How to implement parabolic path for projectiles

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JORGEMAL

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Posted: 24th May 2013 19:02

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I wonder if this question can be asked here.

I am planning to write a game in which there will be linear and parabolic shooting of projectiles. Linear shootings will have a slope, meaning that they will not necessarily be horizontal. I have thought about using linear and quadratic functions but I see that I would need to "save" every function while they are still being drawn on the screen. I guess this is not a good choice because a user can shoot too many times which implies to "save" too many functions.

I will very much appreciate any comment.

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george++

AGK Tool Maker

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Posted: 24th May 2013 19:22

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Actually your shootings should to be affected by some kind of gravity. Is it a side action game? If this is your case then the physics laws is your friend

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Markus

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Posted: 24th May 2013 22:37

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you have only to directions of forces.
the one is your shot and the other is your gravity.
looks like this:

shot to right
dx1=0.01
dy1=0.00

falling down
dx2=0.000
dy2=0.001

x=x+dx1+dx2
y=y+dy1+dy2

dependent on the frame timestep
if you want move 1 unit in 60 frames=1 second
it is speed*(1.0/60.0)

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easter bunny

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Playing: Dota 2

Posted: 25th May 2013 02:04

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You might be able to do it like this:

+ Code Snippet

#constant grav 0.02
type projectile
 id `Sprite id for object
 x as float `current x/y coors
 y as float
 xs as float `currect x/y SPEED for object
 ys as float
endtype

obj as projectile

obj.id = Createsprite(0)
SetSpriteSize(obj.id,10,10)
obj.x=20
obj.y=50
obj.xs=2
obj.ys=-2
SetSpritePosition(obj.id,obj.x,obj.y)
SetSpriteSize(obj.id,10,10)

do
 obj=updateproj(obj)
 sync()
 if GetPointerPressed() then end
loop

function updateproj(o as projectile)
  o.ys=o.ys+grav
 o.x=o.x+o.xs
 o.y=o.y+o.ys
SetSpritePosition(o.id,o.x,o.y)
endfunction o

[untested, might not work out-of-the-box]

Dodge those Balls, awesomest app on the Play Store

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Phaelax

DBPro Master

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Joined: 16th Apr 2003

Location: Metropia

Posted: 25th May 2013 04:47 Edited at: 25th May 2013 06:27

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Well the basic formula for a parabola is: ax^2 + bx + c

And then you have this:
x = v*cos(a)*t
y = v*sin(a)*t - ½gt²

The beauty with using time (t) in the equation is that it makes it easy to determine where your object is at any given moment. You just have to solve for T.
The equations are in my DB particle tutorial.

Demo

setVirtualResolution(640,480)

obj = createSprite(0)
setSpriteSize(obj, 16, 16)

setSpritePosition(obj, 500, y)

g# = 3.0
v# = 30
angle# = 45
t# = 0.0

baseX = 100
baseY = 300

DO

angle# = 270-atanful(baseX-getrawmousex(), getrawmousey()-baseY)

if getrawmouserightpressed() then v# = v# + 2
    if getrawmouseleftpressed() then v# = v# - 2

a_cos# = cos(angle#)
    a_sin# = sin(angle#)

// Show initial angle of projectile
    drawLine(baseX, baseY, baseX+a_cos#*100, baseY-a_sin#*100,0,255,0)

// Calculate at what time projectile will
    // fall back to ground level
    // y = v*sin(a)*t - ½gt²

// Draw points along projectile's path
    for i = 0 to 20
        t# = i
        x  = baseX + v#*a_cos#*t#
        y  = baseY - (v#*a_sin#*t# - 0.5*g#*t#^2)
        drawLine(x, y, x, y, 255,0,0)
    next i

// Ground level
    drawLine(0, baseY, 640, baseY,255,255,255)

t1# = t1# + 0.1
    x  = baseX + v#*a_cos#*t1#
    y  = baseY - (v#*a_sin#*t1# - 0.5*g#*t1#^2)
    setSpritePosition(obj, x, y)

if t1# > 20 then t1# = 0

print("Velocity: "+str(v#))
    print("Angle: "+str(angle#))

sync()
LOOP

+ Code Snippet


setVirtualResolution(640,480)

obj = createSprite(0)
setSpriteSize(obj, 16, 16)

setSpritePosition(obj, 500, y)



g# = 3.0
v# = 30
angle# = 45
t# = 0.0

baseX = 100
baseY = 300

DO



    angle# = 270-atanful(baseX-getrawmousex(), getrawmousey()-baseY)


    if getrawmouserightpressed() then v# = v# + 2
    if getrawmouseleftpressed() then v# = v# - 2

    a_cos# = cos(angle#)
    a_sin# = sin(angle#)


    // Show initial angle of projectile
    drawLine(baseX, baseY, baseX+a_cos#*100, baseY-a_sin#*100,0,255,0)


    // Calculate at what time projectile will
    // fall back to ground level
    // y = v*sin(a)*t - ½gt²


    // Draw points along projectile's path
    for i = 0 to 20
        t# = i
        x  = baseX + v#*a_cos#*t#
        y  = baseY - (v#*a_sin#*t# - 0.5*g#*t#^2)
        drawLine(x, y, x, y, 255,0,0)
    next i

    // Ground level
    drawLine(0, baseY, 640, baseY,255,255,255)


    t1# = t1# + 0.1
    x  = baseX + v#*a_cos#*t1#
    y  = baseY - (v#*a_sin#*t1# - 0.5*g#*t1#^2)
    setSpritePosition(obj, x, y)

    if t1# > 20 then t1# = 0

    print("Velocity: "+str(v#))
    print("Angle: "+str(angle#))

    sync()
LOOP

"You're all wrong. You're all idiots." ~Fluffy Rabbit

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