Doom Screen Melt Effect

A version of the Screen melt effect from Doom that plays as you start a level.

Values do need to be set by an outside script for the shader to work correctly.

This example code I used to achieve a similar effect to Doom. Creating a duplicate texture of the screen to overlay as menus swap, then melting away that duplicate texture with this shader.

extends ColorRect

var melting := false
var timer := 0.0 //Incremented by melt_speed then applied to the timer variable in the shader

@export var x_resolution := 100.0 //Value must be greater or equal to y_offsets.length() in the shader
@export var max_offset := 2.0
@export var melt_speed := 0.02


# Called when the node enters the scene tree for the first time.
func _ready():
	hide()


# Called every frame. 'delta' is the elapsed time since the previous frame.
func _process(_delta):
	if melting:
		timer += melt_speed
		self.material.set_shader_parameter("timer", timer)
	elif Input.is_action_just_pressed("Dev_Log"):
		generate_offsets()

# Call this before transitioning, creates a copy of the screen texture so changes
# can be made underneath before melting to show the new screen.
func generate_offsets():
	var offsets = []
	for i in x_resolution:
		offsets.append(randf_range(1.0, max_offset))
	self.material.set_shader_parameter("y_offsets", offsets)
	
	var img = get_viewport().get_texture().get_image()
	var tex = ImageTexture.create_from_image(img)
	self.material.set_shader_parameter("melt_tex", tex)
	
	show()

# Call this after generate_offsets
func transition():
	self.material.set_shader_parameter("melting", true)
	melting = true

Shader code

shader_type canvas_item;

//Incremented by outside script to move effect
uniform float timer = 0.0; 

//Array size determines how many vertical strips appear
uniform float[64] y_offsets; 

//Texture to melt away, example above uses a duplicate screen texture as a transition
uniform sampler2D melt_tex; 

//Controls whether the effect can play
uniform bool melting = false;

void fragment() {
	vec2 tex_uv = SCREEN_UV;
	if (melting)
	{
		float index = tex_uv.x * float(y_offsets.length());
		tex_uv.y -= timer * y_offsets[int(index)];
		
		if (tex_uv.y < 0.0 || tex_uv.y > 1.0) discard;
	}
	
	COLOR = texture(melt_tex, tex_uv);
}

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