Add subtraction mode

Author: dy

src/lib/polygon.js

@@ -186,6 +186,7 @@ polygon.multitester = function multitester(list) {
 
     for(var i = 0; i < list.length; i++) {
         var tester = polygon.tester(list[i]);
+        tester.subtract = list[i].subtract;
         testers.push(tester);
         xmin = Math.min(xmin, tester.xmin);
         xmax = Math.max(xmax, tester.xmax);
@@ -194,10 +195,15 @@ polygon.multitester = function multitester(list) {
     }
 
     function contains(pt, arg) {
+        var yes = false;
         for(var i = 0; i < testers.length; i++) {
-            if(testers[i].contains(pt, arg)) return true;
+            if(testers[i].contains(pt, arg)) {
+                // if contained by subtract polygon - exclude the point
+                yes = testers[i].subtract === false;
+            }
         }
-        return false;
+
+        return yes;
     }
 
     return {

src/plots/cartesian/dragbox.js

@@ -173,15 +173,15 @@ module.exports = function dragBox(gd, plotinfo, x, y, w, h, ns, ew) {
                 dragOptions.yaxes = ya;
 
                 // take over selection polygons from prev mode, if any
-                if(e.shiftKey && plotinfo.selection.polygons && !dragOptions.polygons) {
+                if((e.shiftKey || e.altKey) && plotinfo.selection.polygons && !dragOptions.polygons) {
                     dragOptions.polygons = plotinfo.selection.polygons;
                     dragOptions.mergedPolygons = plotinfo.selection.mergedPolygons;
                 }
                 // create new polygons, if shift mode
-                else if(!e.shiftKey || (e.shiftKey && !plotinfo.selection.polygons)) {
+                else if((!e.shiftKey && !e.altKey) || ((e.shiftKey || e.altKey) && !plotinfo.selection.polygons)) {
                     plotinfo.selection = {};
                     plotinfo.selection.polygons = dragOptions.polygons = [];
-                    dragOptions.mergedPolygons = plotinfo.selection.mergedPolygons = [];
+                    plotinfo.selection.mergedPolygons = dragOptions.mergedPolygons = [];
                 }
 
                 prepSelect(e, startX, startY, dragOptions, dragModeNow);

src/plots/cartesian/select.js

@@ -41,7 +41,8 @@ module.exports = function prepSelect(e, startX, startY, dragOptions, mode) {
         xAxisIds = dragOptions.xaxes.map(getAxId),
         yAxisIds = dragOptions.yaxes.map(getAxId),
         allAxes = dragOptions.xaxes.concat(dragOptions.yaxes),
-        filterPoly, testPoly, mergedPolygons, currentPolygon;
+        filterPoly, testPoly, mergedPolygons, currentPolygon,
+        subtract = e.altKey;
 
     if(mode === 'lasso') {
         filterPoly = filteredPolygon([[x0, y0]], constants.BENDPX);
@@ -193,7 +194,8 @@ module.exports = function prepSelect(e, startX, startY, dragOptions, mode) {
 
         // create outline & tester
         if(dragOptions.polygons && dragOptions.polygons.length) {
-            mergedPolygons = joinPolygons(dragOptions.mergedPolygons, currentPolygon);
+            mergedPolygons = mergePolygons(dragOptions.mergedPolygons, currentPolygon, subtract);
+            currentPolygon.subtract = subtract;
             testPoly = multipolygonTester(dragOptions.polygons.concat([currentPolygon]));
         }
         else {
@@ -262,6 +264,7 @@ module.exports = function prepSelect(e, startX, startY, dragOptions, mode) {
 
             if(currentPolygon && dragOptions.polygons) {
                 // save last polygons
+                currentPolygon.subtract = subtract;
                 dragOptions.polygons.push(currentPolygon);
 
                 // we have to keep reference to arrays container
@@ -272,8 +275,22 @@ module.exports = function prepSelect(e, startX, startY, dragOptions, mode) {
     };
 };
 
-function joinPolygons(list, poly) {
-    var res = polybool.union({
+function mergePolygons(list, poly, subtract) {
+    var res;
+
+    if(subtract) {
+        res = polybool.difference({
+            regions: list,
+            inverted: false
+        }, {
+            regions: [poly],
+            inverted: false
+        });
+
+        return res.regions;
+    }
+
+    res = polybool.union({
         regions: list,
         inverted: false
     }, {