Function drawArrow

src/components/annotations/draw.js:500–645

(dx, dy)

         * while the head stays put, dx and dy are the pixel offsets
         */
        var drawArrow = function(dx, dy) {
            annGroup
                .selectAll('.annotation-arrow-g')
                .remove();

            var headX = annPosPx.x.head;
            var headY = annPosPx.y.head;
            var tailX = annPosPx.x.tail + dx;
            var tailY = annPosPx.y.tail + dy;
            var textX = annPosPx.x.text + dx;
            var textY = annPosPx.y.text + dy;

            // find the edge of the text box, where we'll start the arrow:
            // create transform matrix to rotate the text box corners
            var transform = Lib.rotationXYMatrix(textangle, textX, textY);
            var applyTransform = Lib.apply2DTransform(transform);
            var applyTransform2 = Lib.apply2DTransform2(transform);

            // calculate and transform bounding box
            var width = +annTextBG.attr('width');
            var height = +annTextBG.attr('height');
            var xLeft = textX - 0.5 * width;
            var xRight = xLeft + width;
            var yTop = textY - 0.5 * height;
            var yBottom = yTop + height;
            var edges = [
                [xLeft, yTop, xLeft, yBottom],
                [xLeft, yBottom, xRight, yBottom],
                [xRight, yBottom, xRight, yTop],
                [xRight, yTop, xLeft, yTop]
            ].map(applyTransform2);

            // Remove the line if it ends inside the box.  Use ray
            // casting for rotated boxes: see which edges intersect a
            // line from the arrowhead to far away and reduce with xor
            // to get the parity of the number of intersections.
            if(edges.reduce(function(a, x) {
                return a ^
                    !!Lib.segmentsIntersect(headX, headY, headX + 1e6, headY + 1e6,
                            x[0], x[1], x[2], x[3]);
            }, false)) {
                // no line or arrow - so quit drawArrow now
                return;
            }

            edges.forEach(function(x) {
                var p = Lib.segmentsIntersect(tailX, tailY, headX, headY,
                            x[0], x[1], x[2], x[3]);
                if(p) {
                    tailX = p.x;
                    tailY = p.y;
                }
            });

            var strokewidth = options.arrowwidth;
            var arrowColor = options.arrowcolor;
            var arrowSide = options.arrowside;