[oden] Writable Textures and re-work TS API

Now we return Texture objects to make things a little bit more
type-safe, at the cost of a small allocation (I hope!)

src/graphics.ts

@@ -52,6 +52,16 @@ export function spr(
   core.spr(x, y, w, h, sx, sy, sw, sh);
 }
 
+export class Texture {
+  #id: number;
+  constructor(id: number) {
+    this.#id = id;
+  }
+  id(): number {
+    return this.#id;
+  }
+}
+
 /**
  * Create a texture based on the loaded buffer.
  *
@@ -61,15 +71,41 @@ export function spr(
 export function create_texture(
   buffer: ArrayBuffer,
   label: string | undefined = undefined
-): number {
-  return core.create_texture(buffer, label);
+): Texture {
+  const id = core.create_texture(buffer, label);
+  return new Texture(id);
 }
 
 /**
  * Set the specified texture as the current texture for calls to e.g. spr().
  *
- * @param id - The identifier of the texture to use.
+ * @param texture - The texture to use.
  */
-export function use_texture(id: number) {
-  core.use_texture(id);
+export function use_texture(id: Texture) {
+  core.use_texture(id.id());
+}
+
+/**
+ * Create a texture that we can render to.
+ */
+export function create_writable_texture(
+  width: number,
+  height: number,
+  label: string | undefined = undefined
+): Texture {
+  return new Texture(core.create_writable_texture(width, height, label));
+}
+
+/**
+ * Set the current render target to the screen.
+ */
+export function write_to_screen() {
+  core.write_to_screen();
+}
+
+/**
+ * Set the current render target to the specified texture.
+ */
+export function write_to_texture(texture: Texture) {
+  core.write_to_texture(texture.id());
 }