Interlaced Video

This shader simulates interlaced video combing.

For the set-up you will need:

– A ColorRect, set to full rect, with the Script below.

– A SubViewportContainer set to full rect and the property ‘Stretch‘ set to True. 

– A SubViewport, as a child of the container.

– A second Camera3D, as a child of the subviewport

– A Timer, set to ‘Autostart‘. 

If your camera is static that’s all you need, otherwise you will ned a RemoteTransform3D as a child of your player’s camera, with the target set to the Interlacing Camera.

Your node tree should look something like this.

TIPS:

– I recommend setting the interlacing timer to 0.01-0.025s for a 1-2 frame delay at 60fps. Longer times yield slightly better performance but look really bad.

– For better performance, set the “Stretch Shrink” property in your SubViewportContainer to 2. This will halve the combed picture’s resolution, It’s not too discernable and it’s significantly less expensive. (IMPORTANT: If you do this, set the ‘Modulate’ on the SubViewportContainer to transparent, otherwise it will halve the resolution of the entire screen.

UPDATE: Removed the conditional branching from the shader code, which improved performance a little bit.

## GDSCRIPT
extends ColorRect

@export var interlace_viewport : SubViewport
@onready var interlacing_material : ShaderMaterial = self.material
@export var interlacing_timer : Timer

####### Connect the interlacing timer's timeout signal here #########
func _on_interlacer_timer_timeout() -> void:
	var viewport_img : ImageTexture = ImageTexture.create_from_image(
		interlace_viewport.get_texture().get_image()
	)

	interlacing_material.set_shader_parameter("delayed_screen", viewport_img)
	interlacing_timer.start()

Shader code

// SHADER CODE
shader_type canvas_item;
uniform float line_thickness : hint_range(1.0, 100.0) = 10.0;
uniform sampler2D delayed_screen : source_color;

void fragment() {
    float screen_y = FRAGCOORD.y;
    int line_number = int(screen_y / line_thickness);
    
    float alpha = mod(float(line_number), 2.0);
    COLOR = texture(delayed_screen, SCREEN_UV);
    COLOR.a *= 1.0 - alpha;
}

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