fix: #410, but on windows. Committing to try in linux and OSX.

Author: Robert Plummer

src/backend/web-gl/fragment-shader.js

@@ -204,22 +204,57 @@ float decode8(vec4 texel, int index) {
   return 0.0;
 }
 
-vec4 encode32(float f) {
+vec4 oldEncode32(float f) {
   float F = abs(f);
-  float sign = f < 0.0 ? 1.0 : 0.0;
-  float exponent = floor(log2(F));
-  float mantissa = (exp2(-exponent) * F);
+  float sign = step(0.0, -f);
+  float exponent = floor(log2(f));
+  float mantissa = f * pow(2.0, -exponent) - 1.0;
   // exponent += floor(log2(mantissa));
+  exponent = exponent + 127.0;
   vec4 texel = vec4(F * exp2(23.0-exponent)) * SCALE_FACTOR_INV;
   texel.rg = integerMod(texel.rg, 256.0);
   texel.b = integerMod(texel.b, 128.0);
   texel.a = exponent*0.5 + 63.5;
-  texel.ba += vec2(integerMod(exponent+127.0, 2.0), sign) * 128.0;
+  texel.ba += vec2(integerMod(exponent, 2.0), sign) * 128.0;
   texel = floor(texel);
   texel *= 0.003921569; // 1/255
   __ENCODE32_ENDIANNESS__;
   return texel;
 }
+
+// Borrowed from exellect info here: http://www.vizitsolutions.com/portfolio/webgl/gpgpu/speedBumps.html
+// http://www.vizitsolutions.com/portfolio/webgl/gpgpu/js/ToUnsignedBytes.js
+vec4 encode32(float value) {
+  if (value == 0.0) return vec4(0, 0, 0, 0);
+
+  float exponent;
+  float mantissa;
+  vec4  result;
+  float sgn;
+
+  sgn = step(0.0, -value);
+  value = abs(value);
+
+  exponent = floor(log2(value));
+
+  mantissa = value*pow(2.0, -exponent)-1.0;
+  exponent = exponent+127.0;
+  result   = vec4(0,0,0,0);
+
+  result.a = floor(exponent/2.0);
+  exponent = exponent - result.a*2.0;
+  result.a = result.a + 128.0*sgn;
+
+  result.b = floor(mantissa * 128.0);
+  mantissa = mantissa - result.b / 128.0;
+  result.b = result.b + exponent*128.0;
+
+  result.g = floor(mantissa*32768.0);
+  mantissa = mantissa - result.g/32768.0;
+
+  result.r = floor(mantissa*8388608.0);
+  return result/255.0;
+}
 // Dragons end here
 
 int index;