✨ add RenderInfo with lazy element bounds lookup

Adds an `info: RenderInfo` field to RenderResult that provides
on-demand access to element bounding boxes after layout. Callers
query by element id via `info.get(id)`, which calls into WASM to
hash the id and look up the computed bounds via Clay_GetElementData().

A single WASM export handles the lookup — no tables or globals.
Uses the typedef struct infrastructure for BoundingBox field offsets.

Author: cowboyd

specs/renderer-spec.md

@@ -631,7 +631,7 @@ prevent overlap.
 ### 12.3 Render return type
 
 The `render()` method currently returns a `RenderResult` object shaped as
-`{ output: Uint8Array, events: PointerEvent[] }`.
+`{ output: Uint8Array, events: PointerEvent[], info: RenderInfo }`.
 
 The `output` field is the ANSI byte output specified normatively in Section 7.3
 and Section 8.2.
@@ -643,6 +643,34 @@ but has acknowledged gaps (no modifier keys on click events) and its interaction
 protocol (passing pointer state via render options, then reading events from the
 return value) was arrived at through iteration rather than upfront design.
 
+The `info` field implements `RenderInfo`, a read-only lookup keyed by element id
+(the `id` parameter passed to `open()`):
+
+```
+interface RenderInfo {
+  get(id: string): ElementInfo | undefined;
+}
+
+interface ElementInfo {
+  bounds: BoundingBox;
+}
+
+interface BoundingBox {
+  x: number;
+  y: number;
+  width: number;
+  height: number;
+}
+```
+
+Each `ElementInfo` provides post-layout metadata. The `bounds` field is the
+element's computed bounding box in character cells, as determined by the layout
+engine after the render transaction completes. `x` and `y` are zero-indexed from
+the top-left corner of the layout root.
+
+Querying an element with an empty-string id or an id not present in the frame
+returns `undefined`.
+
 The return type of `render()` has changed twice since the project's inception
 (string, then `Uint8Array`, then `RenderResult`). While the ANSI bytes
 commitment (Section 7.3) is stable, the wrapper shape around those bytes is not.

src/clayterm.c

@@ -611,6 +611,20 @@ char *output(struct Clayterm *ct) { return ct->out.data; }
 
 int length(struct Clayterm *ct) { return ct->out.length; }
 
+int get_element_bounds(const char *name, int name_len, float *out) {
+  Clay_String str = {.length = name_len, .chars = name};
+  Clay_ElementId eid = Clay__HashString(str, 0);
+  Clay_ElementData data = Clay_GetElementData(eid);
+  if (!data.found) {
+    return 0;
+  }
+  out[0] = data.boundingBox.x;
+  out[1] = data.boundingBox.y;
+  out[2] = data.boundingBox.width;
+  out[3] = data.boundingBox.height;
+  return 1;
+}
+
 int pointer_over_count(void) { return Clay_GetPointerOverIds().length; }
 
 int pointer_over_id_string_length(int index) {

src/clayterm.h

@@ -17,6 +17,8 @@ char *output(struct Clayterm *ct);
 int length(struct Clayterm *ct);
 void measure(int ret, int txt);
 
+int get_element_bounds(const char *name, int name_len, float *out);
+
 int pointer_over_count(void);
 int pointer_over_id_string_length(int index);
 int pointer_over_id_string_ptr(int index);

term-native.ts

@@ -1,3 +1,21 @@
+import { f32, offsets, struct } from "./typedef.ts";
+
+export interface BoundingBox {
+  x: number;
+  y: number;
+  width: number;
+  height: number;
+}
+
+const BoundingBoxStruct = struct<BoundingBox>({
+  x: f32(),
+  y: f32(),
+  width: f32(),
+  height: f32(),
+});
+
+const BOUNDING_BOX = offsets(BoundingBoxStruct);
+
 export interface Native {
   memory: WebAssembly.Memory;
   statePtr: number;
@@ -7,6 +25,7 @@ export interface Native {
   length(ct: number): number;
   setPointer(x: number, y: number, down: boolean): void;
   getPointerOverIds(): string[];
+  getElementBounds(id: string): BoundingBox | undefined;
 }
 
 import { compiled } from "./wasm.ts";
@@ -60,6 +79,7 @@ export async function createTermNative(
     pointer_over_count(): number;
     pointer_over_id_string_length(index: number): number;
     pointer_over_id_string_ptr(index: number): number;
+    get_element_bounds(name: number, len: number, out: number): number;
   };
 
