diff options
Diffstat (limited to 'public/blog/blacklight_shader/index.html')
| -rw-r--r-- | public/blog/blacklight_shader/index.html | 227 |
1 files changed, 227 insertions, 0 deletions
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 @@ +<!DOCTYPE html> +<html lang="en"> + +<head> + <meta charset="UTF-8"> + <meta name="viewport" content="width=device-width, initial-scale=1.0"> + <title>Creating a Blacklight Shader - soaos</title> +</head> + +<body> + <a href="/">Go Home</a> + <a href="..">Go Back</a> + <h1>Creating a Blacklight Shader</h1> + <font color="red"> + <b>NOTE: THIS POST WAS TRANSFERRED FROM MARKDOWN BY HAND SO I MIGHT HAVE MISSED SOME STUFF SORRY</b> + </font> + <p>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™)</p> + <p>i wanted to create a "blacklight" effect, where specific lights could reveal part of the base texture. this + shader works with <b>spot lights</b> only, but could be extended to work with point lights</p> + <figure> + <img src="blacklight.png" alt="Example of shader running, showing hidden writing on a wall" width="100%"> + <figcaption>Example of shader running, showing hidden writing on a wall.</figcaption> + </figure> + + <p>i wrote this shader in wgsl for a <a href="https://bevyengine.org" target="_blank">bevy engine</a> project, but + it should translate easily to other shading languages</p> + + <p>the finished shader can be found as part of <a href="https://git.soaos.dev/soaos/bevy_blacklight_material" + target="_blank">this repo</a></p> + + <h2>shader inputs</h2> + + <p> + for this shader, i wanted the following features: + <ul> + <li> + the number of lights should be dynamic + </li> + <li> + the revealed portion of the object should match the area illuminated by each light + </li> + <li> + the falloff of the light over distance should match the fading of the object + </li> + </ul> + + for this to work i need the following information about each light: + <ul> + <li> + position (world space) + </li> + <li> + direction (world space) + </li> + <li> + range + </li> + <li> + inner and outer angle + </li> + <li> + these will control the falloff of the light at its edges + </li> + <li> + outer angle should be less than pi/2 radians + </li> + <li> + inner angle should be less than the outer angle + </li> + </ul> + + i also need some info from the vertex shader: + <ul> + <li> + position (<b>world space!</b>) + </li> + <li> + uv + </li> + </ul> + </p> + <p>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</p> + + <p>lastly i'll take a base color texture and a sampler</p> + + <p> + with all of that, i can start off the shader by setting up the inputs and fragment entry point: + + <pre> + #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> { + } + </pre> + (bevy uses group 2 for custom shader bindings) + </p> + + <p> + since the number of lights is dynamic, i use a <a + href="https://google.github.io/tour-of-wgsl/types/arrays/runtime-sized-arrays/">storage buffer</a> to store + that information + </p> + + <h2>shader calculations</h2> + + <p>the first thing we'll need to know is how close to looking at the fragment the light source + is</p> + + <p> + we can get this information using some interesting math: + + <pre> + 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)); + </pre> + + the first step of this is taking the dot product of light direction and the direction from + the light to the fragment + </p> + + <p>since both direction vectors are normalized, the dot product will be between -1.0 and 1.0</p> + + <p> + the dot product of two unit vectors is the cosine of the angle between them (<a + href="https://math.libretexts.org/Bookshelves/Calculus/Calculus_(OpenStax)/12%3A_Vectors_in_Space/12.03%3A_The_Dot_Product#Evaluating_a_Dot_Product">proof + here</a>) + </p> + + <p> + therefore, we take the arccosine of that dot product to get the angle between the light and + the fragment + </p> + + <p> + once we have this angle we can plug it in to a falloff based on the angle properties of the + light: + + <pre> + 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); + </pre> + <pre> + fn linear_falloff_radius(factor: f32, radius: f32) -> f32 { + if factor < radius { return 1.0; } else { + return 1.0 - (factor - radius) / (1.0 - radius); + } + } + </pre> + </p> + <p> + 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: + <pre> + 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); + </pre> + <pre> + 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)); + } + } + </pre> + </p> + <p> + 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: + <pre> + let base_color = textureSample(base_texture, base_sampler, in.uv); + let final_color=base_color * angle_factor * distance_factor; + </pre> + this works for one light, but we need to refactor it to loop over all the provided blacklights: + <pre> + + @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; + } + </pre> + and with that, the shader is pretty much complete you can view the full completed shader code <a + href="https://github.com/soaosdev/bevy_blacklight_material/blob/master/assets/shaders/blacklight_material.wgsl">here</a> + </p> + <p>have fun!</p> +</body> + +</html>
\ No newline at end of file |