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‫Hello and welcome.

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‫In this lecture, we're going to be setting up our first geometry trace so that when we go and look

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‫at our gargoyle and we get close enough within range, then sure enough it prints out the name of the

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‫actor that has been hit by the trace.

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‫Let's dive in and see how we can do this so we're finally ready to tackle this sweep single by channel.

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‫There was a lot of pieces that we had to have in place to make it work.

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‫But finally, we're here.

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‫So let's have a look at the syntax of this function.

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‫So we are in a much better place to understand what was going on here when in these types.

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‫So the return value is a boolean, which basically tells us whether or not we found anything with the

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‫sweep.

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‫Now the second argument, as you can see here, it's a reference.

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‫It's got this ampersand.

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‫And it doesn't matter whether there's a space after the ampersand or a space between the variable name,

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‫it's all the same as long as there's an ampersand after the type saying that that type is a reference

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‫and it's a type called an F hit result, you can see that it's a struct.

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‫So this F hit result is the out hit.

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‫That is the result that comes out of the sweep.

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‫We can see what things have been hit and there's it's a struct because there's multiple different things,

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‫pieces of information that can come out of this sweep.

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‫Then we have a constant f vector reference.

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‫So this is taking our start vector by reference instead of copying it.

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‫Same with the end vector, then we've got a rotation.

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‫So this is the rotation of the shape using an f quat, which is an alternative structure to using the

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‫f rotator.

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‫We'll see how we can basically just get put in a zero rotation here because we're using a sphere.

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‫It doesn't really matter.

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‫The next thing that comes in is the Trace Channel and we'll see how to figure out what our Trace channel

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‫is called in C++.

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‫And then we've got our collision shape, which will be the last argument we need to provide, and we'll

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‫see how we can create a sphere of a certain radius by doing that.

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‫But before we begin, we'll need to know what that radius is and how have it configured.

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‫So we're going to go over into our grab a dot h, we're going to remove these functions we've been using

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‫as examples for reference references and out parameters.

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‫And we're going to create a new property which is going to be edit anywhere and it's going to be a float

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‫called the grab radius and we're going to set that to 101 metre.

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‫So let's go over into the C++ now and remove the references to print damage and has damage and we can

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‫remove any of that from the tick component as well.

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‫The whole if statement and where we're passing in the damage because here we're drawing our debug line

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‫and now we want to make a call to our sweep single by channel.

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‫So we're going to type sweep.

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‫So we're going to type get world parentheses because we know that this is a function on the new world

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‫object.

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‫Then we can do an arrow because we know that get world returns a pointer and then we're going to do

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‫a sweep single by channel like so and we're going to have to input an out parameter for it to populate

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‫as the first argument here.

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‫So we're going to create a variable that's going to be empty, that will be populated, and it's got

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‫to have the right type.

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‫So it's going to be an if f hit result and we're just going to call the variable itself hit result,

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‫put a semicolon at the end because we're not initializing it, we're not giving it any value, but we're

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‫going to pass it in for it to be given a value by the sweep single by channel function.

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‫So that's our hit result.

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‫Then we need to pass in the start and end vectors which we know are going to be not copied but taken

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‫a reference to.

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‫Now we need to populate the rotation which we can do with a simple f quote colon, colon identity,

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‫which tells us basically that this is a no rotation.

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‫That's just a bit of a weird language for it.

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‫It's a mathematical speak for meaning that this is no rotation.

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‫Next up, we need the trace collision channel.

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‫Now, how do we go about finding that trace collision channel?

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‫Well, if we go over to the folder that holds our project and we go in to config and then we go to the

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‫default engine INI right, click that and go open with Visual Studio code.

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‫And in here I'd like to search for Grabber.

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‫So you'll be able to see the collision response channel for the grabber.

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‫And it's basically been set up here in the default engine INI.

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‫It's only mentioned once in the whole file and you can see the channel name.

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‫This is the channel name in C++.

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‫It's not very.

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‫Yes, but it's s.e.c.

