fp64 checker plane

// ═══ typeshade example — fp64 world-plane checkerboard ═══
//
// The map-engine failure mode in its purest form: a 1×1-unit checkerboard on
// a world plane, viewed 100 million units from the origin (ulp_f32(1e8) = 8 —
// EIGHT whole cells wide). The tile grid is recovered with floor/fract ON THE
// f64 TYPE (both are in the df64 whitelist): parity = fract((⌊x⌋+⌊y⌋)/2)
// stays exact because ⌊x⌋ at 1e8 does not FIT in an f32 — narrowing first is
// precisely the bug. The plain-f32 left half only ever sees the coordinate in
// 8-cell steps — parity never flips and the checker collapses FLAT; the f64
// right half stays a crisp checkerboard with anti-aliased cell borders.
//
// The `_fp64` guard uniform is auto-injected by the lowering; the render
// harnesses bind it to 1.0f by probing the program for the Fp64Guard block.

import {
  fn,
  module,
  vec3,
  vec4,
  f32,
  pow,
  floor,
  fract,
  min,
  mix,
  step,
  smoothstep,
  toF32,
  toF64,
  f32T,
  vec2fT,
  vec2f64T,
  Let,
  uniformStruct,
} from '../src/index.js';
import { VsOut, vs } from './_fullscreen.js';
import type { ShaderExample } from './_shared.js';

const U = uniformStruct(
  'Uniforms',
  { group: 0, binding: 0, as: 'u' },
  {
    center: vec2f64T, // one DF64Vec2 slot — host packs [hi.x, hi.y, lo.x, lo.y]
    resolution: vec2fT,
    zoom_exp: f32T, // view span = 10^-zoom_exp world units (negative = zoom out)
    fp64: f32T, // toggle: 1 = split-screen f32 | f64 (canonical), 0 = all-f32
  },
);

const fsChecker = fn(
  'fs_checker',
  { vo: VsOut },
  (p) => {
    const span = Let(pow(f32(10.0), U.field.zoom_exp.neg()));
    const half = Let(p.vo.uv.x.mul(2.0));
    const sx = Let(half.sub(p.vo.uv.x.lt(0.5).select(0.0, 1.0)));
    const dx = Let(sx.sub(0.5).mul(span));
    const dy = Let(
      p.vo.uv.y.sub(0.5).mul(span).mul(U.field.resolution.y.div(U.field.resolution.x).mul(2.0)),
    );

    const isF32 = Let(p.vo.uv.x.lt(0.5).or(U.field.fp64.lt(0.5)));
    // f64 path — floor/fract in extended precision; only RESULTS narrow
    // (cell parity is 0/0.5 exactly; the in-cell fraction is sub-unit).
    const px = Let(U.field.center.x.add(toF64(dx)));
    const py = Let(U.field.center.y.add(toF64(dy)));
    const par64 = Let(toF32(fract(floor(px).add(floor(py)).mul(0.5))));
    const fx64 = Let(toF32(fract(px)));
    const fy64 = Let(toF32(fract(py)));
    // f32 twin — SAME formulas, world coordinate narrowed first: at 1e8 the
    // coordinate moves in 8-cell steps, so parity NEVER flips (always even)
    // and the fraction is identically 0 — the half renders flat.
    const px32 = Let(toF32(U.field.center.x).add(dx));
    const py32 = Let(toF32(U.field.center.y).add(dy));
    const par32 = Let(fract(floor(px32).add(floor(py32)).mul(0.5)));
    const fx32 = Let(fract(px32));
    const fy32 = Let(fract(py32));

    const par = Let(isF32.select(par32, par64));
    const fx = Let(isF32.select(fx32, fx64));
    const fy = Let(isF32.select(fy32, fy64));

    // Two-tone slate/ivory checker + anti-aliased cell borders. The AA width
    // comes from the analytic pixel size in WORLD units (span / half-width in
    // px) — fwidth(fract(x)) would spike across the cell seam itself.
    const chk = Let(step(0.25, par));
    const edge = Let(min(min(fx, f32(1).sub(fx)), min(fy, f32(1).sub(fy))));
    const pixw = Let(span.div(U.field.resolution.x.mul(0.5)));
    const line = Let(smoothstep(f32(0), pixw.mul(1.5).add(1e-9), edge));
    const ivory = vec3(0.93, 0.9, 0.82);
    const slate = vec3(0.23, 0.29, 0.36);
    const rgb = mix(ivory, slate, chk).mul(mix(f32(0.35), f32(1.0), line));
    return vec4(rgb, f32(1));
  },
  { stage: 'fragment', retAttr: '@location(0)' },
);

