Fix a couple of issues seen in review.

Return true from the sineWaveTool updateHighlights method so that the
general graphtool move handler doesn't overrided the coordinates set in
the updateHighlights method.

During the sine wave tool graphing phases instead of refusing to plot a
point when a down event occurs and the cursor is in an invalid location,
just plot the point where the highlight point currently is. Refusing to
plot the point can be confusing because the highlight point looks like
it is where the user wants it to be, and yet the click does nothing.
This technique needs to be implemented for all of the tools. It is
better than the previous method since it is more intuitive for the user.

htdocs/js/GraphTool/sinewavetool.js

@@ -225,8 +225,8 @@
 				this.supportsSolidDash = true;
 
 				this.phase1 = (coords) => {
-					// Don't allow the point to be created off the board.
-					if (!gt.boardHasPoint(coords[1], coords[2])) return;
+					// If the current coordinates are off the board, then use the highlight point coordinates instead.
+					if (!gt.boardHasPoint(coords[1], coords[2])) coords = this.hlObjs.hl_point.coords.usrCoords;
 
 					gt.board.off('up');
 
@@ -252,13 +252,13 @@
 				};
 
 				this.phase2 = (coords) => {
-					// Don't allow the second point to be created on the same
-					// vertical line as the first point or off the board.
+					// If the current coordinates are on the same vertical line as the first point or off the board,
+					// then use the coordinates of the highlight point instead.
 					if (
-						Math.abs(this.shiftPoint.X() - gt.snapRound(coords[1], gt.snapSizeX)) < JXG.Math.eps ||
-						!gt.boardHasPoint(coords[1], coords[2])
+						!gt.boardHasPoint(coords[1], coords[2]) ||
+						Math.abs(this.shiftPoint.X() - gt.snapRound(coords[1], gt.snapSizeX)) < JXG.Math.eps
 					)
-						return;
+						coords = this.hlObjs.hl_point.coords.usrCoords;
 
 					gt.board.off('up');
 
@@ -291,13 +291,13 @@
 				};
 
 				this.phase3 = (coords) => {
-					// Don't allow the third point to be created on the same
-					// horizontal line as the first point, or off the board.
+					// If the current coordinates are on the same horizontal line as the first point or off the board,
+					// then use the highlight point coordinates instead.
 					if (
 						Math.abs(this.shiftPoint.Y() - gt.snapRound(coords[2], gt.snapSizeY)) < JXG.Math.eps ||
 						!gt.boardHasPoint(coords[1], coords[2])
 					)
-						return;
+						coords = this.hlObjs.hl_point.coords.usrCoords;
 
 					gt.board.off('up');
 
@@ -369,7 +369,7 @@
 					this.hlObjs.hl_point.rendNode.focus();
 				}
 
-				// Make sure the highlight point is not moved off the board, that the sine wave is not degenerate.
+				// Make sure the highlight point is not moved off the board, and that the sine wave is not degenerate.
 				if (e instanceof Event) {
 					gt.graphObjectTypes.sineWave.adjustDragPosition(
 						e,
@@ -420,6 +420,7 @@
 
 				gt.setTextCoords(this.hlObjs.hl_point.X(), this.hlObjs.hl_point.Y());
 				gt.board.update();
+				return true;
 			},
 
 			deactivate(gt) {