How to target a sprite from another?

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Scraggle

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Joined: 10th Jul 2003

Location: Yorkshire

Posted: 29th Nov 2021 14:27 Edited at: 29th Nov 2021 15:15

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I'm trying to place an animated sprite between a gun with a turret and enemy sprites, rotating, scaling and positioning it so that it connects the two.
I've been playing with it all weekend but it isn't quite right.

I thought my maths was wrong but this morning I wrote some stand-alone code to isolate the issue and see if I could determine what was wrong but that works perfectly, so the issue is somewhere in my code and I just can't see it.
If any of you have any spare time, would you mind casting your eyes over the code and seeing if you can spot where I'm going wrong?

Here you can see that the targeting is slightly off:

And here is some stand-along code that work perfectly:

SetDisplayAspect(1)
SetWindowSize(800, 400, 0)
SetScissor(0, 0, 0, 0)
SetSyncRate(60, 0)

global gun, turret, tgt, laser

gun = CreateSprite(0)
SetSpriteSize(gun, 5, 5)
SetSpriteColor(gun, 0, 255, 0, 255)
SetSpritePositionByOffset(gun, 25, 50)

turret = CreateSprite(0)
SetSpriteSize(turret, 2, 2)
SetSpriteColor(turret, 255, 0, 0, 255)

tgt = CreateSprite(0)
SetSpriteSize(tgt, 5, 5)
SetSpriteColor(tgt, 0, 0, 255, 255)

laser = CreateSprite(0)
SetSpriteColor(laser, 0, 255, 255, 255)
SetSpriteOffset(laser, GetSpriteWidth(laser)*0.5, 0)

repeat
	MoveTarget(Timer() * 100)
	UpdateGun()
	ShowLaser(GetPointerState())
	
	sync()
until GetRawMouseRightPressed()

function MoveTarget(count)
	dist# = sin(count/3.0) * 50
	x# = 50 + sin(count) * dist#
	y# = 50 - cos(count) * dist#
	SetSpritePositionByOffset(tgt, x#, y#) 
endfunction

function UpdateGun()
	angle# = ATanFull(GetSpriteXByOffset(gun)-GetSpriteXByOffset(tgt), GetSpriteYByOffset(gun)-GetSpriteYByOffset(tgt))
	SetSpriteAngle(gun, angle#)
	SetSpriteAngle(turret, angle#)
	SetSpritePositionByOffset(turret, GetSpriteXByOffset(gun) + sin(angle#-180) * 5, GetSpriteYByOffset(gun) - cos(angle#-180) * 5)
endfunction

function ShowLaser(state)
	if state = 0
		SetSpriteVisible(laser, 0)
		exitfunction
	endif
	
	SetSpriteVisible(laser, 1)
	angle# = ATanFull(GetSpriteXByOffset(gun)-GetSpriteXByOffset(tgt), GetSpriteYByOffset(gun)-GetSpriteYByOffset(tgt))
	dist# = GetDistance(turret, tgt)
	SetSpriteAngle(laser, angle#)
	SetSpritePositionByOffset(laser, GetSpriteXByOffset(turret), GetSpriteYByOffset(turret))
	SetSpriteSize(laser, 0.5, dist#)
endfunction

function GetDistance(spr1, spr2)
	x# = GetSpriteXByOffset(spr1)-GetSpriteXByOffset(spr2)
	y# = GetSpriteYByOffset(spr1)-GetSpriteYByOffset(spr2)
	d# = sqrt(x#*x# + y#*y#)
endfunction d#

+ Code Snippet

SetDisplayAspect(1)
SetWindowSize(800, 400, 0)
SetScissor(0, 0, 0, 0)
SetSyncRate(60, 0)

global gun, turret, tgt, laser

gun = CreateSprite(0)
SetSpriteSize(gun, 5, 5)
SetSpriteColor(gun, 0, 255, 0, 255)
SetSpritePositionByOffset(gun, 25, 50)

turret = CreateSprite(0)
SetSpriteSize(turret, 2, 2)
SetSpriteColor(turret, 255, 0, 0, 255)

tgt = CreateSprite(0)
SetSpriteSize(tgt, 5, 5)
SetSpriteColor(tgt, 0, 0, 255, 255)

laser = CreateSprite(0)
SetSpriteColor(laser, 0, 255, 255, 255)
SetSpriteOffset(laser, GetSpriteWidth(laser)*0.5, 0)


repeat
	MoveTarget(Timer() * 100)
	UpdateGun()
	ShowLaser(GetPointerState())
	
	sync()
until GetRawMouseRightPressed()



function MoveTarget(count)
	dist# = sin(count/3.0) * 50
	x# = 50 + sin(count) * dist#
	y# = 50 - cos(count) * dist#
	SetSpritePositionByOffset(tgt, x#, y#) 
endfunction


function UpdateGun()
	angle# = ATanFull(GetSpriteXByOffset(gun)-GetSpriteXByOffset(tgt), GetSpriteYByOffset(gun)-GetSpriteYByOffset(tgt))
	SetSpriteAngle(gun, angle#)
	SetSpriteAngle(turret, angle#)
	SetSpritePositionByOffset(turret, GetSpriteXByOffset(gun) + sin(angle#-180) * 5, GetSpriteYByOffset(gun) - cos(angle#-180) * 5)
endfunction


function ShowLaser(state)
	if state = 0
		SetSpriteVisible(laser, 0)
		exitfunction
	endif
	
