Screen Damage Flash (Square Gradient Hit Effect)

A lightweight full-screen hit flash shader for 2D games.

This shader creates a red (or any color) damage-flash overlay when the player gets hit.
The effect appears stronger at the screen edges and fades toward the center, using a smooth square-shaped gradient instead of a circular one.

Perfect for HUDs, player damage feedback, and cinematic impact flashes.

💡 Features

Center-to-edge smooth gradient (square shape).
Configurable flash color and intensity.
Adjustable center size, feather width, and edge hardness.
Works with any screen resolution (uses UV coordinates).
Fully GPU-driven — no texture sampling, minimal performance cost.

⚙️ Usage

Add a CanvasLayer with a full-screen ColorRect.
Assign this shader to the ColorRect’s material.
Trigger the flash by animating the intensity parameter (e.g. with a Tween).

Example GDScript:

🎨 Parameters

Name	Type	Description
`flash_color`	`vec4`	The color of the flash.
`intensity`	`float`	Current flash strength (animate this).
`inner_ratio`	`float`	Size of the light center area.
`feather`	`float`	Width of the soft transition area.
`edge_power`	`float`	Edge contrast (higher = harder edge).

Only tested on Godot 4.5 stable, and I am not sure about its availablity on other version of Godot.

Shader code

shader_type canvas_item;

uniform vec4  flash_color : source_color = vec4(1.0, 0.0, 0.0, 1.0);
uniform float intensity   : hint_range(0.0, 1.0) = 0.0;  
uniform float edge_power  : hint_range(0.1, 4.0) = 2.5;  
uniform float inner_ratio : hint_range(0.0, 1.0) = 0.75;  
uniform float feather     : hint_range(0.01, 1.0) = 0.4; 

void fragment() {

    vec2 uv = UV * 2.0 - 1.0;


    float dist = max(abs(uv.x), abs(uv.y));


    float a = smoothstep(inner_ratio, inner_ratio + feather, dist);
    a = pow(a, edge_power);
    a *= intensity;

    COLOR = vec4(flash_color.rgb, a * flash_color.a);
}