Allow rendering geometries to an arbitrary canvas

src/ol/render.js

@@ -0,0 +1,43 @@
+goog.provide('ol.render');
+
+goog.require('goog.vec.Mat4');
+goog.require('ol.render.canvas.Immediate');
+goog.require('ol.vec.Mat4');
+
+
+/**
+ * Binds a Canvas Immediate API to a canvas context, to allow drawing geometries
+ * to the context's canvas.
+ * ```js
+ * 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.drawPolygonGeometry(
+ *     new ol.geom.Polygon([[[0, 0], [100, 100], [100, 0], [0, 0]]]));
+ * ```
+ * Note that {@link ol.render.canvas.Immediate#drawAsync} and
+ * {@link ol.render.canvas.Immediate#drawFeature} cannot be used.
+ *
+ * @param {CanvasRenderingContext2D} context Canvas context.
+ * @param {olx.render.ToContextOptions=} opt_options Options.
+ * @return {ol.render.canvas.Immediate} Canvas Immediate.
+ * @api
+ */
+ol.render.toContext = function(context, opt_options) {
+  var canvas = context.canvas;
+  var options = opt_options ? opt_options : {};
+  var pixelRatio = options.pixelRatio || ol.has.DEVICE_PIXEL_RATIO;
+  var size = options.size;
+  if (size) {
+    canvas.width = size[0] * pixelRatio;
+    canvas.height = size[1] * pixelRatio;
+    canvas.style.width = size[0] + 'px';
+    canvas.style.height = size[1] + 'px';
+  }
+  var extent = [0, 0, canvas.width, canvas.height];
+  var transform = ol.vec.Mat4.makeTransform2D(goog.vec.Mat4.createNumber(),
+      0, 0, pixelRatio, pixelRatio, 0, 0, 0);
+  return new ol.render.canvas.Immediate(context, pixelRatio, extent, transform,
+      0);
+};