fix directionalLight direction sense

Author: Spongman

src/webgl/shaders/light.vert

@@ -50,7 +50,7 @@ void main(void){
   for (int j = 0; j < 8; j++) {
     if (uDirectionalLightCount == j) break;
     vec3 dir = uLightingDirection[j];
-    float directionalLightWeighting = max(dot(vertexNormal, dir), 0.0);
+    float directionalLightWeighting = max(dot(vertexNormal, -dir), 0.0);
     directionalLightFactor += uDirectionalColor[j] * directionalLightWeighting;
   }
 

src/webgl/shaders/phong.frag

@@ -46,7 +46,7 @@ float phongSpecular(
 float lambertDiffuse(
   vec3 lightDirection,
   vec3 surfaceNormal) {
-  return max(0.0, dot(lightDirection, surfaceNormal));
+  return max(0.0, dot(-lightDirection, surfaceNormal));
 }
 
 LightResult light(vec3 lightVector) {