I waste several hours

core/assets/shaders/fog.frag

@@ -0,0 +1,12 @@
+#define HIGHP
+#define QUANT 0.3
+
+uniform sampler2D u_texture;
+
+varying vec4 v_color;
+varying vec2 v_texCoords;
+
+void main(){
+    vec4 color = texture2D(u_texture, v_texCoords.xy);
+    gl_FragColor = vec4(0.0, 0.0, 0.0, 1.0 - floor(color.r / QUANT) * QUANT);
+}