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‫Hello and welcome.

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‫In this lecture we are going to be drawing debug lines into our scene so that we can visualize what

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‫it is that a line trace is doing or what it should be doing, and figure out if our values that we're

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‫calculating are correct.

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‫Let's dive in and have a look.

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‫So as we can see, our sweep multi bi channel function requires a start and an end vector.

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‫Now it can be a little bit hard to figure out what's going on with these functions when we actually

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‫use them.

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‫Because if you start using it and you don't get back the results you're expecting, you can sometimes

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‫leave yourself wondering, Well, did I ask the right question in the first place?

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‫Did I send in the right start and end vectors even?

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‫Well, to figure that out, what we're going to do is use another function here called the draw debug

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‫line so that we can definitely see where the start and end vectors are, basically by drawing a line

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‫between them and given this is exactly the kind of thing that's going to be done by our sweep, then

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‫this is a good way of seeing, first of all, whether we've got the right inputs in in the first place.

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‫So you can see here that the draw debug line requires quite a few arguments, but not all of them are

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‫actually required.

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‫Only the first three, four or five.

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‫So we've got the first thing that comes in is a new world.

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‫We know how to get hold of the world.

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‫Now we've got then the line start, which is in a vector.

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‫We've got a line end again, which is a vector, then an F colour, which is something we haven't come

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‫across before, but you can click on it to find out what it is.

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‫And essentially it is a type like F vector that represents colours and there are a few handy colours

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‫already built in for us that allow us to just say, Hey, we want a black, we want blue, green, whatever.

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‫You can just use a colour name rather than having to specify the R, g b values.

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‫And then the final few through here are whether we've got the persistent lines, which tells us whether

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‫the line sticks around or whether it goes away at the end of the frame tells us the lifetime.

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‫So how many seconds does it stick around for the depth priority and the thickness, which neither of

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‫which we will be using?

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‫So the other useful piece of information on this documentation page is the include.

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‫So you can see here to use this function, we need to be using the header file that declares it, which

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‫is the hash include draw debug helpers.

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‫So let's go ahead and get that first of all, because that's going to make sure that autocomplete works

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‫in Visual Studio.

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‫If you don't have the header files, then Visual Studio doesn't actually know how to auto complete these

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‫functions.

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‫Then we're going to go down in to tick component and I am going to get rid of our log message for the

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‫get well get time.

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‫We'll get rid of all of this time, in fact.

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‫And you know what?

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‫We're just going to empty out our tick function, everything after our super colon, colon tick component

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‫we're going to remove and we're going to start with the draw debug line.

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‫So draw debug line and then open some parentheses.

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‫If you hit a control space, then you can see the parameters we were just talking about and some more

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‫information that wasn't available there, such as their default values.

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‫Some of them have default values, particularly after persistent lines.

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‫You can see the default value is false.

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‫So you don't actually have to provide an argument if it has a default value, but you can see that the

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‫colour doesn't have a default value.

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‫So we do need to provide everything up to that point.

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‫So the first thing is the world little mini challenge.

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‫How do you get hold of and pass in the world into draw debug line.

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‫You do a get world parentheses like so then we're going to need a start and an end.

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‫So for that I'm going to create two variables just before draw debug line and I'm not going to fill

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‫them out just yet.

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‫So if vector start and F vector end and those are going to be our next two parameter start and end,

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‫and then we need to give a color to do the color we can do F color, colon, colon, and then we can

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‫use one of those predefined colors such as red is always a good one.

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‫You can easily see it.

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‫And then in this case, because we're doing it in tick and we're doing every frame, we're writing this

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‫line to the screen, we can just use the persistent lines equals false.

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‫So every ticket will be redrawing this debug line, close the parentheses and then we can put the semicolon

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‫at the end of the line.

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‫So what are these start and end values going to look like?

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‫Well, at the start, it's literally just going to be the location of our grabber component because

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‫that's going to be attached to the camera and that is a good start location.

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‫Now remember that there is a forward vector for this component, for the camera, for the grabber,

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‫and that forward direction is going to be pointing out from the camera out into the scene, always pointing

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‫forward.

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‫So what we want to do is take our start vector, add the forward vector multiplied by some amount.

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‫Basically that's some amount is going to be the maximum distance that we are going to look for the object.

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‫So you might have one or two or three meters as the amount and then we're going to end up with an end

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‫vector.

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‫So the start plus the forward vector of the grabber is going to equal the end vector.

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‫So that maximum depth that we want to look into the scene is something that we might want to configure.

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‫So we'll put it as a you property on the grabber.

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‫Let's go over to the grabber door H and create a private section, make a U property that we're going

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‫to make edit anywhere and then we're going to have the type B of float so that it can be any numerical

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‫distance.

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‫And we're going to call this the max grab distance and we'll set it to a distance of four meters by

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‫default.

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‫Maybe that will have to be 400 because the default unit is centimeters.

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‫So I'd like to challenge you to calculate those starts and ends.

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‫Use the get component location in the first instance, use the get forward vector to calculate end and

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‫multiply by the max grab distance that we've just configured there.

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‫Then compile, play and eject from your actor because this line is going to be going straight down the

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‫camera.

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‫You may not see it initially.

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‫So eject.

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‫Come and step out of your own body and can you see the line pause, video and have a go.

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‫Okay.

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‫Welcome back.

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‫So let's go into the grab a EP and start writing what we're going to put in start.

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‫As we've said, there's simply just going to be the get component location and then the start.

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‫The end rather is going to be the start, plus the get forward vector multiplied by the max grab distance

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‫like so put a semicolon on the end of that line.

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‫We're going to go ahead and compile and if it compiles successfully, let's go ahead and hit play and

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‫then get our mass in the viewport hit f eight to eject out.

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‫And if we step out of ourselves, you can see the line clear as day coming from where our camera was

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‫all the way down into the floor.

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‫And probably if I come out, we may even be able to see that it's poking a little bit out of the bottom

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‫of the floor as well.

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‫That's four meters for you.

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‫So we've got a start, we've got an end.

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‫And if we were to use this line, this would be an excellent one for the input parameters to our geometry

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‫sweep that we're going to be using later on.

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‫Great stuff.

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‫We've learnt how to draw debug lines into our scene.

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‫This is a very useful skill that you'll use a lot when you can't understand why something is not working.

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‫I hope you enjoyed it.

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‫I'll see you in the next lecture.