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graph: fix “Download PNG” for large images #1610

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Merged
wchargin merged 1 commit into from
Nov 14, 2018
Merged

graph: fix “Download PNG” for large images #1610

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19 changes: 18 additions & 1 deletion tensorboard/plugins/graph/tf_graph_common/minimap.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -155,7 +155,24 @@ export class Minimap {
let $download = d3.select('#graphdownload');
this.download = <HTMLLinkElement>$download.node();
$download.on('click', d => {
this.download.href = this.downloadCanvas.toDataURL('image/png');
// Revoke the old URL, if any. Then, generate a new URL.
URL.revokeObjectURL(this.download.href);
// We can't use the `HTMLCanvasElement.toBlob` API because it does
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@nfelt nfelt Nov 14, 2018

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FWIW, for the scalar plot download buttons, we use a drop-down menu as the trigger to generate the URL so that it's a two-click process. If we did something similar for the graph it would be possible to use toBlob() and just disable the actual download click target until the synchronous call completes.

Maybe it's not worth it, but I have to imagine toBlob() might be faster than iterating over each character in the blob by hand.

// not have a synchronous variant, and we need to update this href
// synchronously. Instead, we create a blob manually from the data
// URL.
const dataUrl = this.downloadCanvas.toDataURL("image/png");
const prefix = dataUrl.slice(0, dataUrl.indexOf(","));
if (!prefix.endsWith(";base64")) {
console.warn(`non-base64 data URL (${prefix}); cannot use blob download`);
this.download.href = dataUrl;
return;
}
const data = atob(dataUrl.slice(dataUrl.indexOf(",") + 1));
const bytes =
new Uint8Array(data.length).map((_, i) => data.charCodeAt(i));
const blob = new Blob([bytes], {type: "image/png"});
this.download.href = URL.createObjectURL(blob);
});

let $svg = d3.select(this.svg);
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