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‫Game Trace Channel two, so we can go ahead and copy that, and then we can go back to our grab a CP

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‫and paste it in here as the trace channel that we want.

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‫Now, this line is getting rather long, and what we can do to compensate for that is we can actually

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‫put each of these parameters on separate lines, or at least spread them out.

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‫So maybe the start and end are on the same.

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‫The identity criterion is on one line, the trace channel is on another line like so.

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‫And that just gives us a little bit more space for reading these long argument lists.

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‫Now, if we head back to the documentation, we can see that the next thing we need to pass in here

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‫is an F collision shape.

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‫So we need to construct a shape.

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‫Maybe we'll do this as a separate variable up at the top.

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‫I'll just do it before the F hit result to make it super clear that the F hit result is actually an

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‫out parameter.

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‫I'm always going to leave that as the last thing before the call to the function.

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‫So we're going to create an F collision shape, which we're going to call the sphere, and we're going

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‫to set it equal to F collision shape, colon, colon, make sphere.

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‫So that's going to create us a new sphere, collision shape.

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‫And the argument to this function is the sphere radius which we have got as the grab radius variable

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‫that we've configured as a U property but a semicolon on the end of this line and we can pass in the

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‫sphere as our final argument to the sweep channel function and put a semicolon at the end of that line.

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‫Now one more thing is that this function we know returns a boolean, which is whether we've hit anything.

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‫So I'm going to put the result into a boolean variable called has hit and that's what we're going to

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‫be using later on in this function.

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‫So I'd like to challenge you to print the hit actor's name.

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‫So now we've got this sweep happening.

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‫We should be able to get some results out of it.

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‫So use an if statement to print if we have anything at all.

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‫So if that boolean is true, that's when we're going to print out the actor name.

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‫You're going to get the actor that the Sphere Trace is hit by using the hit result struct.

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‫It's got a method on it which you can access with a dot operator because it's a struct in.

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‫It's not a pointer to the struct.

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‫You can do a dot, get actor and use the parentheses and that returns you an actor pointer.

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‫Then using that active pointer, you can get the actor's name using the get actor name or label method

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‫and think about whether you want to use the dot or arrow operator for this and then compile and test

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‫having printed out that actor name and see what you can hit in the scene.

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‫Pause the video and have a go.

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‫Okay.

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‫Welcome back.

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‫So we're going to start off with creating that if statement.

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‫So if has hit, then we're going to put some braces and we're going to do first of all, we want to

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‫get hold of that actor point.

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‫So a actor star hit actor is equal to the hit result.

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‫Dot get.

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‫Actor.

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‫Parentheses.

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‫Like.

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‫So then we're going to do a u log and we're going to write hit actor colon percent sx and we can do

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‫hit actor and because it's a pointer here, we can do hit actor arrow, get actor name or label, then

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‫some parentheses.

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‫And because this is a string, we have to put a star at the front of the whole shebang so that it can

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‫properly display it in our Yui log.

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‫Okay, so we now need to just go ahead and compile this.

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‫Then once we're in the scene, let's open up the output log and dock it to the layout so we can see

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‫it while we play and hit the play button.

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‫And instantly you can see that we are hitting that gargoyle statue.

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‫If I turn around and look at something else you can see, well, it's not very clear whether I'm not

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‫hitting anything or whether it's displaying nothing.

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‫So what I'm going to do is I'm going to put in an else to our if statement here, put some more brackets

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‫and I'm going to do another U log.

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‫And this time the text is going to say, no actor hit, let's recompile and go and play in the editor.

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‫And you can see it now.

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‫It's saying no actor hit all the time until I go and start looking at the gargoyle.

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‫And now it's saying that the gargoyle is the thing being hit.

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‫If I move too far back out of there for me to range, you can see I see that it's saying no actor being

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‫hit again.

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‫Great stuff.

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‫So we have now done a geometry sweep with a spherical object and we can see that it is indeed reacting

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‫only to the actors in our particular Trace channel, such as the Gargoyle is the only one that we set

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‫up at the moment.

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‫So that's the only one that it's finding.

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‫I'll see you in the next lecture.