StackGenVis: Alignment of Data, Algorithms, and Models for Stacking Ensemble Learning Using Performance Metrics
https://doi.org/10.1109/TVCG.2020.3030352
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37 lines
3.6 KiB
37 lines
3.6 KiB
# vega-canvas
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[Canvas](https://developer.mozilla.org/en-US/docs/Web/API/Canvas_API) and [Image](https://developer.mozilla.org/en-US/docs/Web/API/HTMLImageElement/Image) object instantiation utilities. Creates an [HTML5 Canvas](https://developer.mozilla.org/en-US/docs/Web/API/Canvas_API), using either the web browser DOM or a [node-canvas](https://github.com/Automattic/node-canvas) library.
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This package attempts three forms of canvas creation, in this order:
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- If in a browser environment, use DOM methods to create a new canvas.
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- If the [node-canvas](https://github.com/Automattic/node-canvas) library is present, use that.
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- Otherwise, return `null`.
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To ensure error-free build processes for client-side code, this module does not include any direct or optional dependencies on the [node-canvas](https://github.com/Automattic/node-canvas) library. Projects that use this pacakge and require canvas support for server-side (node.js) operations *must include a canvas dependency in their own `package.json` file*.
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## API Reference
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<a name="canvas" href="#canvas">#</a>
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vega.<b>canvas</b>([<i>width</i>, <i>height</i>, <i>type</i>])
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[<>](https://github.com/vega/vega/blob/master/packages/vega-canvas/index.js "Source")
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Creates a new [Canvas](https://developer.mozilla.org/en-US/docs/Web/API/Canvas_API) instance, with an optional *width* and *height* (in pixels). If *width* and *height* are omitted, creates a _0 x 0_ canvas. The optional *type* parameter is a [node-canvas type parameter](https://github.com/Automattic/node-canvas#createcanvas) to enable PDF or SVG output modes; this parameter is applied only if node-canvas is used. This method first attempts to create a canvas using the DOM `document.createElement` method. If that fails, the method then attempts to instantiate a canvas using the [node-canvas](https://github.com/Automattic/node-canvas) library. If that also fails, returns `null`.
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<a name="domCanvas" href="#domCanvas">#</a>
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vega.<b>domCanvas</b>([<i>width</i>, <i>height</i>])
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[<>](https://github.com/vega/vega/blob/master/packages/vega-canvas/src/domCanvas.js "Source")
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Creates a new [Canvas](https://developer.mozilla.org/en-US/docs/Web/API/Canvas_API) instance, with an optional *width* and *height* (in pixels). If *width* and *height* are omitted, creates a _0 x 0_ canvas. This method first attempts to create a canvas using the DOM `document.createElement` method. If that fails, returns `null`.
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<a name="nodeCanvas" href="#nodeCanvas">#</a>
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vega.<b>nodeCanvas</b>([<i>width</i>, <i>height</i>, <i>type</i>])
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[<>](https://github.com/vega/vega/blob/master/packages/vega-canvas/src/nodeCanvas.js "Source")
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Creates a new [Canvas](https://developer.mozilla.org/en-US/docs/Web/API/Canvas_API) instance, with an optional *width* and *height* (in pixels). If *width* and *height* are omitted, creates a _0 x 0_ canvas. The optional *type* parameter is a [node-canvas type parameter](https://github.com/Automattic/node-canvas#createcanvas) to enable PDF or SVG output modes. This method attempts to instantiate a canvas using using the [node-canvas](https://github.com/Automattic/node-canvas) library. If that fails, returns `null`. This method is not exported in browser-only builds.
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<a name="image" href="#image">#</a>
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vega.<b>image</b>()
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[<>](https://github.com/vega/vega/blob/master/packages/vega-canvas/index.js "Source")
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Returns a reference to the [Image](https://developer.mozilla.org/en-US/docs/Web/API/HTMLImageElement/Image) constructor. In a web browser environment, simply returns the built-in `Image` object. Otherwise, attempts to return the `Image` instance exported by a node canvas library. If all attempts to find a canvas library fail, returns `null`.
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