[DRAFT] A proxy function parameter

[iwoplaza]

Proxy parameters are comptime params to a non-comptime function, with the possibility to give access to runtime values.

A mutable context object that doesn't require access through .$

interface Ctx {
  result: number;
}

const callback = (ctx: Ctx) => {
  'use gpu';
  ctx.result = 123;
};

const CtxStruct = d.struct({
  result: d.f32,
});

const ctxProxy = tgpu.proxy<Ctx>({
  // This will be the type that will be replace the proxy.
  // Can be left empty, in which case the parameter will
  // not be reflected in the final WGSL code.
  substitute: d.ptrFn(CtxStruct),
  value: {
    // Access to any prop can be redirected
    // In this case, access to any prop on this proxy
    // is redirected to being an access on the 'substitute'.
    result: (sub) => sub.$.result,
  },
});

const shelled = tgpu.fn([ctxProxy, d.f32])(callback);

Generated WGSL:

fn item(ctx: ptr<function, CtxStruct>) {
  (*ctx).result = 123f;
}

Access to a private variable

interface RandCtx {
  seed2: d.v2f;
}

export function rand01(ctx: RandCtx) {
  'use gpu';
  const a = dot(ctx.seed2, d.vec2f(23.14077926, 232.61690225));
  const b = dot(ctx.seed2, d.vec2f(54.47856553, 345.84153136));
  ctx.seed2.x = fract(cos(a) * 136.8168);
  ctx.seed2.y = fract(cos(b) * 534.7645);
  return ctx.seed2.y;
}

export function createRandCtx() {
  const seedVar = tgpu.privateVar(d.vec2f);
  
  return tgpu.proxy<RandCtx>({
    value: {
      seed2: () => seedVar.$,
    },
  });
}

const ctx1 = createRandCtx();
const ctx2 = createRandCtx();

const main = () => {
  'use gpu';
   // separate states
  const first = rand01(ctx1.$);
  const second = rand01(ctx2.$);
};

[iwoplaza]

This might very possibly be possible using #3028