introduce tags, structs, and reticles

this was meant to be split into smaller changes, but I realised I edited my existing revision too late.

static/haku.js

@@ -113,6 +113,12 @@ export class Pixmap {
     }
 }
 
+// NOTE: This must be kept in sync with ContKind on the haku-wasm side.
+export const ContKind = {
+    Scribble: 0,
+    Dotter: 1,
+};
+
 export class Haku {
     #pInstance = 0;
     #pBrush = 0;
@@ -206,17 +212,49 @@ export class Haku {
         }
     }
 
-    evalBrush() {
-        return this.#statusCodeToResultObject(w.haku_eval_brush(this.#pInstance, this.#pBrush));
+    beginBrush() {
+        return this.#statusCodeToResultObject(w.haku_begin_brush(this.#pInstance, this.#pBrush));
     }
 
-    renderValue(pixmap, translationX, translationY) {
+    expectedContKind() {
+        return w.haku_cont_kind(this.#pInstance);
+    }
+
+    contScribble(pixmap, translationX, translationY) {
         return this.#statusCodeToResultObject(
-            w.haku_render_value(this.#pInstance, pixmap.ptr, translationX, translationY),
+            w.haku_cont_scribble(this.#pInstance, pixmap.ptr, translationX, translationY),
         );
     }
 
-    resetVm() {
-        w.haku_reset_vm(this.#pInstance);
+    contDotter({ fromX, fromY, toX, toY, num }) {
+        return this.#statusCodeToResultObject(
+            w.haku_cont_dotter(this.#pInstance, fromX, fromY, toX, toY, num),
+        );
+    }
+
+    async evalBrush(options) {
+        let { runDotter, runScribble } = options;
+
+        let result;
+        result = this.beginBrush();
+        if (result.status != "ok") return result;
+
+        while (this.expectedContKind() != ContKind.Invalid) {
+            switch (this.expectedContKind()) {
+                case ContKind.Scribble:
+                    result = await runScribble((pixmap, translationX, translationY) => {
+                        return this.contScribble(pixmap, translationX, translationY);
+                    });
+                    return result;
+
+                case ContKind.Dotter:
+                    let dotter = await runDotter();
+                    result = this.contDotter(dotter);
+                    if (result.status != "ok") return result;
+                    break;
+            }
+        }
+
+        return { status: "ok" };
     }
 }