Drag to move selection (#28)

src/index.js

@@ -230,6 +230,23 @@ class App extends React.Component {
             const y = e.clientY - e.target.offsetTop;
             const element = newElement(this.state.elementType, x, y);
 
+            let isDraggingElements = false;
+            const cursorStyle = document.documentElement.style.cursor;
+            if (this.state.elementType === "selection") {
+              isDraggingElements = elements.some(el => {
+                if (el.isSelected) {
+                  const minX = Math.min(el.x, el.x + el.width);
+                  const maxX = Math.max(el.x, el.x + el.width);
+                  const minY = Math.min(el.y, el.y + el.height);
+                  const maxY = Math.max(el.y, el.y + el.height);
+                  return minX <= x && x <= maxX && minY <= y && y <= maxY;
+                }
+              });
+              if (isDraggingElements) {
+                document.documentElement.style.cursor = "move";
+              }
+            }
+
             if (this.state.elementType === "text") {
               const text = prompt("What text do you want?");
               if (text === null) {
@@ -263,7 +280,26 @@ class App extends React.Component {
               this.setState({ draggingElement: element });
             }
 
+            let lastX = x;
+            let lastY = y;
+
             const onMouseMove = e => {
+              if (isDraggingElements) {
+                const selectedElements = elements.filter(el => el.isSelected);
+                if (selectedElements.length) {
+                  const x = e.clientX - e.target.offsetLeft;
+                  const y = e.clientY - e.target.offsetTop;
+                  selectedElements.forEach(element => {
+                    element.x += x - lastX;
+                    element.y += y - lastY;
+                  });
+                  lastX = x;
+                  lastY = y;
+                  drawScene();
+                  return;
+                }
+              }
+
               // It is very important to read this.state within each move event,
               // otherwise we would read a stale one!
               const draggingElement = this.state.draggingElement;
@@ -285,15 +321,20 @@ class App extends React.Component {
             const onMouseUp = e => {
               window.removeEventListener("mousemove", onMouseMove);
               window.removeEventListener("mouseup", onMouseUp);
+              document.documentElement.style.cursor = cursorStyle;
 
               const draggingElement = this.state.draggingElement;
               if (draggingElement === null) {
                 return;
               }
               if (this.state.elementType === "selection") {
+                if (isDraggingElements) {
+                  isDraggingElements = false;
+                } else {
                   // Remove actual selection element
-                elements.pop();
                   setSelection(draggingElement);
+                }
+                elements.pop();
               } else {
                 draggingElement.isSelected = true;
               }