Evaluate generating vertex data into a mapped buffer (as opposed to generating and writing separately)

[rdw-software]

See https://toji.dev/webgpu-best-practices/buffer-uploads - from "Buffers that are written once and never change".

Lots of geometry has this property, but it's unclear whether switching from writeBuffer to this would be worth it. Benchmarks?

// Creates a grid of vertices on the X, Y plane
function createXYPlaneVertexBuffer(width, height) {
  const vertexSize = 3 * Float32Array.BYTES_PER_ELEMENT; // Each vertex is 3 floats (X,Y,Z position)

  const vertexBuffer = gpuDevice.createBuffer({
    size: width * height * vertexSize, // Allocate enough space for all the vertices
    usage: GPUBufferUsage.VERTEX, // COPY_DST is not required!
    mappedAtCreation: true,
  });

  const vertexPositions = new Float32Array(vertexBuffer.getMappedRange()),

  // Build the vertex grid
  for (let y = 0; y < height; ++y) {
    for (let x = 0; x < width; ++x) {
      const vertexIndex = y * width + x;
      const offset = vertexIndex * 3;

      vertexPositions[offset + 0] = x;
      vertexPositions[offset + 1] = y;
      vertexPositions[offset + 2] = 0;
    }
  }

  // Commit the buffer contents to the GPU
  vertexBuffer.unmap();

  return vertexBuffer;
}