// `_fp64` guard lands at (group 0, binding 1) automatically.
const fp64CheckerPlaneModule = module({
  funcs: [vs, fsChecker],
  uses: [U, VsOut],
});

export const fp64CheckerPlane: ShaderExample = {
  id: 'fp64-checker-plane',
  title: 'fp64 checker plane',
  blurb:
    'A 1-unit checkerboard on a world plane. Drag the DISTANCE slider (or wheel) to carry the plane out from the origin: near 10⁶ both halves are a crisp checker, but past ~10⁷·² one f32 ulp grows wider than a cell and the plain-f32 left half collapses flat (parity can no longer flip) — while the f64 right half, doing floor/fract on the emulated-double type, keeps cell parity and anti-aliased borders all the way to 10⁹. Watch the exact distance where f32 gives out; flip the fp64 toggle to collapse the right half too.',
  category: 'cartographic',
  file: 'fp64-checker-plane.ts',
  module: fp64CheckerPlaneModule,
  renderable: true,
  splitLabels: ['f32', 'f64 (emulated)'],
  controls: {
    // Sweep the plane's distance from the origin: base·10^mag + offset (the
    // fractional offset is the sub-cell detail f32 loses first). At mag = 8 this
    // is the classic 10⁸ view; drop to 6 and f32 is fine — the point is the
    // THRESHOLD in between, which the viewer drives.
    center: { kind: 'logmag2d', magField: 'mag', base: [1, 0.5], offset: [0.3, 0.7] },
    resolution: { kind: 'resolution' },
    mag: {
      kind: 'slider',
      label: 'Distance from origin 10^x',
      min: 4,
      max: 9,
      step: 0.02,
      value: 6,
      wheel: true,
    },
    // View span across each half (10^-zoom_exp world units ≈ number of cells).
    zoom_exp: {
      kind: 'slider',
      label: 'Zoom 10^-x',
      min: -2,
      max: 5,
      step: 0.05,
      value: -0.9,
    },
    fp64: { kind: 'toggle', label: 'fp64 emulation', value: true },
  },
};

struct Uniforms {
  @align(16) center: DF64Vec2,
  resolution: vec2<f32>,
  zoom_exp: f32,
  fp64: f32,
}

struct VsOut {
  @builtin(position) pos: vec4<f32>,
  @location(0) uv: vec2<f32>,
}

struct DF64Vec2 {
  hi: vec2<f32>,
  lo: vec2<f32>,
}

@group(0) @binding(0) var<uniform> u: Uniforms;
@group(0) @binding(1) var _fp64: texture_2d<f32>;

@vertex
fn vs(@builtin(vertex_index) vi: u32) -> VsOut {
  let _cse0 = ((f32((vi & 1u)) * 4.0) - 1.0);
  let _cse1 = ((f32((vi >> 1u)) * 4.0) - 1.0);
  return VsOut(vec4<f32>(_cse0, _cse1, 0.0, 1.0), vec2<f32>(((_cse0 * 0.5) + 0.5), ((_cse1 * 0.5) + 0.5)));
}

