Datagrid: Add a public API to get the current viewport

packages/datagrid/src/datagrid.ts

@@ -2012,6 +2012,51 @@ export class DataGrid extends Widget {
     }
   }
 
+  /**
+   * Get the current viewport.
+   *
+   * @returns The current viewport as row/column coordinates.
+   * Returns undefined if the grid is not visible.
+   */
+  get currentViewport(): DataGrid.IBodyRegion | undefined {
+    let width = this.viewport.node.offsetWidth;
+    let height = this.viewport.node.offsetHeight;
+
+    width = Math.round(width);
+    height = Math.round(height);
+
+    if (width <= 0 || height <= 0) {
+      return;
+    }
+
+    const contentW = this._columnSections.length - this.scrollX;
+    const contentH = this._rowSections.length - this.scrollY;
+
+    const contentX = this.headerWidth;
+    const contentY = this.headerHeight;
+
+    const x1 = contentX;
+    const y1 = contentY;
+    const x2 = Math.min(width - 1, contentX + contentW - 1);
+    const y2 = Math.min(height - 1, contentY + contentH - 1);
+
+    const firstRow = this._rowSections.indexOf(y1 - contentY + this.scrollY);
+    const firstColumn = this._columnSections.indexOf(
+      x1 - contentX + this.scrollX
+    );
+    const lastRow = this._rowSections.indexOf(y2 - contentY + this.scrollY);
+    const lastColumn = this._columnSections.indexOf(
+      x2 - contentX + this.scrollX
+    );
+
+    return {
+      firstRow,
+      firstColumn,
+      lastRow,
+      lastColumn
+    };
+  }
+
   /**
    * A message handler invoked on an `'activate-request'` message.
    */
@@ -6721,6 +6766,31 @@ export namespace DataGrid {
     headers: 'none',
     warningThreshold: 1e6
   };
+
+  /**
+   * A body region defined by the cells' boundaries using row/column coordinates.
+   */
+  export interface IBodyRegion {
+    /**
+     * First row of the region
+     */
+    firstRow: number;
+
+    /**
+     * Last row of the region
+     */
+    lastRow: number;
+
+    /**
+     * First column of the region
+     */
+    firstColumn: number;
+
+    /**
+     * Last column of the region
+     */
+    lastColumn: number;
+  }
 }
 
 /**

packages/datagrid/tests/src/datagrid.spec.ts

@@ -0,0 +1,59 @@
+// Copyright (c) Jupyter Development Team.
+// Distributed under the terms of the Modified BSD License.
+import { expect } from 'chai';
+
+import { DataGrid, DataModel } from '@lumino/datagrid';
+
+class LargeDataModel extends DataModel {
+  rowCount(region: DataModel.RowRegion): number {
+    return region === 'body' ? 1_000_000_000_000 : 2;
+  }
+
+  columnCount(region: DataModel.ColumnRegion): number {
+    return region === 'body' ? 1_000_000_000_000 : 3;
+  }
+
+  data(region: DataModel.CellRegion, row: number, column: number): any {
+    if (region === 'row-header') {
+      return `R: ${row}, ${column}`;
+    }
+    if (region === 'column-header') {
+      return `C: ${row}, ${column}`;
+    }
+    if (region === 'corner-header') {
+      return `N: ${row}, ${column}`;
+    }
+    return `(${row}, ${column})`;
+  }
+}
+
+describe('@lumino/datagrid', () => {
+  let datagrid: DataGrid;
+  let model: LargeDataModel;
+
+  beforeEach(() => {
+    datagrid = new DataGrid();
+    model = new LargeDataModel();
+    datagrid.dataModel = model;
+    datagrid.viewport.node.style.height = '500px';
+    datagrid.viewport.node.style.width = '500px';
+    document.children[0].appendChild(datagrid.node);
+  });
+
+  describe('DataGrid', () => {
+    describe('currentViewport()', () => {
+      it('should return the viewport', () => {
+        const viewport = datagrid.currentViewport;
+
+        if (viewport === undefined) {
+          throw new Error('viewport is undefined');
+        }
+
+        expect(viewport.firstRow).to.be.eq(0);
+        expect(viewport.firstColumn).to.be.eq(0);
+        expect(viewport.lastRow).to.be.eq(22);
+        expect(viewport.lastColumn).to.be.eq(4);
+      });
+    });
+  });
+});

packages/datagrid/tests/src/index.spec.ts

@@ -3,3 +3,4 @@
 
 import './textrenderer.spec';
 import './imagerenderer.spec';
+import './datagrid.spec';

review/api/datagrid.api.md

@@ -215,6 +215,7 @@ export class DataGrid extends Widget {
     get copyConfig(): DataGrid.CopyConfig;
     set copyConfig(value: DataGrid.CopyConfig);
     copyToClipboard(): void;
+    get currentViewport(): DataGrid.IBodyRegion | undefined;
     get dataModel(): DataModel | null;
     set dataModel(value: DataModel | null);
     get defaultSizes(): DataGrid.DefaultSizes;
@@ -332,6 +333,12 @@ export namespace DataGrid {
         readonly width: number;
         readonly height: number;
     };
+    export interface IBodyRegion {
+        firstColumn: number;
+        firstRow: number;
+        lastColumn: number;
+        lastRow: number;
+    }
     export interface IKeyHandler extends IDisposable {
         onKeyDown(grid: DataGrid, event: KeyboardEvent): void;
     }
@@ -363,6 +370,10 @@ export namespace DataGrid {
         readonly rowHeaderWidth: number;
         readonly columnHeaderHeight: number;
     };
+    const defaultStyle: Style;
+    const defaultSizes: DefaultSizes;
+    const minimumSizes: MinimumSizes;
+    const defaultCopyConfig: CopyConfig;
     export type Style = {
         readonly voidColor?: string;
         readonly backgroundColor?: string;
@@ -388,10 +399,6 @@ export namespace DataGrid {
             readonly color3: string;
         };
     };
-    const defaultStyle: Style;
-    const defaultSizes: DefaultSizes;
-    const minimumSizes: MinimumSizes;
-    const defaultCopyConfig: CopyConfig;
 }
 
 // @public