Interrupt scrolling transitions in D3.js - d3.js

Question

I'm using the scrollama javascript library to write a "scrollytelling" article that involves transitioning D3 graphs in and out of view as the user scrolls. It is mostly working, but the graphs pile up on top of each other if I scroll too quickly.
Here is a jsfiddle based on this example by the scrollama author. In my example, the colored dots should fade in one at a time. If you were to scroll quickly to the end, the intermittent dots should not show up. The following snippets show how I've set up the transitions:
I define some functions that create my "graphs", and then call them.
var makeCircle0 = function(){
g.append("circle")
.attr("cx", 50)
.attr("cy", 100)
.attr("r", 20)
.attr("fill", "red")
.attr("class", "redcircle")
g.selectAll(".redcircle")
.attr("opacity", 0)
}
makeCircle0();
// Do this for makeCircle1, 2, and 3, also.
Then, I make functions to handle the transitions. This one says to make the red circle fade in and put the other circles at 0 opacity. I do this for all the circles/stages.
var showCircle0 = function(){
g.selectAll(".redcircle")
.transition()
.duration(1000)
.attr("opacity", 1)
g.selectAll(".yellowcircle").attr("opacity", 0)
g.selectAll(".greencircle").attr("opacity", 0)
g.selectAll(".bluecircle").attr("opacity", 0)
}
This section creates an array of my transition functions so that I can call them at specific steps in the page as you scroll. This is similar to how Jim Vallandingham handled his scroller.
var activateFunctions = [];
activateFunctions[0] = showCircle0;
activateFunctions[1] = showCircle1;
activateFunctions[2] = showCircle2;
activateFunctions[3] = showCircle3;
Finally, this calls the desired function at the right step in the page. Which it does... but not without halting the other transitions that got triggered in a previous step, resulting in multiple dots showing up at various stages.
function handleStepEnter(response) {
step.classed('is-active', function (d, i) {
return i === response.index;
})
figure.call(activateFunctions[response.index])
}
How can I prevent this?

Answer 1

If you need to interrupt a transition, d3-transition has a method for that:
selection.interrupt();
This will cancel a transition on an selection. If using named transitions you can specify a name by providing interrupt with one argument indicating the name of the transition to cancel.
If this is a generic version of your function to show an element:
function show() {
selectionToHide.attr("opacity",0);
selectionToShow.transition()
.attr("opacity",1);
}
Without using selection.interrupt you set the opacity to zero, and then the next tick of any transition in progress continues to update the opacity and finishes carrying out the transition. By adding interrupt we avoid that. Here's an updated fiddle.
However, there is another solution - we can apply another transition on the elements that we want to not show. To do so we just replace the transition with a new one:
function show() {
selectionToHide.transition()
.attr("opacity",0);
selectionToShow.transition()
.attr("opacity",1);
}
This will replace existing unnamed transitions (as yours are not named) and fade out elements, rather than simply hiding them all at once. Here's a fiddle of that. Of course if you have many elements this can be refined as to only apply a transition on any elements that are transitioning (not those that are already hidden) to reduce the amount of active transitions.
I haven't touched the scrolling, the circle that is shown should have its index match the displayed number, but it seems the number doesn't always match the scroll position, but this is a separate issue