   let heap = ct.__heap_base.value as number;
@@ -101,5 +121,22 @@ export async function createTermNative(
       }
       return ids;
     },
+    getElementBounds(id: string): BoundingBox | undefined {
+      let enc = new TextEncoder();
+      let bytes = enc.encode(id);
+      new Uint8Array(memory.buffer).set(bytes, opsBuf);
+      let out = opsBuf + 256;
+      let found = ct.get_element_bounds(opsBuf, bytes.length, out);
+      if (!found) {
+        return undefined;
+      }
+      let view = new DataView(memory.buffer);
+      return {
+        x: view.getFloat32(out + BOUNDING_BOX.x, true),
+        y: view.getFloat32(out + BOUNDING_BOX.y, true),
+        width: view.getFloat32(out + BOUNDING_BOX.width, true),
+        height: view.getFloat32(out + BOUNDING_BOX.height, true),
+      };
+    },
   };
 }

term.ts

@@ -1,5 +1,5 @@
 import { type Op, pack } from "./ops.ts";
-import { createTermNative } from "./term-native.ts";
+import { type BoundingBox, createTermNative } from "./term-native.ts";
 
 export interface TermOptions {
   height: number;
@@ -32,9 +32,20 @@ export type PointerEvent =
   | { type: "pointerleave"; id: string }
   | { type: "pointerclick"; id: string };
 
+export type { BoundingBox };
+
+export interface ElementInfo {
+  bounds: BoundingBox;
+}
+
+export interface RenderInfo {
+  get(id: string): ElementInfo | undefined;
+}
+
 export interface RenderResult {
   output: Uint8Array;
   events: PointerEvent[];
+  info: RenderInfo;
 }
 
 export interface Term {
@@ -103,7 +114,17 @@ export async function createTerm(options: TermOptions): Promise<Term> {
       prev = current;
       wasDown = down;
 
-      return { output, events };
+      let info: RenderInfo = {
+        get(id: string): ElementInfo | undefined {
+          let bounds = native.getElementBounds(id);
+          if (bounds) {
+            return { bounds };
+          }
+          return undefined;
+        },
+      };
+
+      return { output, events, info };
     },
   };
 }

test/term.test.ts

@@ -1,6 +1,6 @@
 import { beforeEach, describe, expect, it } from "./suite.ts";
 import { createTerm, type Term } from "../term.ts";
-import { close, grow, open, rgba, text } from "../ops.ts";
+import { close, fixed, grow, open, rgba, text } from "../ops.ts";
 import { print } from "./print.ts";
 
 const decode = (bytes: Uint8Array) => new TextDecoder().decode(bytes);
@@ -151,6 +151,46 @@ describe("term", () => {
     });
   });
 
+  describe("info", () => {
+    it("returns bounds for named elements", async () => {
+      let term = await createTerm({ width: 40, height: 10 });
+      let result = term.render([
+        open("root", {
+          layout: { width: grow(), height: grow(), direction: "ttb" },
+        }),
+        open("child", {
+          layout: { width: fixed(20), height: fixed(5) },
+        }),
+        close(),
+        close(),
+      ]);
+
+      let root = result.info.get("root");
+      expect(root).toBeDefined();
+      expect(root!.bounds).toEqual({ x: 0, y: 0, width: 40, height: 10 });
+
+      let child = result.info.get("child");
+      expect(child).toBeDefined();
+      expect(child!.bounds).toEqual({ x: 0, y: 0, width: 20, height: 5 });
+    });
+
+    it("returns undefined for unknown ids", async () => {
+      let term = await createTerm({ width: 20, height: 5 });
+      term.render([
+        open("root", { layout: { width: grow(), height: grow() } }),
+        close(),
+      ]);
+
+      let result = term.render([
+        open("root", { layout: { width: grow(), height: grow() } }),
+        close(),
+      ]);
+
+      expect(result.info.get("nonexistent")).toBeUndefined();
+      expect(result.info.get("")).toBeUndefined();
+    });
+  });
+
   describe("row offset", () => {
     it("renders two frames at the offset position", async () => {
       let term = await createTerm({ width: 20, height: 5 });

typedef.ts

@@ -56,6 +56,11 @@ export function array<T>(element: TypeDef<T>, length: number): Arr<T[]> {
   };
 }
 
+export const f32 = (): TypeDef<number> => ({
+  type: "f32",
+  byteLength: 4,
+  byteAlign: 4,
+});
 export const int32 = (): TypeDef<number> => ({
   type: "int32",
   byteLength: 4,