fix(grid): keep canvas backing store at observed pixel density under reduced UI scale

apps/desktop/src/lib/__tests__/dataGrid/canvasDataGridRendererFrozen.spec.ts

@@ -97,6 +97,17 @@ describe("drawCanvasDataGrid with frozen columns", () => {
     });
   });
 
+  it.each([1, 1.125, 1.1875, 1.2345])("keeps the exact observed density when the nominal ratio is %s", (pixelRatio) => {
+    expect(
+      resolveCanvasBackingStoreMetrics({
+        width: 800,
+        height: 400,
+        pixelRatio,
+        devicePixelSize: { cssWidth: 800, cssHeight: 400, pixelWidth: 1000, pixelHeight: 500 },
+      }),
+    ).toEqual({ pixelWidth: 1000, pixelHeight: 500, scaleX: 1.25, scaleY: 1.25, measured: true });
+  });
+
   it("ignores a stale observed size after the CSS viewport changes", () => {
     expect(
       resolveCanvasBackingStoreMetrics({
@@ -108,17 +119,21 @@ describe("drawCanvasDataGrid with frozen columns", () => {
     ).toEqual({ pixelWidth: 1125, pixelHeight: 500, scaleX: 1.25, scaleY: 1.25, measured: false });
   });
 
-  it("caps the observed backing store at the configured pixel ratio", () => {
+  it("caps the observed backing store only at the absolute safety limit", () => {
     expect(
       resolveCanvasBackingStoreMetrics({
         width: 801,
         height: 399,
-        pixelRatio: 4,
+        pixelRatio: 1.125,
         devicePixelSize: { cssWidth: 801, cssHeight: 399, pixelWidth: 4005, pixelHeight: 1995 },
       }),
     ).toEqual({ pixelWidth: 3204, pixelHeight: 1596, scaleX: 4, scaleY: 4, measured: true });
   });
 
+  it("caps a fallback ratio at the absolute safety limit", () => {
+    expect(resolveCanvasBackingStoreMetrics({ width: 801, height: 399, pixelRatio: 5 })).toEqual({ pixelWidth: 3204, pixelHeight: 1596, scaleX: 4, scaleY: 4, measured: false });
+  });
+
   it("draws without errors when frozenColumnCount is 0", () => {
     const canvas = createMockCanvas();
     const options = createBaseOptions({ canvas, frozenColumnCount: 0 });

apps/desktop/src/lib/dataGrid/canvasDataGridRenderer.ts

@@ -3,6 +3,7 @@ import type { RowStatus } from "@/lib/dataGrid/gridRowStatus";
 import { DATA_GRID_DARK_SEARCH_COLORS, resolveDataGridPaintTheme, type DataGridPaintTheme } from "@/lib/dataGrid/dataGridPaintTheme";
 
 export const CANVAS_DATA_GRID_ROW_HEIGHT = 26;
+export const MAX_CANVAS_DATA_GRID_PIXEL_RATIO = 4;
 
 export interface CanvasDevicePixelSize {
   cssWidth: number;
@@ -111,13 +112,15 @@ export interface CanvasBackingStoreMetrics {
 export function resolveCanvasBackingStoreMetrics(options: { width: number; height: number; pixelRatio: number; devicePixelSize?: CanvasDevicePixelSize | null }): CanvasBackingStoreMetrics {
   const width = Math.max(1, options.width);
   const height = Math.max(1, options.height);
-  const fallbackRatio = Math.max(1, options.pixelRatio);
+  const fallbackRatio = Math.min(MAX_CANVAS_DATA_GRID_PIXEL_RATIO, Math.max(1, options.pixelRatio));
   const measured = options.devicePixelSize;
   const measurementMatches = !!measured && Math.abs(measured.cssWidth - width) <= 0.5 && Math.abs(measured.cssHeight - height) <= 0.5 && measured.pixelWidth > 0 && measured.pixelHeight > 0;
   const fallbackPixelWidth = Math.max(1, Math.ceil(width * fallbackRatio));
   const fallbackPixelHeight = Math.max(1, Math.ceil(height * fallbackRatio));
-  const pixelWidth = measurementMatches ? Math.min(measured.pixelWidth, fallbackPixelWidth) : fallbackPixelWidth;
-  const pixelHeight = measurementMatches ? Math.min(measured.pixelHeight, fallbackPixelHeight) : fallbackPixelHeight;
+  const maxPixelWidth = Math.max(1, Math.ceil(width * MAX_CANVAS_DATA_GRID_PIXEL_RATIO));
+  const maxPixelHeight = Math.max(1, Math.ceil(height * MAX_CANVAS_DATA_GRID_PIXEL_RATIO));
+  const pixelWidth = measurementMatches ? Math.min(measured.pixelWidth, maxPixelWidth) : fallbackPixelWidth;
+  const pixelHeight = measurementMatches ? Math.min(measured.pixelHeight, maxPixelHeight) : fallbackPixelHeight;
   return {
     pixelWidth,
     pixelHeight,