feat: overhaul grass

src/app/niko/scene-components/shaders/grass.vert

@@ -21,22 +21,32 @@ float spring = sin(uTime * 2.0 + phase) * 0.06 + sin(uTime * 4.5 + phase * 1.5)
 float angleNoise = fbm(windSamplePos * 2.0 + uTime * 0.1) - 0.5;
 vec2 windDir = normalize(mainWindDir + vec2(-mainWindDir.y, mainWindDir.x) * angleNoise * 0.4);
 
-float taperFactor = pow(uv.y, 4.0);
-float taper = 1.0 - taperFactor * 0.6;
+// taper (fade)
+float taperFactor = uv.y * uv.y * uv.y;
+float taper = 1.0 - taperFactor * 0.85;
 transformed.x *= taper;
 transformed.z *= taper;
 
+// curve
 float curveVal = fbm(vec2(gx, gz) * 0.5);
-float curveStrength = 2.0 + curveVal * 2.0; 
+float curveStrength = 1.5 + curveVal * 2.5; 
 float curveAmount = uv.y * uv.y * curveStrength; 
 vec2 curveDir = normalize(vec2(curveVal, fbm(vec2(gz, gx))) - 0.5);
-transformed.x += curveAmount * curveDir.x * 0.5;
-transformed.z += curveAmount * curveDir.y * 0.5;
+transformed.x += curveAmount * curveDir.x * 0.4;
+transformed.z += curveAmount * curveDir.y * 0.4;
 
+// sway
 float swayAmount = (totalWind + spring) * uv.y * uv.y;
 transformed.x += swayAmount * windDir.x;
 transformed.z += swayAmount * windDir.y;
 transformed.y -= abs(swayAmount) * 0.2;
 
-objectNormal = vec3(0.0, 1.0, 0.0); 
+// normal comp
+vec2 totalBend = curveDir * curveAmount * 0.4 + windDir * swayAmount;
+float bendMag = length(totalBend);
+vec3 bentNormal = normalize(vec3(-totalBend.x * 0.5, 1.0, -totalBend.y * 0.5));
+
+// normal mix
+objectNormal = normalize(mix(vec3(0.0, 1.0, 0.0), bentNormal, uv.y));
+
 vWorldPos = (modelMatrix * instanceMatrix * vec4(transformed, 1.0)).xyz;