How to find new sprite position from angle and speed?

Author

Message

Rich Dersheimer

AGK Developer

15

Years of Service

User Offline

Joined: 1st Jul 2009

Location: Inside the box

Posted: 2nd Jan 2018 22:47

Link

I'm maths challenged, and I need some kind soul to instruct me how to to have a sprite move across the screen according to its angle and speed. I know the sprite's current x, y, angle, and the distance I want it to travel.

Here's what I've tried...

+ Code Snippet


// virtual resolution
SetVirtualResolution (1024,768)

// some colors
colorWhite = MakeColor(255,255,255)
// make sprite
	DrawLine(0,0,30,10,colorWhite,colorWhite)
	Drawline(30,10,0,20,colorWhite,colorWhite)
	DrawLine(0,20,10,10,colorWhite,colorWhite)
	DrawLine(10,10,0,0,colorWhite,colorWhite)
	shipImg = GetImage(0,0,30,20)

spr=CreateSprite(shipImg)
SetSpritePosition (spr,512,768/2)
SetSpriteAngle(spr,0)

sprForce = 1.0

do
	sprAngle = GetSpriteAngle(spr)
	sprX = GetSpriteXByOffset(spr)
	sprY = GetSpriteYByOffset(spr)
	sprCosine = Cos(sprAngle) * sprForce
	sprSine = Sin(sprAngle) * sprForce
	sprX = sprX + sprCosine
	sprY = sprY + sprSine
	SetSpritePositionByOffset(spr,SprX,SprY)	

    print(sprAngle)
    sync()

loop
end

But when I try to change the angle as it moves, it doesn't do what I expect.

Any help would be appreciated!

Back to top

Profile PM Email

puzzler2018

User Banned

Posted: 2nd Jan 2018 22:54

Link

That code works perfect for me

Setting line

15... SetSpriteAngle(spr, 0) // goes right
15... SetSpriteAngle(spr, 90) // goes down
15... SetSpriteAngle(spr, 180) // goes left
15... SetSpriteAngle(spr, 270) // goes up

Or am i misunderstanding you

Back to top

Profile

Markus

Valued Member

20

Years of Service

User Offline

Joined: 10th Apr 2004

Location: Germany

Posted: 2nd Jan 2018 23:01 Edited at: 2nd Jan 2018 23:05

Link

i used

+ Code Snippet

		x = GetSpriteXByOffset(spr)
		y = GetSpriteYByOffset(spr)
		
		a = GetSpriteAngle(spr)
		
		a = a + curve[pos].turn * (180.0 / 60.0)
		
		x=x+sin(a) * curve[pos].speed
		y=y-cos(a) * curve[pos].speed
		
		SetSpriteAngle(spr,a)
		
		SetSpritePositionByOffset(spr,x,y)

in your case

+ Code Snippet

		x = GetSpriteXByOffset(spr)
		y = GetSpriteYByOffset(spr)
		
		a = GetSpriteAngle(spr)
				
		x=x+sin(a) * speed
		y=y-cos(a) * speed
		
		//SetSpriteAngle(spr,a)
		
		SetSpritePositionByOffset(spr,x,y)

https://en.wikipedia.org/wiki/Acceleration

AGK (Steam) V2017.12.12 : Windows 10 Pro 64 Bit : AMD (17.12.1) Radeon R7 265 : Mac mini OS High Sierra (10.13)

Back to top

Profile PM Email

Bengismo

7

Years of Service

User Offline

Joined: 20th Nov 2017

Location: Yorkshire, England

Posted: 2nd Jan 2018 23:02 Edited at: 2nd Jan 2018 23:06

Link

Its because you are using integers and needed to use floats (add # to position and even angle variables). If you use integers then the movement gets truncated and so it doesnt move right (it moves in jerks).

Your maths is sound....just the variables needed to change type. And if you do change an angle then save it back to the sprite too.

