UV light (2D and 3D)

This is an example of a “UV light” effect, useful for secret objects and messages. It works both with 3D geometry (where the shape is defined by a mesh) and with flat objects (where the shape/pattern is defined by texture’s alpha).

Requirements:

  • put all secret objects in a separate layer (property layers, in this example it’s “Layer 2”)
  • remove that layer from normal light sources (property light_cull_mask)
  • make sure that UV light sources affect that layer (property light_cull_mask)
Shader code
// 2D objects, e.g. text on a wall, where the shape is defined by a texture
shader_type spatial;

uniform sampler2D tex;
uniform vec4 color: source_color = vec4(0, 1, 1, 1);
uniform float energy: hint_range(0, 16) = 1;

void fragment() {
	EMISSION = color.rgb * energy;
	ALPHA = 0.0;
}

void light() {
	vec4 pixel = textureLod(tex, UV, 1.0);
	DIFFUSE_LIGHT = vec3(0.0);
	SPECULAR_LIGHT = vec3(0.0);
	ALPHA = ATTENUATION * pixel.a;
	if (ATTENUATION == 1.0) {
		ALPHA = 0.0;
	}
}

// 3D objects, e.g. a ghost, where the shape is defined by geometry
shader_type spatial;

uniform vec4 color: source_color = vec4(0, 1, 1, 1);
uniform float energy: hint_range(0, 16) = 1;

void fragment() {
	EMISSION = color.rgb * energy;
	ALPHA = 0.0;
}

void light() {
	DIFFUSE_LIGHT = vec3(0.0);
	SPECULAR_LIGHT = vec3(0.0);
	ALPHA = ATTENUATION;
	if (ATTENUATION == 1.0) {
		ALPHA = 0.0;
	}
}
Tags
hidden, light, Transparency, uv
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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ignawesome
ignawesome
7 months ago

Love this shader! It has one issue I need to solve though… If you aim a non-UV light that doesn’t reveal the message, it stays dark and doesn’t react to the light because you cannot set different cull masks for different materials in one object.