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diff --git a/public/blog/blacklight_shader/index.html b/public/blog/blacklight_shader/index.html deleted file mode 100644 index db4b54e..0000000 --- a/public/blog/blacklight_shader/index.html +++ /dev/null @@ -1,227 +0,0 @@ -<!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>
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