Utilities for polygon renderer

src/ol/render/webgl/webgl.js

@@ -59,3 +59,24 @@ ol.render.webgl.lineStringInstruction = {
   MITER_BOTTOM: 19,
   MITER_TOP: 23
 };
+
+/**
+ * Calcualtes the orientation of a triangle based on the determinant method.
+ * @param {number} x1 First X coordinate.
+ * @param {number} y1 First Y coordinate.
+ * @param {number} x2 Second X coordinate.
+ * @param {number} y2 Second Y coordinate.
+ * @param {number} x3 Third X coordinate.
+ * @param {number} y3 Third Y coordinate.
+ * @return {boolean|undefined} Triangle is clockwise.
+ */
+ol.render.webgl.triangleIsCounterClockwise = function(x1, y1, x2, y2, x3, y3) {
+  var area = (x2 - x1) * (y3 - y1) - (x3 - x1) * (y2 - y1);
+  return area === 0 ? undefined : area > 0;
+};
+
+/**
+ * @const
+ * @type {number}
+ */
+ol.render.webgl.EPSILON = Number.EPSILON || 2.220446049250313e-16;