frame an object - GameCreators Forum

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smerf

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Joined: 24th Feb 2005

Location: nm usa

Posted: 20th Nov 2019 08:37 Edited at: 20th Nov 2019 08:38

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I need some help with this been working on it to no avail.
i have an object of known size. for example 4 units. if i divide by 2 i get 2 units aka my radius.
using screenx=getscreenxfrom3d(objposx#+radius,objposy#,objposz#) so plgging in the object current position plus its radius should give me the screen coord of its outside edge.

so then i want to frame the object with a circle
so i get the object centerpoint
x=getscreenxfrom3d(objposx#,objposy#,objposz#)
y=getscreenyfrom3d(objposx#,objposy#,objposz#)

now i want to draw a circles on x,y and scale the x and y radius to screenx.
but we need to take screenx and subtract x , "outside to center in screen coords" to determine how many pixels to draw

DrawEllipse(x,y,screenx-x ,MakeColor(128,128,255),MakeColor(128,128,255),0)

this code works for the most part but when the camera rotates on the z axis the size of the circle changes and is not consistent. any longer i dont know whats going on. aslo from one side it is large and viewing from the other side very small

+ Code Snippet

for i= 100 to 200
		x=GetScreenXFrom3D (star[i].posx,star[i].posy,star[i].posz)
		y=GetScreenyFrom3D (star[i].posx,star[i].posy,star[i].posz)
		
		
		`settextposition(i,x#,y#)
	next
	print("now in multiplayer")
	
	
	
	starx#=star[120].posx
	stary#=star[120].posy
	starz#=star[120].posz
	
	
	`screenx1=abs(getscreenxfrom3d(starx#-(star[120].size/2),stary#,starz#))
	screenx2=getscreenxfrom3d(starx#+(star[120].size/2),stary#,starz#)
	screenx=abs(getscreenxfrom3d(starx#,stary#,starz#))
	screeny=abs(getscreenyfrom3d(starx#,stary#,starz#))
	
	//DrawEllipse(screenx,screeny,(screenx2-screenx1)*,atan2(distance,getcameray(1)),MakeColor(128,128,255),MakeColor(128,128,255),1)
	if GetObjectInScreen(120)=1
		if screenx >screenx2
			temp1=screenx
			temp2=screenx2
	endif
	if screenx2 >screenx
		temp2=screenx
		temp1=screenx2	
			
	endif
		DrawEllipse(screenx,screeny,(temp1-temp2)*2,(temp1-temp2) *2,MakeColor(128,128,255),MakeColor(128,128,255),0)
	endif

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Bengismo

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Joined: 20th Nov 2017

Location: Yorkshire, England

Posted: 20th Nov 2019 11:13 Edited at: 20th Nov 2019 11:35

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This post has been marked by the post author as the answer.

You are measuring the screen position along just the x axis which is fine if your camera isnt rotated at all..but if it is rotated that 3d location could be almost directly behind or infront of the centre of the camera view meaning your circle will indeed be tiny depending on rotation. (at 90 degrees rotation about Y axis the circle will be tiny)

There's quite a few ways of fixing it ...i will list 2 for now....

1) Easy way: You could temporarily move the camera along its local x (MoveCameraLocalX,Y,Z()) by the radius of you object and get the change in camera x,y and z positions then move it back to where it was again. Then add those changes in values dx#, dy#, dz# to your objects position and take the screen x and y position from that. That will work and give you a consistant circle size that isnt dependant on camera rotations.

+ Code Snippet

	
	// Your Object radius
	radius# = 2.0
 
	// Get the objects centre on screen
	xs# = GetScreenXFrom3D(x#,y#,z#)
	ys# = GetScreenYFrom3D(x#,y#,z#)

	// get camera position
	ocx# = GetCameraX(1)
	ocy# = GetCameraY(1)
	ocz# = GetCameraZ(1)
	
	// move the camera and get the difference in values (Ie camera x vector)
	MoveCameraLocalX(1,radius#)
	cx# = GetCameraX(1) - ocx#
	cy# = GetCameraY(1) - ocy#
	cz# = GetCameraZ(1) - ocz#
	
	// Reset the cameras position
	SetCameraPosition(1,ocx#,ocy#,ocz#)
	
	// calculate the 2d circle radius
	rad# = GetScreenXFrom3D(x#+cx#,y#+cy#,z#+cz#) - xs#
	
	// Draw a circle with correct radius
	DrawEllipse(xs#,ys#,rad#,rad#,col,col,0)

2) Nerdy Ass Math based method: You can do some trigonometry/quaternion maths to impress the ladies with...

+ Code Snippet

	// Your Object radius
	radius# = 2.0
	
	// Get the objects centre on screen
	xs# = GetScreenXFrom3D(x#,y#,z#)
	ys# = GetScreenYFrom3D(x#,y#,z#)
	
	// Get the camera x vector	multiplied by the radius of your object
	cx# = radius# * (1 - 2 * (GetCameraQuatY(1)*GetCameraQuatY(1) + GetCameraQuatZ(1)*GetCameraQuatZ(1)))
	cy# = radius# * 2 * (GetCameraQuatX(1)*GetCameraQuatY(1) + GetCameraQuatW(1)*GetCameraQuatZ(1))
	cz# = radius# * 2 * (GetCameraQuatX(1)*GetCameraQuatZ(1) - GetCameraQuatW(1)*GetCameraQuatY(1))
	
	// calculate the 2d circle radius  (right edge minus the centre we retrieved above)
	rad# = GetScreenXFrom3D(x#+cx#,y#+cy#,z#+cz#) - xs#
	
	// Draw a circle with correct radius
	DrawEllipse(xs#,ys#,rad#,rad#,col,col,0)

Either of these works

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smerf

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Joined: 24th Feb 2005

Location: nm usa

Posted: 21st Nov 2019 00:50

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Ill always take a nerdy math option if available

. Thank you so much Bengismo it works perfectly. ive been diving into a massive amount of trigonometry lately. Never thought id need it for anything now having to learn it on the fly at every turn there is a new math problem. I am unfamiliar with Quaternary so ill have to do some research on those as well. I was unaware the cameras current angle and position would affect get 3d from and object.

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smerf

19

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Joined: 24th Feb 2005

Location: nm usa

Posted: 21st Nov 2019 06:15 Edited at: 21st Nov 2019 06:31

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Hey math wizard benjiso I have another problem. Ive been researching trig all day and have devised the following function to calculate the position of an object to the camera and return the camera angle relative tot he object but it is broken and i dont know how to make it work. I am def trying here.

+ Code Snippet

 
function distance2d(x1#,x2#,z1#,z2#,y1#,y2#)
	adjecent#=sqrt((x2#-x1#)*(x2#-x1#)   +(z2#-z1#)*(z2#-z1#)) //2d distance adjecent
	opposite#=abs(y2#-y1#) //height
	tempangle#=opposite#/ Adjecent#
	radiansangle#=(tan(tempangle#))
	`cameraangle1#=sin(radiansangle#)
	degrese#=sin(radiansangle# *180/3.1415926)
endfunction (degrese#*10000)
	
	

DO
        angletoobject#= distance2d(star[120].posx,GetCameraX(1),star[120].posz,getcameraz(1),star[120].posy,getcameray(1)) //returns straight line 2d distance
	print(str(angletoobject#)

sync()
loop

or should i use vector maths?

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