godot-demo-projects/2d/screen_space_shaders/shaders/mirage.shader

shader_type canvas_item;

uniform float frequency = 60;
uniform float depth = 0.005;

void fragment() {
	vec2 uv = SCREEN_UV;
	uv.x += sin(uv.y * frequency + TIME) * depth;
	uv.x = clamp(uv.x, 0.0, 1.0);
	vec3 c = textureLod(SCREEN_TEXTURE, uv, 0.0).rgb;

	COLOR.rgb = c;
}