@fragment
fn fs_checker(vo: VsOut) -> @location(0) vec4<f32> {
  let _fp64_g = textureLoad(_fp64, vec2<i32>(0, 0), 0).x;
  let _v0 = pow(10.0, (-u.zoom_exp));
  let _v1 = (vo.uv.x * 2.0);
  let _cse0 = (vo.uv.x < 0.5);
  let _v2 = (_v1 - select(1.0, 0.0, _cse0));
  let _v3 = ((_v2 - 0.5) * _v0);
  let _v4 = (((vo.uv.y - 0.5) * _v0) * ((u.resolution.y / u.resolution.x) * 2.0));
  let _v5 = (_cse0 || (u.fp64 < 0.5));
  let _cse1 = vec2<f32>(u.center.hi.x, u.center.lo.x);
  let _v6 = df64_add(_cse1, vec2<f32>(_v3, 0.0), _fp64_g);
  let _cse2 = vec2<f32>(u.center.hi.y, u.center.lo.y);
  let _v7 = df64_add(_cse2, vec2<f32>(_v4, 0.0), _fp64_g);
  let _v8 = df64_narrow(df64_fract((df64_add(df64_floor(_v6, _fp64_g), df64_floor(_v7, _fp64_g), _fp64_g) * 0.5), _fp64_g));
  let _cse4 = bitcast<f32>(bitcast<u32>(0.0));
  let _cse3 = vec2<f32>(_cse4, _cse4);
  let _v9 = df64_narrow(df64_fract(df64_add(_v6, _cse3, _fp64_g), _fp64_g));
  let _v10 = df64_narrow(df64_fract(df64_add(_v7, _cse3, _fp64_g), _fp64_g));
  let _v11 = (df64_narrow(_cse1) + _v3);
  let _v12 = (df64_narrow(_cse2) + _v4);
  let _v13 = fract(((floor(_v11) + floor(_v12)) * 0.5));
  let _v14 = fract(_v11);
  let _v15 = fract(_v12);
  let _v16 = select(_v8, _v13, _v5);
  let _v17 = select(_v9, _v14, _v5);
  let _v18 = select(_v10, _v15, _v5);
  let _v19 = step(0.25, _v16);
  let _v20 = min(min(_v17, (1.0 - _v17)), min(_v18, (1.0 - _v18)));
  let _v21 = (_v0 / (u.resolution.x * 0.5));
  let _v22 = smoothstep(0.0, ((_v21 * 1.5) + 1e-9), _v20);
  return vec4<f32>((mix(vec3<f32>(0.93, 0.9, 0.82), vec3<f32>(0.23, 0.29, 0.36), _v19) * mix(0.35, 1.0, _v22)), 1.0);
}

fn df64_twoSum(a: f32, b: f32, _fp64_g: f32) -> vec2<f32> {
  let _v0 = (a + b);
  let _v1 = (((_v0 * _fp64_g) - a) * _fp64_g);
  let _v2 = (((a - ((_v0 - _v1) * _fp64_g)) * _fp64_g) + (b - _v1));
  return vec2<f32>(_v0, _v2);
}

fn df64_quickTwoSum(a: f32, b: f32, _fp64_g: f32) -> vec2<f32> {
  let _v0 = ((a + b) * _fp64_g);
  let _v1 = (b - ((_v0 - a) * _fp64_g));
  return vec2<f32>(_v0, _v1);
}

fn df64_add(a: vec2<f32>, b: vec2<f32>, _fp64_g: f32) -> vec2<f32> {
  var _v0: vec2<f32> = df64_twoSum(a.x, b.x, _fp64_g);
  let _v1 = df64_twoSum(a.y, b.y, _fp64_g);
  _v0.y = (_v0.y + _v1.x);
  _v0 = df64_quickTwoSum(_v0.x, _v0.y, _fp64_g);
  _v0.y = (_v0.y + _v1.y);
  _v0 = df64_quickTwoSum(_v0.x, _v0.y, _fp64_g);
  return _v0;
}

fn df64_sub(a: vec2<f32>, b: vec2<f32>, _fp64_g: f32) -> vec2<f32> {
  return df64_add(a, (-b), _fp64_g);
}

fn df64_floor(a: vec2<f32>, _fp64_g: f32) -> vec2<f32> {
  let _v0 = floor(a.x);
  return select(vec2<f32>(_v0, 0.0), df64_quickTwoSum(_v0, floor(a.y), _fp64_g), (_v0 == a.x));
}

fn df64_fract(a: vec2<f32>, _fp64_g: f32) -> vec2<f32> {
  return df64_sub(a, df64_floor(a, _fp64_g), _fp64_g);
}

fn df64_narrow(a: vec2<f32>) -> f32 {
  return (a.x + a.y);
}

#version 300 es
precision highp float;
precision highp int;

out vec2 uv;

void main() {
  uint vi = uint(gl_VertexID);
  float _cse0 = ((float((vi & 1u)) * 4.0) - 1.0);
  float _cse1 = ((float((vi >> 1u)) * 4.0) - 1.0);
  gl_Position = vec4(_cse0, _cse1, 0.0, 1.0);
  uv = vec2(((_cse0 * 0.5) + 0.5), ((_cse1 * 0.5) + 0.5));
}

