From ecec6d23de95423b675bc2960ccd4c3950bb4f5f Mon Sep 17 00:00:00 2001 From: Silas Bartha Date: Sat, 3 May 2025 02:16:02 -0400 Subject: Ported blog post --- public/blog/blacklight_shader/blacklight.png | Bin 0 -> 846587 bytes public/blog/blacklight_shader/index.html | 227 +++++++++++++++++++++++++++ 2 files changed, 227 insertions(+) create mode 100644 public/blog/blacklight_shader/blacklight.png create mode 100644 public/blog/blacklight_shader/index.html (limited to 'public/blog/blacklight_shader') diff --git a/public/blog/blacklight_shader/blacklight.png b/public/blog/blacklight_shader/blacklight.png new file mode 100644 index 0000000..2c5caf1 Binary files /dev/null and b/public/blog/blacklight_shader/blacklight.png differ diff --git a/public/blog/blacklight_shader/index.html b/public/blog/blacklight_shader/index.html new file mode 100644 index 0000000..db4b54e --- /dev/null +++ b/public/blog/blacklight_shader/index.html @@ -0,0 +1,227 @@ + + + + + + + Creating a Blacklight Shader - soaos + + + + Go Home + Go Back +

Creating a Blacklight Shader

+ + NOTE: THIS POST WAS TRANSFERRED FROM MARKDOWN BY HAND SO I MIGHT HAVE MISSED SOME STUFF SORRY + +

today i wanted to take a bit of time to write about a shader i implemented for my in-progress game project (more + on that soon™)

i wanted to create a "blacklight" effect, where specific lights could reveal part of the base texture. this + shader works with spot lights only, but could be extended to work with point lights

Example of shader running, showing hidden writing on a wall.

+ +

i wrote this shader in wgsl for a bevy engine project, but + it should translate easily to other shading languages

+ +

the finished shader can be found as part of this repo

+ +

shader inputs

+ +

+ for this shader, i wanted the following features: +

+ the number of lights should be dynamic +
+ the revealed portion of the object should match the area illuminated by each light +
+ the falloff of the light over distance should match the fading of the object +

+ + for this to work i need the following information about each light: +

+ position (world space) +
+ direction (world space) +
+ range +
+ inner and outer angle +
+ these will control the falloff of the light at its edges +
+ outer angle should be less than pi/2 radians +
+ inner angle should be less than the outer angle +

+ + i also need some info from the vertex shader: +

+ position (world space!) +
+ uv +

bevy's default pbr vertex shader provides this information, but as long as you can get this info into your + fragment + shader you should be good to go

+ +

lastly i'll take a base color texture and a sampler

+ +

+ with all of that, i can start off the shader by setting up the inputs and fragment entry point: + +

+	#import bevy_pbr::forward_io::VertexOutput;
+
+	struct BlackLight {
+		position: vec3<f32>,
+		direction: vec3<f32>,
+		range: f32,
+		inner_angle: f32,
+		outer_angle: f32,
+	}
+
+	@group(2) @binding(0) var<storage> lights: array<BlackLight>;
+	@group(2) @binding(1) var base_texture: texture_2d<f32>;
+	@group(2) @binding(2) var base_sampler: sampler;
+
+	@fragment
+	fn fragment(
+		in: VertexOutput,
+	) -> @location(0) vec4<f32> {
+	}
+

+ (bevy uses group 2 for custom shader bindings) +

+ +

+ since the number of lights is dynamic, i use a storage buffer to store + that information +

+ +

shader calculations

+ +

the first thing we'll need to know is how close to looking at the fragment the light source + is

+ +

+ we can get this information using some interesting math: + +

+	let light = lights[0];
+	let light_to_fragment_direction = normalize(in.world_position.xyz - light.position);
+	let light_to_fragment_angle = acos(dot(light.direction, light_to_fragment_direction));
+

+ + the first step of this is taking the dot product of light direction and the direction from + the light to the fragment +

+ +

since both direction vectors are normalized, the dot product will be between -1.0 and 1.0

+ +

+ the dot product of two unit vectors is the cosine of the angle between them (proof + here) +

+ +

+ therefore, we take the arccosine of that dot product to get the angle between the light and + the fragment +

+ +

+ once we have this angle we can plug it in to a falloff based on the angle properties of the + light: + +

+	let angle_inner_factor = light.inner_angle/light.outer_angle;
+	let angle_factor = linear_falloff_radius(light_to_fragment_angle / light.outer_angle, angle_inner_factor);
+

+	fn linear_falloff_radius(factor: f32, radius: f32) -> f32 {
+		if factor < radius { return 1.0; } else { 
+			return 1.0 - (factor - radius) / (1.0 - radius); 
+		} 
+	}
+

+ next, we need to make sure the effect falls off properly over distance we can do this by getting the distance + from the light to + the fragment and normalizing it with the range of the light before plugging that into an inverse square falloff + we'll use squared distance to avoid expensive and unnecessary square root operations: +

+	let light_distance_squared=distance_squared(in.world_position.xyz, light.position);
+	let distance_factor=inverse_falloff_radius(saturate(light_distance_squared / (light.range * light.range)), 0.5);
+

+	fn distance_squared(a: vec3f, b: vec3f) -> f32 {
+		let vec = a - b;
+		return dot(vec, vec);
+	}
+
+	fn inverse_falloff(factor: f32) -> f32 {
+		return pow(1.0 - factor, 2.0);
+	}
+
+	fn inverse_falloff_radius(factor: f32, radius: f32) -> f32 {
+		if factor < radius { return 1.0; } else { 
+			return inverse_falloff((factor - radius) / (1.0 - radius)); 
+		}
+	}
+

+ now we'll have a float multiplier between 0.0 and 1.0 for our angle and distance to the light we can get the + resulting color by multiplying these with the base color texture: +

+	let base_color = textureSample(base_texture, base_sampler, in.uv);
+	let final_color=base_color * angle_factor * distance_factor;
+

+ this works for one light, but we need to refactor it to loop over all the provided blacklights: +

+
+	@fragment fn fragment( in: VertexOutput ) -> @location(0) vec4<f32> {
+		let base_color = textureSample(base_texture, base_sampler, in.uv);
+		var final_color = vec4f(0.0, 0.0, 0.0, 0.0);
+		for (var i = u32(0); i < arrayLength(&lights); i = i+1) { 
+			let light=lights[i];
+			let light_to_fragment_direction = normalize(in.world_position.xyz - light.position);
+			let light_to_fragment_angle = acos(dot(light.direction, light_to_fragment_direction));
+			let angle_inner_factor = light.inner_angle / light.outer_angle;
+			let angle_factor = linear_falloff_radius(light_to_fragment_angle / light.outer_angle, angle_inner_factor);
+			let light_distance_squared = distance_squared(in.world_position.xyz, light.position);
+			let distance_factor = inverse_falloff_radius(saturate(light_distance_squared / (light.range * light.range)), 0.5);
+			final_color = saturate(final_color + base_color * angle_factor * distance_factor);
+		} 
+		return final_color; 
+	}
+

+ and with that, the shader is pretty much complete you can view the full completed shader code here +

have fun!

+ + + \ No newline at end of file -- cgit v1.2.3