feat: add seal.

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

@@ -0,0 +1,13 @@
+float ao = smoothstep(0.0, 0.7, vGrassUv.y);
+ao = mix(0.05, 1.0, ao);
+
+vec3 rootColor = diffuseColor.rgb * 0.4;
+vec3 tipColor = diffuseColor.rgb * 1.5;
+
+vec3 grassColor = mix(rootColor, tipColor, vGrassUv.y);
+grassColor *= ao;
+
+float translucency = pow(vGrassUv.y, 2.0) * 0.5;
+grassColor += diffuseColor.rgb * translucency;
+
+diffuseColor.rgb = grassColor;