	SetSpriteVisible(laser, 1)
	angle# = ATanFull(GetSpriteXByOffset(gun)-GetSpriteXByOffset(tgt), GetSpriteYByOffset(gun)-GetSpriteYByOffset(tgt))
	dist# = GetDistance(turret, tgt)
	SetSpriteAngle(laser, angle#)
	SetSpritePositionByOffset(laser, GetSpriteXByOffset(turret), GetSpriteYByOffset(turret))
	SetSpriteSize(laser, 0.5, dist#)
endfunction


function GetDistance(spr1, spr2)
	x# = GetSpriteXByOffset(spr1)-GetSpriteXByOffset(spr2)
	y# = GetSpriteYByOffset(spr1)-GetSpriteYByOffset(spr2)
	d# = sqrt(x#*x# + y#*y#)
endfunction d#

And my in game code:
Bullet (lightning) creation:

+ Code Snippet

if time > tower[t].lastShootTime + tower[t].shootRate
		tower[t].lastShootTime = time
		tower[t].preshoot = FALSE
		
		b as tBullet
		b.damage = tower[t].damage
		b.tower = t
		b.target = tower[t].target
		b.born = time
		b.life = 0.5
		b.style = tower[t].bulletstyle
		b.spr = CreateSprite(bulletImage[b.style])
		SetSpriteDepth(b.spr, DEPTH_BULLETS)
		dist# = GetDistanceSqr(turretX#, turretY#, enemy[tower[t].target].pos.x, enemy[tower[t].target].pos.y)
		SetSpriteOffset(b.spr, GetSpriteWidth(b.spr)*0.5, 0)
		SetSpriteSize(b.spr, 0, 0)
		SetSpriteAnimation(b.spr, 53, 128, 6)
		PlaySprite(b.spr, 25, 1)

		b.ang = ang#
		bullet.insert(b)
	endif

Bullet Update:

+ Code Snippet

			case BULLET_LIGHTNING
				tgt = bullet[b].target
				twr = bullet[b].tower
				enemySpr = enemy[tower[twr].target].col
				ang# = GetSpriteAngle(tower[twr].spr[1])
				turretX# = tower[twr].pos.x + sin(ang#+180)*9.5
				turretY# = tower[twr].pos.y - cos(ang#+180)*9.5
				dist# = GetDistance(turretX#, turretY#, GetSpriteX(enemySpr), GetSpriteY(enemySpr))
				
				SetSpritePositionByOffset(bullet[b].spr, turretX#, turretY#)
				SetSpriteSize(bullet[b].spr, device.w * 0.025, dist#)
				SetSpriteAngle(bullet[b].spr, ang#)

				if time > bullet[b].born + bullet[b].life
					ChangeEnemyHealth(tgt, bullet[b].damage)
					tower[twr].target = -1
					KillBullet(b)
					continue
				endif
			endcase

I'm sure it's something obvious but I've been staring at it for so long now that I've gone code blind.
Any help would be much appreciated.

Thanks

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Scraggle

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21

Years of Service

User Offline

Joined: 10th Jul 2003

Location: Yorkshire

Posted: 29th Nov 2021 15:23 Edited at: 29th Nov 2021 15:25

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

Solved by Virtual Nomad
It was this line in the bullet update code:

+ Code Snippet

dist# = GetDistance(turretX#, turretY#, GetSpriteX(enemySpr), GetSpriteY(enemySpr))

That should have been get the sprites offset positions.
So very obvious but it had become invisible to me!

I'll leave this post here because the "stand-alone" contains some useful code for anyone doing something similar.

