Galactica/crates/render/shaders/starfield.wgsl

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// INCLUDE: global uniform header
struct InstanceInput {
@location(2) position: vec3<f32>,
@location(3) size: f32,
@location(4) tint: vec2<f32>,
};
struct VertexInput {
@location(0) position: vec3<f32>,
@location(1) texture_coords: vec2<f32>,
}
struct VertexOutput {
@builtin(position) position: vec4<f32>,
@location(0) texture_coords: vec2<f32>,
@location(1) texture_index: u32,
@location(2) tint: vec2<f32>,
}
@group(0) @binding(0)
var texture_array: binding_array<texture_2d<f32>>;
@group(0) @binding(1)
var sampler_array: binding_array<sampler>;
fn fmod(x: vec2<f32>, m: f32) -> vec2<f32> {
return x - floor(x / m) * m;
}
@vertex
fn vertex_main(
vertex: VertexInput,
instance: InstanceInput,
) -> VertexOutput {
var out: VertexOutput;
out.tint = instance.tint;
// Center of the tile the camera is currently in, in game coordinates.
// x div y = x - (x mod y)
let tile_center = (
global_data.camera_position.xy
- (
fmod(
global_data.camera_position.xy + global_data.starfield_tile_size.x / 2.0,
global_data.starfield_tile_size.x
) - global_data.starfield_tile_size.x / 2.0
)
);
let zoom_min_times = (
global_data.camera_zoom.x / global_data.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_data.starfield_size_limits.y - global_data.starfield_size_limits.x)
+ (global_data.starfield_size_limits.x)
)
) {
out.position = vec4<f32>(2.0, 2.0, 0.0, 1.0);
return out;
}
// Apply sprite aspect ratio & scale factor
// also applies screen aspect ratio
// Note that we do NOT scale for distance here---this is intentional.
var scale: f32 = instance.size / global_data.camera_zoom.x;
// Minimum scale to prevent flicker at large zoom levels
var real_size = scale * global_data.window_size.xy;
if (real_size.x < 2.0 || real_size.y < 2.0) {
// Otherwise, clamp to a minimum scale
scale = 2.0 / max(global_data.window_size.x, global_data.window_size.y);
}
// Divide by two, because viewport height is 2 in screen units
// (coordinates go from -1 to 1)
var pos: vec2<f32> = vec2<f32>(
vertex.position.x * (scale/2.0) / global_data.window_aspect.x,
vertex.position.y * (scale/2.0)
);
// 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_data.camera_position.xy;
// Translate
pos = pos + (
// Don't forget to correct distance for screen aspect ratio too!
(camera_pos / (global_data.camera_zoom.x * instance.position.z))
/ vec2<f32>(global_data.window_aspect.x, 1.0)
);
out.position = vec4<f32>(pos, 0.0, 1.0) * instance.position.z;
// Starfield sprites may not be animated
let t = global_atlas[global_data.starfield_sprite.x];
out.texture_index = u32(t.atlas_texture);
out.texture_coords = vec2(t.xpos, t.ypos);
if vertex.texture_coords.x == 1.0 {
out.texture_coords = vec2(out.texture_coords.x + t.width, out.texture_coords.y);
}
if vertex.texture_coords.y == 1.0 {
out.texture_coords = vec2(out.texture_coords.x, out.texture_coords.y + t.height);
}
return out;
}
@fragment
fn fragment_main(in: VertexOutput) -> @location(0) vec4<f32> {
let b = 0.8 - (in.tint.x / 1.5); // brightness
let c = in.tint.y; // color
// TODO: saturation
// TODO: more subtle starfield
// TODO: blur stars more?
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;
return textureSampleLevel(
texture_array[in.texture_index],
sampler_array[0],
in.texture_coords,
0.0
).rgba * vec4<f32>(
(c_top + (c_del * c)) * b,
1.0
);
}