One of the trickier questions facing the Mavs right now is how good is Harrison Barnes?

We know for sure he is good — almost 20 points per game on respectable shooting numbers is good, even if it’s on a losing team. There’s much fuss over Barnes’ ability to draw contact, get to the free throw line and score in ways that aren’t just mid-range jump shots, all of which are legitimate worries. There are plenty of ways he can get better.

The Mavs need to know how good Barnes is because they’re potentially going to build their whole team around him. If Barnes tops out at what he is now, that’s fine! Teams need guys who can get buckets, and Barnes can get buckets.

But if Barnes has already topped out, it’ll mean a ceiling for the Mavs’ roster planning going forward, unless they absolutely smash this upcoming first-round pick. That’s why what Barnes did Sunday against the Bucks was so mesmerizing. He looked like a number one option for the modern NBA.

He finished with 31 points on just 13 shots, made three three-pointers and had 10 free-throw attempts. His combined number of made threes and free throws (13) tied for the highest number he’s had this year. Barnes took over in the fourth quarter in a way he hasn’t all season, and he showed us a glimpse of what he could become if this off-season is as fruitful for him as the last.

The free throws are really what were eye-popping on Sunday. Barnes only averages 3.6 free-throw attempts, despite playing 37.3 minutes a night with a 25.5 percent usage rate. That’s bad. It’s OK for where Barnes is right now, learning to become a focal point for an offense, but if it doesn’t get better, it’ll handcuff him his whole career.

On Sunday, Barnes displayed an aggressiveness and quickness with the ball we haven’t seen a lot this year. Typically when Barnes gets the ball after getting a screen or setting a pick, he holds the ball and surveys his surroundings. It shows in the numbers — 49.3 percent of Barnes shot attempts come after he’s touched, or held, onto the ball between two and six seconds. That’s a big number for a non-creator like Barnes. For reference, dominant wing scorers like Paul George and Jimmy Butler’s percentage in that time frame (two to six seconds) is way less. Those guys take more shots after holding onto the ball for six seconds or more, but they’re also asked to create for others significantly more than Barnes is. If Barnes were creating more shots for his teammates, that number would be OK. He isn’t.

That’s why Sunday was such a refreshing change of pace. Instead of watching Barnes and seeing the gears turning in his head as he plots out his move, Barnes just received the ball and attacked. It’s a good thing for him, since he has a great first step. He routinely blows by wings and mismatched bigs when he’s assertive after the catch.

When Barnes has his mind made up to get to the rim before the catch, he gets there.

Both those drives ended in free throws, both started after attacking almost immediately after the catch.

The reason Barnes diversifying his game in this area is so crucial is because, honestly, he’s already got the hard part down. Efficient mid-range scoring is tough in the modern NBA, and while stars and MVP candidates like James Harden and Steph Curry basically only shoot from beyond the arc or at the rim, a mid-range game is crucial for clutch moments and playoff series where defenses are going to force you from the most efficient spots on the floor.

Teams form entire game plans to stop you from getting easy points in the playoffs. Creating in this area of the floor is crucial in creating offense when plays break down and defenses ramp up. If Barnes can give himself more easy points throughout a game, he’ll be a little fresher to get the hard ones when the game is on the line — and he’s already so good at those hard ones!

From there, more options will open up. If Barnes gets better at attacking the basket and creating contact, defenses will adjust. They’ll send more help when Barnes gets closer to the paint, and it’ll make his passing easier.

Luckily, he has three more seasons to get the knack of this and he’s only 24. Like I mentioned earlier, Barnes is pretty good! He can get buckets at an efficient-enough rate. But if the Mavs want to build around someone who is more than just pretty good, this is where Barnes has progress. Sunday was an exciting glimpse, a crack of the window into a future where Dallas has an offense that isn’t dependent on Dirk Nowitzki’s floor-spacing. It was nice.

We’ll see if Barnes keeps that window open.