x, row, cur);
+    if (before != uint32_t(cur))         // optimization: only set pixel if color has changed
+      setPixelColorXY(x, row, cur);
     carryover = part;
   }
 }
 
 // blurCol: perform a blur on a column of a rectangular matrix
 void Segment::blurCol(uint16_t col, fract8 blur_amount) {
-  const uint16_t cols = virtualWidth();
-  const uint16_t rows = virtualHeight();
+  const uint_fast16_t cols = virtualWidth();
+  const uint_fast16_t rows = virtualHeight();
 
   if (col >= cols) return;
   // blur one column
   uint8_t keep = 255 - blur_amount;
   uint8_t seep = blur_amount >> 1;
   CRGB carryover = CRGB::Black;
-  for (uint16_t i = 0; i < rows; i++) {
-    CRGB cur = getPixelColorXY(col, i);
+  for (uint_fast16_t y = 0; y < rows; y++) {
+    CRGB cur = getPixelColorXY(col, y);
     CRGB part = cur;
+    uint32_t before = uint32_t(cur);     // remember color before blur
     part.nscale8(seep);
     cur.nscale8(keep);
     cur += carryover;
-    if (i) {
-      CRGB prev = CRGB(getPixelColorXY(col, i-1)) + part;
-      setPixelColorXY(col, i-1, prev);
+    if (y>0) {
+      CRGB prev = CRGB(getPixelColorXY(col, y-1)) + part;
+      setPixelColorXY(col, y-1, prev);
     }
-    setPixelColorXY(col, i, cur);
+    if (before != uint32_t(cur))         // optimization: only set pixel if color has changed
+      setPixelColorXY(col, y, cur);
     carryover = part;
   }
 }
@@ -392,8 +397,8 @@ void Segment::box_blur(uint16_t i, bool vertical, fract8 blur_amount) {
   for (uint16_t j = 0; j < dim1; j++) {
     uint16_t x = vertical ? i : j;
     uint16_t y = vertical ? j : i;
-    uint16_t xp = vertical ? x : x-1;
-    uint16_t yp = vertical ? y-1 : y;
+    int16_t xp = vertical ? x : x-1;  // "signed" to prevent underflow
+    int16_t yp = vertical ? y-1 : y;  // "signed" to prevent underflow
     uint16_t xn = vertical ? x : x+1;
     uint16_t yn = vertical ? y+1 : y;
     CRGB curr = getPixelColorXY(x,y);

wled00/FX_fcn.cpp

@@ -887,6 +887,7 @@ void Segment::fade_out(uint8_t rate) {
 
 // fades all pixels to black using nscale8()
 void Segment::fadeToBlackBy(uint8_t fadeBy) {
+  if (fadeBy == 0) return;   // optimization - no scaling to apply
   const uint16_t cols = is2D() ? virtualWidth() : virtualLength();
   const uint16_t rows = virtualHeight(); // will be 1 for 1D
 
@@ -901,23 +902,26 @@ void Segment::fadeToBlackBy(uint8_t fadeBy) {
  */
 void Segment::blur(uint8_t blur_amount)
 {
+  if (blur_amount == 0) return; // optimization: 0 means "don't blur"
 #ifndef WLED_DISABLE_2D
   if (is2D()) {
     // compatibility with 2D
-    const uint16_t cols = virtualWidth();
-    const uint16_t rows = virtualHeight();
-    for (uint16_t i = 0; i < rows; i++) blurRow(i, blur_amount); // blur all rows
-    for (uint16_t k = 0; k < cols; k++) blurCol(k, blur_amount); // blur all columns
+    const uint_fast16_t cols = virtualWidth();
+    const uint_fast16_t rows = virtualHeight();
+    for (uint_fast16_t i = 0; i < rows; i++) blurRow(i, blur_amount); // blur all rows
+    for (uint_fast16_t k = 0; k < cols; k++) blurCol(k, blur_amount); // blur all columns
     return;
   }
 #endif
   uint8_t keep = 255 - blur_amount;
   uint8_t seep = blur_amount >> 1;
   CRGB carryover = CRGB::Black;
-  for(uint16_t i = 0; i < virtualLength(); i++)
+  uint_fast16_t vlength = virtualLength();
+  for(uint_fast16_t i = 0; i < vlength; i++)
   {
     CRGB cur = CRGB(getPixelColor(i));
     CRGB part = cur;
+    uint32_t before = uint32_t(cur); // remember color before blur
     part.nscale8(seep);
     cur.nscale8(keep);
     cur += carryover;
@@ -926,9 +930,10 @@ void Segment::blur(uint8_t blur_amount)
       uint8_t r = R(c);
       uint8_t g = G(c);
       uint8_t b = B(c);
-      setPixelColor(i-1, qadd8(r, part.red), qadd8(g, part.green), qadd8(b, part.blue));
+      setPixelColor((uint16_t)(i-1), qadd8(r, part.red), qadd8(g, part.green), qadd8(b, part.blue));
     }
-    setPixelColor(i,cur.red, cur.green, cur.blue);
+    if (before != uint32_t(cur))     // optimization: only set pixel if color has changed
+      setPixelColor((uint16_t)i,cur.red, cur.green, cur.blue);
     carryover = part;
   }
 }