fix: enforce minimum 2x scale on standard displays

Change IMAGE_DOWNLOAD_SCALE from `window.devicePixelRatio || 2` to
`Math.max(window.devicePixelRatio || 1, 2)` so that standard displays
(devicePixelRatio=1) also get 2x output. The previous expression
evaluated to 1 on standard displays since 1 is truthy.

Add tests covering the standard display (dpr=1→2) and zero (dpr=0→2)
cases, and rename the prior fallback test accordingly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: eschutho

superset-frontend/src/utils/downloadAsImage.test.ts

@@ -683,3 +683,148 @@ test('clone path falls back to white background when theme is absent', async ()
 
   document.body.removeChild(container);
 });
+
+test('ag-grid path passes scale option to toJpeg', async () => {
+  jest.useFakeTimers();
+  const { container, agContainer, cleanup } = buildAgGridElement();
+  attachMockApi(agContainer);
+
+  const handler = downloadAsImageOptimized('div', 'My Chart');
+  const exportPromise = handler(syntheticEventFor(container));
+  await jest.runAllTimersAsync();
+  await exportPromise;
+
+  expect(mockToJpeg).toHaveBeenCalledWith(
+    expect.any(HTMLElement),
+    expect.objectContaining({ scale: expect.any(Number) }),
+  );
+
+  cleanup();
+  jest.useRealTimers();
+});
+
+test('clone path passes scale option to toJpeg', async () => {
+  const container = document.createElement('div');
+  document.body.appendChild(container);
+
+  const handler = downloadAsImageOptimized('div', 'Bar Chart');
+  await handler(syntheticEventFor(container));
+
+  expect(mockToJpeg).toHaveBeenCalledWith(
+    expect.any(HTMLElement),
+    expect.objectContaining({ scale: expect.any(Number) }),
+  );
+
+  document.body.removeChild(container);
+});
+
+test('scale uses window.devicePixelRatio when it is a positive number', async () => {
+  let capturedScale: number | undefined;
+
+  await jest.isolateModulesAsync(async () => {
+    Object.defineProperty(window, 'devicePixelRatio', {
+      value: 3,
+      configurable: true,
+    });
+
+    jest.mock('dom-to-image-more', () => ({
+      __esModule: true,
+      default: {
+        toJpeg: jest.fn((_el: HTMLElement, opts: { scale?: number }) => {
+          capturedScale = opts.scale;
+          return Promise.resolve('data:image/jpeg;base64,test');
+        }),
+      },
+    }));
+    jest.mock('src/components/MessageToasts/actions', () => ({
+      addWarningToast: jest.fn(),
+    }));
+    jest.mock('@apache-superset/core/translation', () => ({
+      t: (str: string) => str,
+    }));
+
+    const { default: download } = await import('./downloadAsImage');
+    const container = document.createElement('div');
+    document.body.appendChild(container);
+    await download('div', 'Chart')({ currentTarget: { closest: () => container } } as any);
+    document.body.removeChild(container);
+  });
+
+  expect(capturedScale).toBe(3);
+
+  Object.defineProperty(window, 'devicePixelRatio', {
+    value: 1,
+    configurable: true,
+  });
+});
+
+test('scale enforces a minimum of 2 on standard displays (devicePixelRatio=1)', async () => {
+  let capturedScale: number | undefined;
+
+  await jest.isolateModulesAsync(async () => {
+    Object.defineProperty(window, 'devicePixelRatio', {
+      value: 1,
+      configurable: true,
+    });
+
+    jest.mock('dom-to-image-more', () => ({
+      __esModule: true,
+      default: {
+        toJpeg: jest.fn((_el: HTMLElement, opts: { scale?: number }) => {
+          capturedScale = opts.scale;
+          return Promise.resolve('data:image/jpeg;base64,test');
+        }),
+      },
+    }));
+    jest.mock('src/components/MessageToasts/actions', () => ({
+      addWarningToast: jest.fn(),
+    }));
+    jest.mock('@apache-superset/core/translation', () => ({
+      t: (str: string) => str,
+    }));
+
+    const { default: download } = await import('./downloadAsImage');
+    const container = document.createElement('div');
+    document.body.appendChild(container);
+    await download('div', 'Chart')({ currentTarget: { closest: () => container } } as any);
+    document.body.removeChild(container);
+  });
+
+  // devicePixelRatio=1 is truthy, so || 2 would give 1 — Math.max enforces minimum 2
+  expect(capturedScale).toBe(2);
+});
+
+test('scale enforces a minimum of 2 when devicePixelRatio is 0', async () => {
+  let capturedScale: number | undefined;
+
+  await jest.isolateModulesAsync(async () => {
+    Object.defineProperty(window, 'devicePixelRatio', {
+      value: 0,
+      configurable: true,
+    });
+
+    jest.mock('dom-to-image-more', () => ({
+      __esModule: true,
+      default: {
+        toJpeg: jest.fn((_el: HTMLElement, opts: { scale?: number }) => {
+          capturedScale = opts.scale;
+          return Promise.resolve('data:image/jpeg;base64,test');
+        }),
+      },
+    }));
+    jest.mock('src/components/MessageToasts/actions', () => ({
+      addWarningToast: jest.fn(),
+    }));
+    jest.mock('@apache-superset/core/translation', () => ({
+      t: (str: string) => str,
+    }));
+
+    const { default: download } = await import('./downloadAsImage');
+    const container = document.createElement('div');
+    document.body.appendChild(container);
+    await download('div', 'Chart')({ currentTarget: { closest: () => container } } as any);
+    document.body.removeChild(container);
+  });
+
+  expect(capturedScale).toBe(2);
+});

superset-frontend/src/utils/downloadAsImage.tsx

@@ -25,7 +25,7 @@ import { addWarningToast } from 'src/components/MessageToasts/actions';
 import type { AgGridContainerElement } from '@superset-ui/core/components';
 
 const IMAGE_DOWNLOAD_QUALITY = 0.95;
-const IMAGE_DOWNLOAD_SCALE = window.devicePixelRatio || 2;
+const IMAGE_DOWNLOAD_SCALE = Math.max(window.devicePixelRatio || 1, 2);
 const TRANSPARENT_RGBA = 'transparent';
 const POLL_INTERVAL_MS = 100;