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add description of WebGLDrawer drawing pipeline

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Tom 2024-01-11 13:54:01 -05:00
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commit e0fd78344b
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src/webgldrawer.js
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@ -38,7 +38,17 @@
/**
* @class WebGLDrawer
* @memberof OpenSeadragon
* @classdesc Default implementation of WebGLDrawer for an {@link OpenSeadragon.Viewer}.
* @classdesc Default implementation of WebGLDrawer for an {@link OpenSeadragon.Viewer}. The WebGLDrawer
* loads tile data as textures to the graphics card as soon as it is available (via the tile-ready event),
* and unloads the data (via the image-unloaded event). The drawer utilizes a context-dependent two pass drawing pipeline.
* For the first pass, tile composition for a given TiledImage is always done using a canvas with a WebGL context.
* This allows tiles to be stitched together without seams or artifacts, without requiring a tile source with overlap. If overlap is present,
* overlapping pixels are discarded. The second pass copies all pixel data from the WebGL context onto an output canvas
* with a Context2d context. This allows appliations to have access to pixel data and other functionality provided by
* Context2d, regardless of whether the CanvasDrawer or the WebGLDrawer is used. Certain options, including compositeOperation,
* clip, croppingPolygons, and debugMode are implemented using Context2d operations; in these scenarios, each TiledImage is
* drawn onto the output canvas immediately after the tile composition step (pass 1). Otherwise, for efficiency, all TiledImages
* are copied over to the output canvas at once, after all tiles have been composited for all images.
* @param {Object} options - Options for this Drawer.
* @param {OpenSeadragon.Viewer} options.viewer - The Viewer that owns this Drawer.
* @param {OpenSeadragon.Viewport} options.viewport - Reference to Viewer viewport.