Rotating Sprite Around A Point Without Messing Its Drawing Point

lifesuxtr · 2019-11-26T18:48:21

UPDATE: I solved my problem guys trick was to use powerIndicator.setOrigin(powerIndicator.width/2,0f) THANKS EVERYONE I am trying to draw and rotate an arrow sprite based on a point,around a static circle body without messing its drawing starting point. Arrow should be directed to the same direction with user touch point,static body center vector. Let me explain it with an example. This is how i calculate arrow drawing point: fun powerIndicatorDownPointCalculator(playerPosition: Vector2,touchPosition: Vector2,distanceBetweenTouchPointAndPlayer:Float):Vector2{ // player position is static body center,touch position is touch point. val playerPositionHolder = playerPosition.cpy() val abVector = playerPosition.sub(touchPosition); val normalizedAbVector = Vector2(abVector.x/distanceBetweenFingerAndPlayer,abVector.y/distanceBetweenFingerAndPlayer) Gdx.app.log("normalized ab vector",normalizedAbVector.toString()) var pointToAddX = 90*normalizedAbVector.x var pointToAddY = 90*normalizedAbVector.y var newPointX = playerPositionHolder.x + pointToAddX var newPointY = playerPositionHolder.y + pointToAddY Gdx.app.log("NEW POINT", Vector2(newPointX,newPointY).toString()) return Vector2(newPointX,newPointY) } Here is a simple video showing it: This is how i calculate C point to use later on rotation(?) fun calculateAimingPoint(playerPosition: Vector2,touchPosition: Vector2):Vector2{ //playerPosition is staticbody centerval abVector = playerPosition.sub(touchPosition); val secondPos = blackBody.position.cpy() val cPointPosition = secondPos.add(abVector) return cPointPosition } This is what i wrote for rotation but for sure it is wrong since not working as i wanted: var angle = atan2(aimingPoint.y - blackBody.position.y, aimingPoint.x - blackBody.position.x ) *180/ PI ; //aiming point is C point, blackBody is static body if (angle > 90) { angle = 450 - angle; } else { angle = 90 - angle; } // powerIndicator.setOrigin(????) // setOrigin is for rotation but i dont now what to write here. angle = angle*-1 powerIndicator.rotation = angle.toFloat() What i actually wanna achieve is this: As zakwayda suggested first i am trying to solve rotation problem. I fixed arrows position to central bodies center and trying to rotate to face with aim point. I have decided to work on rotation first.I fixed position of arrow to center of circular body and i am trying to face arrow towards aiming point. (shooter is central body) var xDownPoint = shooter.body.position.x-powerIndicator.width/2 var yDownPoint = shooter.body.position.y powerIndicator.setPosition(xDownPoint,yDownPoint) var degrees = (Math.atan2((aimingPoint.x - xDownPoint).toDouble(), -(aimingPoint.y - yDownPoint).toDouble()) * 180.0 / Math.PI - 180.0f).toFloat() powerIndicator.setOrigin(xDownPoint,yDownPoint) powerIndicator.rotation = degrees This is the result: https://im4.ezgif.com/tmp/ezgif-4-21ee1394147e.gif As you see starting position of arrow is messed up but i guess its rotation degree is correct

Math and Physics Programming

Started by lifesuxtr November 19, 2019 01:34 AM

11 comments, last by lifesuxtr 5 years, 2 months ago

bzt

November 21, 2019 02:31 PM

19 hours ago, JohnnyCode said:
why do you compete a single 3x2 matrix multiplication of a 2d vector with normalization and funcy stuff OP does?

Uhm, excuse me, but what? I was talking about vector multiplication by a scalar value. The OP's question was: provided T,P,A known, how to get C? I answered that question and gave a few pointers on how to rotate a bitmap arrow. Neither of those require matrix operations. That was all. I've answered how I would do it with the given configuration, now the rest is up to the OP.

Cheers,
bzt

lifesuxtr

Author

108

November 26, 2019 06:48 PM

@Zakwayda

You are right. I have decided to work on rotation first.I fixed position of arrow to center of circular body and i am trying to face arrow towards aiming point.

(shooter is central body)

var xDownPoint = shooter.body.position.x-powerIndicator.width/2  
var yDownPoint = shooter.body.position.y  
powerIndicator.setPosition(xDownPoint,yDownPoint)  
var degrees = (Math.atan2((aimingPoint.x - xDownPoint).toDouble(), -(aimingPoint.y - yDownPoint).toDouble()) * 180.0 / Math.PI - 180.0f).toFloat()     powerIndicator.setOrigin(xDownPoint,yDownPoint) 
powerIndicator.rotation = degrees

This is the result:

https://im4.ezgif.com/tmp/ezgif-4-21ee1394147e.gif

As you see starting position of arrow is messed up but i guess rotated correctly.

Rotating Sprite Around A Point Without Messing Its Drawing Point

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