Galactica/crates/render/shaders/starfield.wgsl

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struct InstanceInput {
@location(2) position: vec3<f32>,
@location(3) size: f32,
@location(4) tint: vec2<f32>,
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};
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struct VertexInput {
@location(0) position: vec3<f32>,
@location(1) texture_coords: vec2<f32>,
}
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struct VertexOutput {
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@builtin(position) position: vec4<f32>,
@location(0) texture_coords: vec2<f32>,
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@location(1) tint: vec2<f32>,
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}
@group(1) @binding(0)
var<uniform> global: GlobalUniform;
struct GlobalUniform {
camera_position: vec2<f32>,
camera_zoom: vec2<f32>,
camera_zoom_limits: vec2<f32>,
window_size: vec2<f32>,
window_aspect: vec2<f32>,
starfield_texture: vec2<u32>,
starfield_tile_size: vec2<f32>,
starfield_size_limits: vec2<f32>,
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};
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@group(0) @binding(0)
var texture_array: binding_array<texture_2d<f32>>;
@group(0) @binding(1)
var sampler_array: binding_array<sampler>;
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fn fmod(x: vec2<f32>, m: f32) -> vec2<f32> {
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return x - floor(x / m) * m;
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}
@vertex
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fn vertex_main(
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vertex: VertexInput,
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instance: InstanceInput,
) -> VertexOutput {
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var out: VertexOutput;
out.texture_coords = vertex.texture_coords;
out.tint = instance.tint;
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// Center of the tile the camera is currently in, in game coordinates.
// x div y = x - (x mod y)
let tile_center = (
global.camera_position.xy
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- (
fmod(
global.camera_position.xy + global.starfield_tile_size.x / 2.0,
global.starfield_tile_size.x
) - global.starfield_tile_size.x / 2.0
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)
);
let zoom_min_times = (
global.camera_zoom.x / global.camera_zoom_limits.x
);
// Hide n% of the smallest stars
// If we wanted a constant number of stars on the screen, we would do
// `let hide_fraction = 1.0 - 1.0 / (zoom_min_times * zoom_min_times);`
// We, however, don't want this: a bigger screen should have more stars,
// but not *too* many. We thus scale linearly.
let hide_fraction = 1.0 - 1.0 / (zoom_min_times * 0.8);
if (
instance.size < (
hide_fraction * (global.starfield_size_limits.y - global.starfield_size_limits.x)
+ (global.starfield_size_limits.x)
)
) {
out.position = vec4<f32>(2.0, 2.0, 0.0, 1.0);
return out;
}
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// Apply sprite aspect ratio & scale factor
// also applies screen aspect ratio
// Note that we do NOT scale for distance here---this is intentional.
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var scale: f32 = instance.size / global.camera_zoom.x;
// Minimum scale to prevent flicker at large zoom levels
var real_size = scale * global.window_size.xy;
if (real_size.x < 2.0 || real_size.y < 2.0) {
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// Otherwise, clamp to a minimum scale
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scale = 2.0 / max(global.window_size.x, global.window_size.y);
}
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// Divide by two, because viewport height is 2 in screen units
// (coordinates go from -1 to 1)
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var pos: vec2<f32> = vec2<f32>(
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vertex.position.x * (scale/2.0) / global.window_aspect.x,
vertex.position.y * (scale/2.0)
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);
// World position relative to camera
// (Note that instance position is in a different
// coordinate system than usual)
let camera_pos = (instance.position.xy + tile_center) - global.camera_position.xy;
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// Translate
pos = pos + (
// Don't forget to correct distance for screen aspect ratio too!
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(camera_pos / (global.camera_zoom.x * instance.position.z))
/ vec2<f32>(global.window_aspect.x, 1.0)
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);
out.position = vec4<f32>(pos, 0.0, 1.0) * instance.position.z;
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return out;
}
@fragment
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fn fragment_main(in: VertexOutput) -> @location(0) vec4<f32> {
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let b = 0.8 - (in.tint.x / 1.5); // brightness
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let c = in.tint.y; // color
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// TODO: saturation
// TODO: more subtle starfield
// TODO: blur stars more?
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let c_top = vec3<f32>(0.369, 0.819, 0.796);
let c_bot = vec3<f32>(0.979, 0.556, 0.556);
let c_del = c_bot - c_top;
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return textureSampleLevel(
texture_array[global.starfield_texture.x],
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sampler_array[0],
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in.texture_coords,
0.0
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).rgba * vec4<f32>(
(c_top + (c_del * c)) * b,
1.0
);
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}