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fix: combine repeated chart exports into single image #492

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fix: combine repeated chart exports into single image #492

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78 changes: 66 additions & 12 deletions packages/graphic-walker/src/utils/vegaApiExport.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,56 @@ import { useAppRootContext } from "../components/appRoot";
import type { IReactVegaHandler } from "../vis/react-vega";
import type { IChartExportResult, IVegaChartRef } from "../interfaces";

function concatCanvases(canvases: HTMLCanvasElement[], refs: IVegaChartRef[]) {
if (canvases.length === 0) {
return null;
}

if (canvases.length === 1) {
return canvases[0];
}

const columnCount = refs.reduce((max, current) => Math.max(max, current.x), 0) + 1;
const rowCount = refs.reduce((max, current) => Math.max(max, current.y), 0) + 1;
const colWidths = new Array(columnCount).fill(0);
const rowHeights = new Array(rowCount).fill(0);

canvases.forEach((canvas, idx) => {
const ref = refs[idx];
colWidths[ref.x] = Math.max(colWidths[ref.x], canvas.width);
rowHeights[ref.y] = Math.max(rowHeights[ref.y], canvas.height);
});

const colOffsets: number[] = [];
const rowOffsets: number[] = [];
colWidths.reduce((offset, width, index) => {
colOffsets[index] = offset;
return offset + width;
}, 0);
rowHeights.reduce((offset, height, index) => {
rowOffsets[index] = offset;
return offset + height;
}, 0);

const mergedCanvas = document.createElement('canvas');
mergedCanvas.width = colWidths.reduce((sum, width) => sum + width, 0);
mergedCanvas.height = rowHeights.reduce((sum, height) => sum + height, 0);

const ctx = mergedCanvas.getContext('2d');
if (!ctx) {
return null;
}

canvases.forEach((canvas, idx) => {
const ref = refs[idx];
const x = colOffsets[ref.x];
const y = rowOffsets[ref.y];
ctx.drawImage(canvas, x, y, canvas.width, canvas.height);
});

return mergedCanvas;
}


export const useVegaExportApi = (
name: string | undefined,
Expand All @@ -27,7 +77,11 @@ export const useVegaExportApi = (
}
return item.view.toCanvas(2);
}));
return canvases.map(canvas => canvas.toDataURL('image/png', 1));
const merged = concatCanvases(canvases, viewsRef.current);
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@cursor cursor Bot Dec 5, 2025

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Bug: Stale ref used after async canvas generation

In getCanvasData() and downloadPNG(), viewsRef.current is read once before the async Promise.all() to generate canvases, then read again after the await to pass to concatCanvases. If viewsRef.current changes during the async operation (e.g., due to re-render), the canvases array and refs array could have different lengths or orderings, causing concatCanvases to access undefined ref elements and throw a TypeError when accessing ref.x or ref.y.

Additional Locations (1)

Fix in Cursor Fix in Web

if (!merged) {
return [];
}
return [merged.toDataURL('image/png', 1)];
},
async downloadSVG(filename = `gw chart ${Date.now() % 1_000_000}`.padStart(6, '0')) {
const data = await Promise.all(viewsRef.current.map(item => {
Expand Down Expand Up @@ -58,16 +112,16 @@ export const useVegaExportApi = (
}
return item.view.toCanvas(2);
}));
const data = canvases.map(canvas => canvas.toDataURL('image/png', 1));
const files: string[] = [];
for (let i = 0; i < data.length; i += 1) {
const d = data[i];
const a = document.createElement('a');
a.download = `${filename}${data.length > 1 ? `_${i + 1}` : ''}.png`;
a.href = d.replace(/^data:image\/[^;]/, 'data:application/octet-stream');
a.click();
const merged = concatCanvases(canvases, viewsRef.current);
if (!merged) {
return [];
}
return files;
const data = merged.toDataURL('image/png', 1);
const a = document.createElement('a');
a.download = `${filename}.png`;
a.href = data.replace(/^data:image\/[^;]/, 'data:application/octet-stream');
a.click();
return [data];
},
};

Expand Down Expand Up @@ -177,8 +231,8 @@ export const useVegaExportApi = (
if (mode === 'data-url') {
const imgData = await renderHandle.getCanvasData();
if (imgData) {
for (let i = 0; i < imgData.length; i += 1) {
res.charts[i].data = imgData[i];
for (let i = 0; i < res.charts.length; i += 1) {
res.charts[i].data = imgData[Math.min(i, imgData.length - 1)] ?? '';
}
}
} else if (mode === 'svg') {
Expand Down