Color cycling hit effect

Inspired by Shovel Knight I made a shader for the color cycling damage effect on enemies. Note that it is not an exact copy. Cycles through the colors and offsets the starting frame based on the pixel’s brightness.

Use it by animating the current_frame parameter. You can adjust start_frame to offset the sequence, for example to start with the red color on both a dark and light sprite. You can optionally mix the colors with the sprite if you want a more subtle effect. Don’t use negative numbers in the parameters.

Personally I run it at 30 FPS with 7 frames (0 -> 6), then disable the shader on frame 8.

Sprite art in cover image by Redshrike, licensed CC-BY 3.0. https://opengameart.org/content/tower-defense-prototyping-assets-4-monsters-some-tiles-a-background-image

Shader code
shader_type canvas_item;

uniform int start_frame = 0;
uniform int current_frame = 0;
uniform float mix_ratio = 1.0;

const vec3 colors[6] = vec3[] (
	vec3(1.0, 0.0, 0.0), // Red
	vec3(0.5, 0.0, 0.0), // Dark red
	vec3(0.0, 0.0, 0.0), // Black
	vec3(0.0, 0.0, 1.0), // Blue
	vec3(0.0, 0.0, 0.5), // Dark blue
	vec3(0.0, 0.0, 0.0)  // Black
);

void fragment() {
	// https://en.wikipedia.org/wiki/Rec._709#Luma_coefficients
	float brightness = dot(COLOR.rgb, vec3(0.2126, 0.7152, 0.0722));

	// Calculate the starting frame based on brightness
	int offset = 0;
	if (brightness > 0.75) {
		offset = 2;
	} else if (brightness > 0.25) {
		offset = 1;
	}

	// Get the color, wrapping around at the end of the array
	int color_index = (start_frame + current_frame + offset) % colors.length();
	vec3 color = colors[color_index];

	// Apply the color to the sprite
	COLOR = vec4(mix(COLOR.rgb, color, mix_ratio), COLOR.a);
}
Tags
flash, impact
The shader code and all code snippets in this post are under CC0 license and can be used freely without the author's permission. Images and videos, and assets depicted in those, do not fall under this license. For more info, see our License terms.

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