#version 300 es
precision highp float;
precision highp int;

struct DF64Vec2 {
  vec2 hi;
  vec2 lo;
};
layout(std140) uniform Uniforms {
  DF64Vec2 center;
  vec2 resolution;
  float zoom_exp;
  float fp64;
} u;

uniform highp sampler2D _fp64;
vec2 df64_twoSum(float a, float b, float _fp64_g) {
  float _v0 = (a + b);
  float _v1 = (((_v0 * _fp64_g) - a) * _fp64_g);
  float _v2 = (((a - ((_v0 - _v1) * _fp64_g)) * _fp64_g) + (b - _v1));
  return vec2(_v0, _v2);
}

vec2 df64_quickTwoSum(float a, float b, float _fp64_g) {
  float _v0 = ((a + b) * _fp64_g);
  float _v1 = (b - ((_v0 - a) * _fp64_g));
  return vec2(_v0, _v1);
}

vec2 df64_add(vec2 a, vec2 b, float _fp64_g) {
  vec2 _v0 = df64_twoSum(a.x, b.x, _fp64_g);
  vec2 _v1 = df64_twoSum(a.y, b.y, _fp64_g);
  _v0.y = (_v0.y + _v1.x);
  _v0 = df64_quickTwoSum(_v0.x, _v0.y, _fp64_g);
  _v0.y = (_v0.y + _v1.y);
  _v0 = df64_quickTwoSum(_v0.x, _v0.y, _fp64_g);
  return _v0;
}

vec2 df64_sub(vec2 a, vec2 b, float _fp64_g) {
  return df64_add(a, (-b), _fp64_g);
}

vec2 df64_floor(vec2 a, float _fp64_g) {
  float _v0 = floor(a.x);
  return ((_v0 == a.x) ? df64_quickTwoSum(_v0, floor(a.y), _fp64_g) : vec2(_v0, 0.0));
}

vec2 df64_fract(vec2 a, float _fp64_g) {
  return df64_sub(a, df64_floor(a, _fp64_g), _fp64_g);
}

float df64_narrow(vec2 a) {
  return (a.x + a.y);
}
in vec2 uv;
layout(location = 0) out vec4 _ret;

void main() {
  float _fp64_g = texelFetch(_fp64, ivec2(0, 0), 0).x;
  float _v0 = pow(10.0, (-u.zoom_exp));
  float _v1 = (uv.x * 2.0);
  bool _cse0 = (uv.x < 0.5);
  float _v2 = (_v1 - (_cse0 ? 0.0 : 1.0));
  float _v3 = ((_v2 - 0.5) * _v0);
  float _v4 = (((uv.y - 0.5) * _v0) * ((u.resolution.y / u.resolution.x) * 2.0));
  bool _v5 = (_cse0 || (u.fp64 < 0.5));
  vec2 _cse1 = vec2(u.center.hi.x, u.center.lo.x);
  vec2 _v6 = df64_add(_cse1, vec2(_v3, 0.0), _fp64_g);
  vec2 _cse2 = vec2(u.center.hi.y, u.center.lo.y);
  vec2 _v7 = df64_add(_cse2, vec2(_v4, 0.0), _fp64_g);
  float _v8 = df64_narrow(df64_fract((df64_add(df64_floor(_v6, _fp64_g), df64_floor(_v7, _fp64_g), _fp64_g) * 0.5), _fp64_g));
  float _cse4 = uintBitsToFloat(floatBitsToUint(0.0));
  vec2 _cse3 = vec2(_cse4, _cse4);
  float _v9 = df64_narrow(df64_fract(df64_add(_v6, _cse3, _fp64_g), _fp64_g));
  float _v10 = df64_narrow(df64_fract(df64_add(_v7, _cse3, _fp64_g), _fp64_g));
  float _v11 = (df64_narrow(_cse1) + _v3);
  float _v12 = (df64_narrow(_cse2) + _v4);
  float _v13 = fract(((floor(_v11) + floor(_v12)) * 0.5));
  float _v14 = fract(_v11);
  float _v15 = fract(_v12);
  float _v16 = (_v5 ? _v13 : _v8);
  float _v17 = (_v5 ? _v14 : _v9);
  float _v18 = (_v5 ? _v15 : _v10);
  float _v19 = step(0.25, _v16);
  float _v20 = min(min(_v17, (1.0 - _v17)), min(_v18, (1.0 - _v18)));
  float _v21 = (_v0 / (u.resolution.x * 0.5));
  float _v22 = smoothstep(0.0, ((_v21 * 1.5) + 1e-9), _v20);
  _ret = vec4((mix(vec3(0.93, 0.9, 0.82), vec3(0.23, 0.29, 0.36), _v19) * mix(0.35, 1.0, _v22)), 1.0);
}