implement gamma-correction

Author: Martin Schuhfuss

lib/ws281x-native.js

@@ -40,23 +40,45 @@ if(!ws281xNative) {
 }
 
 
+var gammaCorrect = (function() {
+    var _gamma = 2.8;
+    var _gammaTable = new Uint8Array(256);
 
-var _numLeds = 0,
-    _indexMapping = null;
+    for(var i=0; i<256; i++) {
+        _gammaTable[i] = Math.floor(Math.pow(i / 255, _gamma) * 255 + 0.5);
+    }
 
+    return function gammaCorrect(color) {
+        return (
+            _gammaTable[color & 0xff]
+            | (_gammaTable[(color >> 8) & 0xff] << 8)
+            | (_gammaTable[(color >> 16) & 0xff] << 16)
+        );
+    };
+} ());
 
-function remap(src, indexMapping) {
-    var dest = new Uint32Array(src.length);
 
-    for(var i=0; i<src.length; i++) {
-        dest[i] = src[indexMapping[i]];
-    }
+var remap = (function() {
+    var _tmpData = null;
 
-    return dest;
-}
+    return function remap(data, indexMapping) {
+        if(!_tmpData) {
+            _tmpData = new Uint32Array(data.length);
+        }
+
+        _tmpData.set(data);
+
+        for(var i=0; i<data.length; i++) {
+            data[i] = gammaCorrect(_tmpData[indexMapping[i]]);
+        }
+
+        return data;
+    };
+} ());
 
 
 var ws281x = new EventEmitter();
+var _indexMapping = null;
 
 /**
  * configures PWM and DMA for sending data to the LEDs
@@ -67,16 +89,14 @@ var ws281x = new EventEmitter();
  *                           (PWM frequency, DMA channel, GPIO, Brightness)
  */
 ws281x.init = function(numLeds, options) {
-    _numLeds = numLeds;
-
     ws281xNative.init(numLeds, options);
 };
 
 /**
  * register a mapping to manipulate array-indices within the
  * data-array before rendering.
  *
- * @param {Array.<Number>} map  the mapping, indexed by destination.
+ * @param {Array.<Number>} mapping  the mapping, indexed by destination.
  */
 ws281x.setIndexMapping = function(mapping) {
     _indexMapping = mapping;
@@ -96,6 +116,10 @@ ws281x.render = function(data) {
         data = remap(data, _indexMapping);
     }
 
+    for(var i=0; i<data.length; i++) {
+        data[i] = gammaCorrect(data[i]);
+    }
+
     ws281xNative.render(data);
     this.emit('render', data);