Function createStructArrayElementProxy

src/strands/ir_builders.js:657–752

(strandsContext, bufferNode, indexNode, schema)

}

export function createStructArrayElementProxy(strandsContext, bufferNode, indexNode, schema) {
  const { dag, cfg } = strandsContext;

  // Ensure index is a StrandsNode
  let index;
  if (indexNode instanceof StrandsNode) {
    index = indexNode;
  } else {
    const { id, dimension } = primitiveConstructorNode(
      strandsContext,
      { baseType: BaseType.INT, dimension: 1 },
      indexNode
    );
    index = createStrandsNode(id, dimension, strandsContext);
  }

  // Create a plain object with getters/setters for each struct field.
  // When read, a field creates an ARRAY_ACCESS IR node with the field name encoded
  // in the identifier slot. When written, an ASSIGNMENT IR node is recorded in the CFG.
  const proxy = {};

  for (const field of schema.fields) {
    Object.defineProperty(proxy, field.name, {
      get() {
        // Encode field name in identifier so WGSL backend can emit buf[idx].field
        const nodeData = DAG.createNodeData({
          nodeType: NodeType.OPERATION,
          opCode: OpCode.Binary.ARRAY_ACCESS,
          dependsOn: [bufferNode.id, index.id],
          dimension: field.dim,
          baseType: BaseType.FLOAT,
          identifier: field.name,
        });
        const id = DAG.getOrCreateNode(dag, nodeData);
        CFG.recordInBasicBlock(cfg, cfg.currentBlock, id);
        // When a swizzle assignment fires (e.g. buf[i].vel.y *= -1), onRebind
        // receives the new vector ID and writes it back to the buffer field,
        // equivalent to buf[i].vel = newVec.
        const onRebind = (newFieldID) => {
          const accessData = DAG.createNodeData({
            nodeType: NodeType.OPERATION,
            opCode: OpCode.Binary.ARRAY_ACCESS,
            dependsOn: [bufferNode.id, index.id],
            dimension: field.dim,
            baseType: BaseType.FLOAT,
            identifier: field.name,
          });
          const accessID = DAG.getOrCreateNode(dag, accessData);
          const assignData = DAG.createNodeData({
            nodeType: NodeType.ASSIGNMENT,
            dependsOn: [accessID, newFieldID],
            phiBlocks: [],
          });
          const assignID = DAG.getOrCreateNode(dag, assignData);
          CFG.recordInBasicBlock(cfg, cfg.currentBlock, assignID);
        };
        return createStrandsNode(id, field.dim, strandsContext, onRebind);
      },