函數 toContext

Binds a Canvas Immediate API to a canvas context, to allow drawing geometries to the context's canvas.

The units for geometry coordinates are css pixels relative to the top left corner of the canvas element.

var canvas = document.createElement('canvas');
var render = ol.render.toContext(canvas.getContext('2d'),
    { size: [100, 100] });
render.setFillStrokeStyle(new ol.style.Fill({ color: blue }));
render.drawPolygon(
    new ol.geom.Polygon([[[0, 0], [100, 100], [100, 0], [0, 0]]]));
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