WIP

src/utils/graphics/cached-buffer-write.test.ts

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+import { describe, expect, it, vi } from 'vitest';
+
+import {
+  createCachedFloat32BufferWrite,
+  writeFloat32BufferIfChanged,
+} from './cached-buffer-write';
+
+const createGpuWriteStub = () => {
+  const writeBuffer = vi.fn();
+  const device = {
+    queue: {
+      writeBuffer,
+    },
+  } as unknown as GPUDevice;
+
+  return { device, writeBuffer };
+};
+
+describe('cached float32 buffer writes', () => {
+  it('writes the first value set and skips unchanged values', () => {
+    const { device, writeBuffer } = createGpuWriteStub();
+    const buffer = {} as GPUBuffer;
+    const cache = createCachedFloat32BufferWrite(3);
+    const values = new Float32Array([1, 2, 3]);
+
+    expect(writeFloat32BufferIfChanged(device, buffer, values, cache)).toBe(true);
+    expect(writeBuffer).toHaveBeenCalledTimes(1);
+    expect(writeBuffer).toHaveBeenLastCalledWith(buffer, 0, values);
+
+    expect(writeFloat32BufferIfChanged(device, buffer, values, cache)).toBe(false);
+    expect(writeBuffer).toHaveBeenCalledTimes(1);
+  });
+
+  it('writes again when any float changes', () => {
+    const { device, writeBuffer } = createGpuWriteStub();
+    const buffer = {} as GPUBuffer;
+    const cache = createCachedFloat32BufferWrite(3);
+
+    expect(
+      writeFloat32BufferIfChanged(device, buffer, new Float32Array([1, 2, 3]), cache)
+    ).toBe(true);
+    expect(
+      writeFloat32BufferIfChanged(device, buffer, new Float32Array([1, 2, 4]), cache)
+    ).toBe(true);
+    expect(writeBuffer).toHaveBeenCalledTimes(2);
+  });
+
+  it('rejects cache length mismatches before writing', () => {
+    const { device, writeBuffer } = createGpuWriteStub();
+    const buffer = {} as GPUBuffer;
+    const cache = createCachedFloat32BufferWrite(2);
+
+    expect(() =>
+      writeFloat32BufferIfChanged(device, buffer, new Float32Array([1]), cache)
+    ).toThrow('Cached buffer write length mismatch');
+    expect(writeBuffer).not.toHaveBeenCalled();
+  });
+});

src/utils/graphics/cached-buffer-write.ts

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+export interface CachedFloat32BufferWrite {
+  hasValue: boolean;
+  previous: Float32Array;
+}
+
+export const createCachedFloat32BufferWrite = (
+  length: number
+): CachedFloat32BufferWrite => ({
+  hasValue: false,
+  previous: new Float32Array(length),
+});
+
+export const writeFloat32BufferIfChanged = (
+  device: GPUDevice,
+  buffer: GPUBuffer,
+  values: Float32Array,
+  cache: CachedFloat32BufferWrite
+): boolean => {
+  if (values.length !== cache.previous.length) {
+    throw new Error('Cached buffer write length mismatch');
+  }
+
+  let hasChanged = !cache.hasValue;
+  for (let i = 0; i < values.length && !hasChanged; i++) {
+    hasChanged = !Object.is(values[i], cache.previous[i]);
+  }
+
+  if (!hasChanged) {
+    return false;
+  }
+
+  cache.previous.set(values);
+  cache.hasValue = true;
+  device.queue.writeBuffer(buffer, 0, values);
+  return true;
+};