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PartTimeCoder

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Joined: 9th Mar 2015

Location: London UK

Posted: 3rd Dec 2021 05:09

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I late on this one but I did that exact same thing in my unfinished atom mash game

heres the function, it uses global type data but it can easily be edited to be generic, it will create the effect from startAtomID to endAtomID, or to the mouse if no endAtomID found, it scales the lightning effect to suit the distance and sets the correct angle, and yeah, I used offsets lol

Function GUI_Game_DrawMergeOverlay(mouse_x#, mouse_y#, startAtomID, endAtomID)
	
	if GetSpriteExists(startAtomID)
		
		// highlight the start sprite
		start_x#=GetSpriteXByOffset(startAtomID)
		start_y#=GetSpriteYByOffset(startAtomID)

SetSpritePositionByOffset(gGUIGame.spr_highlight_start, start_x#, start_y#)
		SetSpriteVisible(gGUIGame.spr_highlight_start, 1)

SetSpriteColor(gGUIGame.spr_highlight_start, 255, 255, 255, 175)
		SetSpriteColor(gGUIGame.spr_highlight_end, 255, 255, 255, 175)
		SetSpriteColor(gGUIGame.spr_highlight_line, 255, 255, 255, 175)

// check for an end sprite
		if GetSpriteExists(endAtomID)
			
			end_x#=GetSpriteXByOffset(endAtomID)
			end_y#=GetSpriteYByOffset(endAtomID)
			mid_x#=start_x#+(end_x#-start_x#)/2
			mid_y#=start_y#+(end_y#-start_y#)/2
			
			line_distance# = Distance2D(start_x#, start_y#, mid_x#, mid_y#)
			line_angle# = ATanFull(start_x#-mid_x#, start_y#-mid_y#)
			
			SetSpritePositionByOffset(gGUIGame.spr_highlight_line, start_x#, start_y#)
			SetSpriteAngle(gGUIGame.spr_highlight_line, line_angle#)
			SetSpriteSize(gGUIGame.spr_highlight_line, 32, line_distance#*2)
			SetSpriteVisible(gGUIGame.spr_highlight_line, 1)

SetSpritePositionByOffset(gGUIGame.spr_highlight_end, end_x#, end_y#)
			SetSpriteVisible(gGUIGame.spr_highlight_end, 1)
			
			Start_Atom_Type = GetSpriteGroup(startAtomID)
			End_Atom_Type = GetSpriteGroup(endAtomID)
			
			Select Collision_GetMergeStatus(Start_Atom_Type, End_Atom_Type)
				Case EVT_GOOD
					SetSpriteColor(gGUIGame.spr_highlight_start, 0, 255, 0, 175)
					SetSpriteColor(gGUIGame.spr_highlight_end, 0, 255, 0, 175)
					SetSpriteColor(gGUIGame.spr_highlight_line, 0, 255, 0, 175)
				EndCase
				Case EVT_UNKNOWN
					SetSpriteColor(gGUIGame.spr_highlight_start, 0, 0, 255, 175)
					SetSpriteColor(gGUIGame.spr_highlight_end, 0, 0, 255, 175)
					SetSpriteColor(gGUIGame.spr_highlight_line, 0, 0, 255, 175)
				EndCase
				Case EVT_BAD
					SetSpriteColor(gGUIGame.spr_highlight_start, 255, 0, 0, 175)
					SetSpriteColor(gGUIGame.spr_highlight_end, 255, 0, 0, 175)
					SetSpriteColor(gGUIGame.spr_highlight_line, 255, 0, 0, 175)
				EndCase
			EndSelect
	
		else
			// no end sprite, draw to the mouse
			mid_x#=mouse_x#+(start_x#-mouse_x#)/2
			mid_y#=mouse_y#+(start_y#-mouse_y#)/2	
			line_distance# = Distance2D(start_x#, start_y#, mid_x#, mid_y#)
			line_angle# = ATanFull(start_x#-mid_x#, start_y#-mid_y#)
			
			SetSpritePositionByOffset(gGUIGame.spr_highlight_line, start_x#, start_y#)
			SetSpriteAngle(gGUIGame.spr_highlight_line, line_angle#)
			SetSpriteSize(gGUIGame.spr_highlight_line, 32, line_distance#*2)
			SetSpriteVisible(gGUIGame.spr_highlight_line, 1)
			SetSpritePositionByOffset(gGUIGame.spr_highlight_end, mouse_x#, mouse_y#)
			
			SetSpriteVisible(gGUIGame.spr_highlight_start, 1)
			SetSpriteVisible(gGUIGame.spr_highlight_end, 0)
			SetSpriteVisible(gGUIGame.spr_highlight_line, 1)
			
			SetSpriteColor(gGUIGame.spr_highlight_start, 255, 255, 0, 175)
			SetSpriteColor(gGUIGame.spr_highlight_end, 255, 255, 0, 175)
			SetSpriteColor(gGUIGame.spr_highlight_line, 255, 255, 0, 175)
		endif
	else
		SetSpriteVisible(gGUIGame.spr_highlight_line, 0)
		SetSpriteVisible(gGUIGame.spr_highlight_end, 0)
		SetSpriteVisible(gGUIGame.spr_highlight_start, 0)	
	endif
	
