Lasso (#586)

* lasso working * break out invert into own function * action * add spatial dimension to crossfilter, in support of polygon lasso * improve comments on new dimension API * lasso vs zoom
2026-09-25 20:48:11 +08:00 · 2019-02-08 11:48:51 -08:00
parent 2e9525741f
commit dbb3a309a9
8 changed files with 564 additions and 146 deletions
@@ -0,0 +1,127 @@
+// https://bl.ocks.org/pbeshai/8008075f9ce771ee8be39e8c38907570
+
+import * as d3 from "d3";
+
+const Lasso = () => {
+  const dispatch = d3.dispatch("start", "end");
+
+  const polygonToPath = polygon =>
+    `M${polygon.map(d => d.join(",")).join("L")}`;
+
+  const distance = (pt1, pt2) =>
+    Math.sqrt((pt2[0] - pt1[0]) ** 2 + (pt2[1] - pt1[1]) ** 2);
+
+  // distance last point has to be to first point before it auto closes when mouse is released
+  const closeDistance = 75;
+
+  const lasso = svg => {
+    let lassoPolygon;
+    let lassoPath;
+    let closePath;
+
+    const handleDragStart = () => {
+      lassoPolygon = [d3.mouse(svg.node())]; // current x y of mouse within element
+
+      if (lassoPath) {
+        lassoPath.remove();
+      }
+
+      lassoPath = g
+        .append("path")
+        .attr("fill", "#0bb")
+        .attr("fill-opacity", 0.1)
+        .attr("stroke", "#0bb")
+        .attr("stroke-dasharray", "3, 3");
+
+      closePath = g
+        .append("line")
+        .attr("x2", lassoPolygon[0][0])
+        .attr("y2", lassoPolygon[0][1])
+        .attr("stroke", "#0bb")
+        .attr("stroke-dasharray", "3, 3")
+        .attr("opacity", 0);
+
+      dispatch.call("start", lasso, lassoPolygon);
+    };
+
+    const handleDrag = () => {
+      const point = d3.mouse(svg.node());
+      lassoPolygon.push(point);
+      lassoPath.attr("d", polygonToPath(lassoPolygon));
+
+      // indicate if we are within closing distance
+      if (
+        distance(lassoPolygon[0], lassoPolygon[lassoPolygon.length - 1]) <
+        closeDistance
+      ) {
+        closePath
+          .attr("x1", point[0])
+          .attr("y1", point[1])
+          .attr("opacity", 1);
+      } else {
+        closePath.attr("opacity", 0);
+      }
+    };
+
+    const handleDragEnd = () => {
+      // remove the close path
+      closePath.remove();
+      closePath = null;
+
+      // succesfully closed
+      if (
+        distance(lassoPolygon[0], lassoPolygon[lassoPolygon.length - 1]) <
+        closeDistance
+      ) {
+        lassoPath.attr("d", `${polygonToPath(lassoPolygon)}Z`);
+        dispatch.call("end", lasso, lassoPolygon);
+
+        // otherwise cancel
+      } else {
+        lassoPath.remove();
+        lassoPath = null;
+        lassoPolygon = null;
+      }
+    };
+
+    // append a <g> with a rect
+    const g = svg.append("g").attr("class", "lasso-group");
+    const bbox = svg.node().getBoundingClientRect();
+    const area = g
+      .append("rect")
+      .attr("width", bbox.width)
+      .attr("height", bbox.height)
+      .attr("fill", "tomato")
+      .attr("opacity", 0);
+
+    const drag = d3
+      .drag()
+      .on("start", handleDragStart)
+      .on("drag", handleDrag)
+      .on("end", handleDragEnd);
+
+    area.call(drag);
+
+    lasso.reset = () => {
+      if (lassoPath) {
+        lassoPath.remove();
+        lassoPath = null;
+      }
+
+      lassoPolygon = null;
+      if (closePath) {
+        closePath.remove();
+        closePath = null;
+      }
+    };
+  };
+
+  lasso.on = (type, callback) => {
+    dispatch.on(type, callback);
+    return lasso;
+  };
+
+  return lasso;
+};
+
+export default Lasso;