Implement native opening scenes, battle foundation and overworld movement

tests/viewport.test.ts

@@ -0,0 +1,56 @@
+import { describe, expect, it } from "vitest";
+import {
+  BASE_VIEWPORT,
+  MAX_VIEWPORT,
+  renderViewportForBox,
+} from "../src/game/rendering/viewport";
+
+describe("adaptive native viewport", () => {
+  it("keeps detached fixture canvases at the original resolution", () => {
+    expect(renderViewportForBox(0, 0)).toEqual({
+      ...BASE_VIEWPORT,
+      pixelScale: 3,
+    });
+    expect(renderViewportForBox(Number.NaN, 500)).toEqual({
+      ...BASE_VIEWPORT,
+      pixelScale: 3,
+    });
+  });
+
+  it("uses one integer scale on both axes and reveals additional world", () => {
+    const phone = renderViewportForBox(390, 720);
+    expect(phone).toEqual({ width: 195, height: 360, pixelScale: 2 });
+
+    const desktop = renderViewportForBox(960, 648);
+    expect(desktop).toEqual({ width: 320, height: 216, pixelScale: 3 });
+    expect(desktop.width).toBeGreaterThan(BASE_VIEWPORT.width);
+    expect(desktop.height).toBeGreaterThan(BASE_VIEWPORT.height);
+    expect(desktop.width * desktop.pixelScale).toBe(960);
+    expect(desktop.height * desktop.pixelScale).toBe(648);
+  });
+
+  it("rounds fractional boxes without materially changing their aspect", () => {
+    const css = { width: 713.5, height: 481.25 };
+    const viewport = renderViewportForBox(css.width, css.height);
+    expect(
+      Math.abs(viewport.width / viewport.height - css.width / css.height),
+    ).toBeLessThan(0.005);
+  });
+
+  it.each([
+    [304, 400],
+    [844, 220],
+    [1920, 600],
+    [100_000, 100_000],
+  ])(
+    "preserves the aspect of a %d x %d box while bounding buffers",
+    (width, height) => {
+      const viewport = renderViewportForBox(width, height);
+      expect(viewport.width).toBeLessThanOrEqual(MAX_VIEWPORT.width);
+      expect(viewport.height).toBeLessThanOrEqual(MAX_VIEWPORT.height);
+      expect(
+        Math.abs(viewport.width / viewport.height - width / height),
+      ).toBeLessThan(0.03);
+    },
+  );
+});