EndFunction

+ Code Snippet

Function GUI_Game_DrawMergeOverlay(mouse_x#, mouse_y#, startAtomID, endAtomID)
	
	if GetSpriteExists(startAtomID)
		
		// highlight the start sprite
		start_x#=GetSpriteXByOffset(startAtomID)
		start_y#=GetSpriteYByOffset(startAtomID)

		SetSpritePositionByOffset(gGUIGame.spr_highlight_start, start_x#, start_y#)
		SetSpriteVisible(gGUIGame.spr_highlight_start, 1)

		SetSpriteColor(gGUIGame.spr_highlight_start, 255, 255, 255, 175)
		SetSpriteColor(gGUIGame.spr_highlight_end, 255, 255, 255, 175)
		SetSpriteColor(gGUIGame.spr_highlight_line, 255, 255, 255, 175)	
		

		// check for an end sprite
		if GetSpriteExists(endAtomID)
			
			end_x#=GetSpriteXByOffset(endAtomID)
			end_y#=GetSpriteYByOffset(endAtomID)
			mid_x#=start_x#+(end_x#-start_x#)/2
			mid_y#=start_y#+(end_y#-start_y#)/2
			
			line_distance# = Distance2D(start_x#, start_y#, mid_x#, mid_y#)
			line_angle# = ATanFull(start_x#-mid_x#, start_y#-mid_y#)
			
			SetSpritePositionByOffset(gGUIGame.spr_highlight_line, start_x#, start_y#)
			SetSpriteAngle(gGUIGame.spr_highlight_line, line_angle#)
			SetSpriteSize(gGUIGame.spr_highlight_line, 32, line_distance#*2)
			SetSpriteVisible(gGUIGame.spr_highlight_line, 1)

			SetSpritePositionByOffset(gGUIGame.spr_highlight_end, end_x#, end_y#)
			SetSpriteVisible(gGUIGame.spr_highlight_end, 1)
			
			Start_Atom_Type = GetSpriteGroup(startAtomID)
			End_Atom_Type = GetSpriteGroup(endAtomID)
			
			Select Collision_GetMergeStatus(Start_Atom_Type, End_Atom_Type)
				Case EVT_GOOD
					SetSpriteColor(gGUIGame.spr_highlight_start, 0, 255, 0, 175)
					SetSpriteColor(gGUIGame.spr_highlight_end, 0, 255, 0, 175)
					SetSpriteColor(gGUIGame.spr_highlight_line, 0, 255, 0, 175)
				EndCase
				Case EVT_UNKNOWN
					SetSpriteColor(gGUIGame.spr_highlight_start, 0, 0, 255, 175)
					SetSpriteColor(gGUIGame.spr_highlight_end, 0, 0, 255, 175)
					SetSpriteColor(gGUIGame.spr_highlight_line, 0, 0, 255, 175)
				EndCase
				Case EVT_BAD
					SetSpriteColor(gGUIGame.spr_highlight_start, 255, 0, 0, 175)
					SetSpriteColor(gGUIGame.spr_highlight_end, 255, 0, 0, 175)
					SetSpriteColor(gGUIGame.spr_highlight_line, 255, 0, 0, 175)
				EndCase
			EndSelect
	
		else
			// no end sprite, draw to the mouse
			mid_x#=mouse_x#+(start_x#-mouse_x#)/2
			mid_y#=mouse_y#+(start_y#-mouse_y#)/2	
			line_distance# = Distance2D(start_x#, start_y#, mid_x#, mid_y#)
			line_angle# = ATanFull(start_x#-mid_x#, start_y#-mid_y#)
			
			SetSpritePositionByOffset(gGUIGame.spr_highlight_line, start_x#, start_y#)
			SetSpriteAngle(gGUIGame.spr_highlight_line, line_angle#)
			SetSpriteSize(gGUIGame.spr_highlight_line, 32, line_distance#*2)
			SetSpriteVisible(gGUIGame.spr_highlight_line, 1)
			SetSpritePositionByOffset(gGUIGame.spr_highlight_end, mouse_x#, mouse_y#)
			
			SetSpriteVisible(gGUIGame.spr_highlight_start, 1)
			SetSpriteVisible(gGUIGame.spr_highlight_end, 0)
			SetSpriteVisible(gGUIGame.spr_highlight_line, 1)
			
			SetSpriteColor(gGUIGame.spr_highlight_start, 255, 255, 0, 175)
			SetSpriteColor(gGUIGame.spr_highlight_end, 255, 255, 0, 175)
			SetSpriteColor(gGUIGame.spr_highlight_line, 255, 255, 0, 175)
		endif
	else
		SetSpriteVisible(gGUIGame.spr_highlight_line, 0)
		SetSpriteVisible(gGUIGame.spr_highlight_end, 0)
		SetSpriteVisible(gGUIGame.spr_highlight_start, 0)	
	endif
	
EndFunction

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