+
+ "float eval_zero( vec2 uv )"
+ "{"
+ "vec4 vsines = sin( (uTime+uv.y*80.0) * vec4(1.1,2.0234,3.73,2.444) );"
+ "float gradient = min( uv.y, 0.0 );"
+ "float offset = vsines.x*vsines.y*vsines.z*vsines.w*gradient;"
+
+ "vec2 vpos = uv + vec2( offset, 0.0 );"
+ "float dist = dot( vpos, vpos );"
+
+ "float fring = step(0.1*0.1,dist) * step(dist,0.15*0.15);"
+ "return max( 0.0, fring * 1.0+gradient*6.0 );"
+ "}"