This code goes in a nice circle

+ Code Snippet

// virtual resolution
SetVirtualResolution (1024,768)
 
// some colors
colorWhite = MakeColor(255,255,255)
// make sprite
    DrawLine(0,0,30,10,colorWhite,colorWhite)
    Drawline(30,10,0,20,colorWhite,colorWhite)
    DrawLine(0,20,10,10,colorWhite,colorWhite)
    DrawLine(10,10,0,0,colorWhite,colorWhite)
    shipImg = GetImage(0,0,30,20)
 
spr=CreateSprite(shipImg)
SetSpritePosition (spr,512,768/2)
SetSpriteAngle(spr,0)
 
sprForce# = 1.0
 
do
    sprAngle# = GetSpriteAngle(spr)
	sprAngle# = sprAngle# +1
    sprX# = GetSpriteXByOffset(spr)
    sprY# = GetSpriteYByOffset(spr)
    sprCosine# = Cos(sprAngle#) * sprForce#
    sprSine# = Sin(sprAngle#) * sprForce#
    sprX# = sprX# + sprCosine#
    sprY# = sprY# + sprSine#
    SetSpritePositionByOffset(spr,SprX#,SprY#)    
	SetSpriteAngle(spr, sprAngle#)
 
    print(sprAngle#)
    sync()
 
loop
end

Back to top

Profile PM

Markus

Valued Member

20

Years of Service

User Offline

Joined: 10th Apr 2004

Location: Germany

Posted: 2nd Jan 2018 23:08 Edited at: 2nd Jan 2018 23:09

Link

Quote: "add # "

you can also use local blah as float
so u not need to enter # always.

at main.agc top you should use
#option_explicit

AGK (Steam) V2017.12.12 : Windows 10 Pro 64 Bit : AMD (17.12.1) Radeon R7 265 : Mac mini OS High Sierra (10.13)

Back to top

Profile PM Email

Bengismo

7

Years of Service

User Offline

Joined: 20th Nov 2017

Location: Yorkshire, England

Posted: 2nd Jan 2018 23:10

Link

The point was he needs to use floats - doesnt really matter how he does that as long as he does

Either way works

Back to top

Profile PM

puzzler2018

User Banned

Posted: 2nd Jan 2018 23:14

Link

Notice how the slightest thing can effect everything - like C++ missing that all important semi-colon, in this case the #, all good fun

Back to top

Profile

Markus

Valued Member

20

Years of Service

User Offline

Joined: 10th Apr 2004

Location: Germany

Posted: 2nd Jan 2018 23:16 Edited at: 2nd Jan 2018 23:19

Link

Quote: "The point was he needs to use floats"

yes me thought he declared it elsewhere.

and had a problem in sin/cos sign.

Quote: "Notice how the slightest thing can effect everything"

one char can break a app with thousands rows.

AGK (Steam) V2017.12.12 : Windows 10 Pro 64 Bit : AMD (17.12.1) Radeon R7 265 : Mac mini OS High Sierra (10.13)

Back to top

Profile PM Email

Rich Dersheimer

AGK Developer

15

Years of Service

User Offline

Joined: 1st Jul 2009

Location: Inside the box

Posted: 3rd Jan 2018 00:37

Link

Thanks guys, making all the appropriate variables into floats did the trick!

Back to top

Profile PM Email

Markus

Valued Member

20

Years of Service

User Offline

Joined: 10th Apr 2004

Location: Germany

Posted: 3rd Jan 2018 00:51

Link

use also the debugger and just copy this miraculous variables into for watching

AGK (Steam) V2017.12.12 : Windows 10 Pro 64 Bit : AMD (17.12.1) Radeon R7 265 : Mac mini OS High Sierra (10.13)

Back to top

Profile PM Email

Captain Ouais

20

Years of Service

User Offline

Joined: 12th Dec 2003

Location: France

Posted: 3rd Jan 2018 21:04

Link

Hello !
here's a function that moves a sprite forward by its angle, if that's what you need :

+ Code Snippet

function Move(sprite,speed as float)

SetSpritePositionByOffset (Sprite,GetSpriteXByOffset(sprite)+Sin(GetSpriteAngle(sprite))*speed,GetSpriteYByOffset(sprite)-Cos(GetSpriteAngle(sprite))*speed)

endfunction

I do what i do !!!

Back to top

Profile PM

Rich Dersheimer

AGK Developer

15

Years of Service

User Offline

Joined: 1st Jul 2009

Location: Inside the box

Posted: 5th Jan 2018 19:41

Link

That's very nice Captain, thanks!

Back to top

Profile PM Email

Sorry your browser is not supported!

AppGameKit Classic Chat / How to find new sprite position from angle and speed?