[DONE] New expressions: "Object.GetXByAngleAndDistance(angle, distance)" and "Object.GetYByAngleAndDistance(angle, distance)"

[tristanbob]

Description

A gamedev knows a vector (angle and distance) and they want to know the endpoint position of the vector. This will be useful for any function that requires a position as input, such as position Tween and Pathfinding. This will make it easy to use tweens for knockback or dashes in any direction.

Solution suggested

Create two new expressions:

Object.VectorX(angle, distance) = Given an angle and distance, return the X position of the resulting vector.
Object.VectorY(angle, distance) = Given an angle and distance, return the Y position of the resulting vector.

This can be calculated using trigonometry functions:

Object.VectorX(angle, distance) = return Object.X() + (distance * cos(ToRad(angle)))
Object.VectorY(angle, distance) = return Object.Y() + (distance * sin(ToRad(angle)))

[4ian]

This would be surely interesting. Note that we have the reverse already:

• For objects:
  • get the angle: Object.AngleToObject, Object.AngleToPosition
  • get the distance: Object.Distance (should have been called DistanceToObject... no big deal), Object.DistanceToPosition (and the squared equivalent: SqDistance, SqDistanceToPosition).
• Expressions:
  • angle: AngleBetweenPositions
  • distance: DistanceBetweenPositions

Note that to be useful in most cases, the Angle and Distance for objects are from the object center.

So what you're suggesting is to offer the reverse operation.

I'm not sure about two things.

1. The naming. Basically, we translate from "polar coordinates" to "cartesian coordinates". In GDevelop, we don't talk about cartesian coordinates but just about "X/Y" and we don't tell usually "Polar" coordinates, but just "Distance and angle to somewhere/something". So should we should call this:

• VectorX/Y
• PolarVectorX/Y
• something else? DistanceAndLengthX/Y?

2. The Object.VectorX/Y should be, to be consistent with what's existing, calculated from the object center.

[tristanbob]

1. The Object.VectorX/Y should be, to be consistent with what's existing, calculated from the object center.

Do you mean this should use PointX("Center")? If so, it will restrict this function to only working with Sprites (which might be OK). I'm not sure how else we can calculate the center, since people can change the origin point.

[Silver-Streak]

If we're looking to keep the same naming structure, I'd think "PositionByAngleAndDistance", "Object.PositionByDistanceAndAngle" are both accurate but also relatively long.

[4ian]

Yes that would work even if a bit verbose PositionXByDistanceAndAngle/PositionYByDistanceAndAngle .
Could also by without abbreviation: XByDistanceAndAngle/YByDistanceAndAngle but maybe too implicit now..

[Triarite]

I can personally say that adding a Vector expression or whatever you prefer to call it would prove extremely useful to my projects. I, of course, can't speak for others. But it doesn't seem like this would be such a difficult expression to add, and considering how helpful it could prove to be I'm not sure why it can't be added, and sooner rather than later at that.

[Silver-Streak]

@4ian Just chiming back in on this as it's come up again on the discord.

I think X/YByDistanceAndAngle, or maybe GetX/YByDistanceAndAngle works slightly better and is shorter than Position, but less implicit than x/y?

[tristanbob]

I prefer listing the angle first since that is what seems most natural: "If I head in this direction for 100 units, where will I end up?"

GetXByAngleAndDistance()
GetYByAngleAndDistance()

[4ian]

Usually expressions in GDevelop don't have Get prefix, because everything is a Get.

So would rather be:
XByAngleAndDistance(angle, distance)
YByAngleAndDistance(angle, distance)

The angle is indeed first in the action to set a force, so we'll probably keep this order here to.
I think I'm fine with this.

Last question, is it better to have XByAngleAndDistance or XFromAngleAndDistance? The "by" must be conveying better the idea of computing a new position from an angle and a distance (but in this sentence, I used "from").

[Silver-Streak]

Looking through http://wiki.compilgames.net/doku.php/gdevelop5/all-features/expressions-reference, there are currently 0 expressions with "By", and many expressions with "From", so From is more standard even if those expressions aren't position related, I suppose?

[Bouh]

I can add these new expressions XFromAngleAndDistance & YFromAngleAndDistance if you want, i just need to know:

• The text to show in the expression editor (Like: Angle between two objects)
• The long description (Like: Compute the angle between two objects. If you need the angle to an arbitrary position, use AngleToPosition.)

I can take care of the other points 👍

[4ian]

X position from angle and distance

Sounds good.

For the long description, I would even say: "Compute the X position when given an angle and distance relative to the starting object. This is also known as getting the cartesian coordinates of a 2D vector, using its polar coordinates."

So we have "vector" there for people that want the full explanation, and a reasonable name for the rest of users.

I would prefer to keep X/YFromAngleAndDistance because while we're talking about "vectors" here (i.e: a pair of coordinates), it's not obvious when you read 2DVectorX(180, 200) that the arguments are an angle and a length. On the contrary, in a traditional programming language, if I write 2DVector(180, 200), I would assume I'm creating a "2DVector" object with a x coordinate of 180 pixels and y coordinate of 200 pixels 😅
(and such a programming language could offer a static function like 2DVector.FromPolar(180, 200) or 2DVector.FromAngleAndDistance(180, 200), which we simplify in GDevelop to XFromAngleAndDistance(180, 200) as we don't deal with vector objects).

[Bouh]

Here the pull request with what the result is in preview
#2558

[4ian]

I have a sudden doubt about the naming. These expressions return the X and Y values from a starting point (the object center, or for the version without an object, the position 0;0) to a position that is specified by its angle and distance.
So we could name it: XToAngleAndDistance. But this looks like a conversion, while X is the result.
So we could name it too: AngleAndDistanceToX. But it sounds a bit weird.

So I think we can still keep XFromAngleAndDistance (X is the result, that's clear, and we get it from an angle and a distance).

Still writing this so you can all tell me if it makes sense.

[Bouh]

Your doubt create a doubt to me, if I add a free expression with XFromAngleAndDistance and an object expression with the same XFromAngleAndDistance it's ok or we have a potential problem of collision ?

[4ian]

Yes it's no problem, object expressions are scoped to objects.

[Bouh]

@tristanbob These expressions has been added in this pull request. You can try it in lastest nightly builds.

Expressions are:

//Object expressions
object.XFromAngleAndDistance(angle, distance)
object.YFromAngleAndDistance(angle, distance)

//Free expressions
XFromAngleAndDistance(angle, distance)
YFromAngleAndDistance(angle, distance)

This conversation can be marked solved :)