Filling out Signatures

Unreal Courses Talk
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1

Hello forum,

I’m curious about something that I noticed in this lecture. During the video, Ben uses the LineTraceSingleByChannel() method and in order to do so, he provides it with a hit result, a start location, an end location and a collision type.

However, in the Unreal documentation, this method calls for two additional lines, query parameters and response parameters.

I was under the impression that we had to complete every portion of the signature for these Unreal methods to operate correctly? In another video, we even created a “camera direction” variable that we didn’t even need just to complete a signature.

Any insight into this would be very much appreciated.

Cheers.

2

The last parameter has a default value

const FCollisionQueryParams& Params = FCollisionQueryParams::DefaultQueryParam

Parameters with default values aren’t needed unless you don’t want the default. And you can’t skip parameters, as in if there was something like

Something(int a, int b = 10, int c = 20);

and you want to keep b’s default but not c’s. You still need to go through the whole list to change c’s.

3

Hello Den

  1. why we can’t use crosshair position as a StartPosition for LineTraceSingleByChannel() instead of Camere position. Like this:

     int32 ViewportSizeX, ViewportSizeY; 
 GetViewportSize(ViewportSizeX, ViewportSizeY);

 FVector2D CrosshairPosiotn(ViewportSizeX / 2, ViewportSizeY / 3);
 FVector StartPosiotion(CrosshairPosition.X, CrosshairPostion.Y, 0); //  Did I create postion in the World or not?

 FVector LookDiretion;
 DeprojectScreenPositionToWorld( CrosshairPosition.X, CrosshairPosition.Y, Camera, LookDirection );

 FVector EndLocation = StartPosiotion + LookDiretion * 1000000;

 FHitResult HitResult;
 GetWorld()->LineTraceSingleByChannel( HitResult, StartPosition, EndLocation, 
        ECollisoinChannel::ECC_Visibility);

on other hand Camera position and AimPoint posiont is not same therefor aiming isn’t Properly

Crosshair_Camera
Crosshair_Camera1238×807 513 KB

4
  1. Because that’s the location on the 2d screen. It’s only going to have an X and Y, it wouldn’t be in the world.

Not sure what you mean by the other thing.

5

  1. Crosshair position is only Screen position and by this order:
    FVector StartPosiotion(CrosshairPosition.X, CrosshairPostion.Y, 0); I can’t convert it World location. did I correct understand?

  2. Ben takes Camera postion for StartLocation problem is that my Camera Location is higher than Crosshair positon therefor if I want to aim the Tank I have to lower down Crosshair, which is shown in the photo.
    I can change my camera position and equal it Crosshair postion but it also change viewpoint
    Is there anyway to start LineTrace from Crosshair position?

6

  1. With that, no. All you’re doing there is converting a FVector2D to a FVector.

    struct FVector2D
{
    FVector2D(float x, float y) { X = x; Y = y }
    float X;
    float Y;
}; 

struct FVector
{
    FVector(float x, float y, float z) { X = x; Y = y; Z = z; }
    float X;
    float Y;
    float Z;
}
int main()
{
    FVector2D CrosshairPosition(1.f,2.f);
    FVector Start(CrosshairPosition.X, CrosshairPosition.Y, 0.f);
}

    This is basically what you did… add a 0.

  2. Not sure why that would matter unless the object you are looking at is really close. They should both hit the same thing.

7

I think the problem is logical because Camera position is above to Crosshair outcome this aiming is not matching Crosshair. do you know how i can resolve this problem?
I know solution if I use GetHitResultAtScreenPosition() function but it significantly change my code and I want to follow the course

8

No I was wrong. My Aimpoint was attached wrongly. I solved the problem

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