Need help establishing Physics forces always directly *behind* an object - propulsion system.

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ProfVersaggi

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Location: Maastricht Netherlands / Chicago, USA

Posted: 28th Feb 2013 23:39

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I'm attempting to construct a propulsion system for a physics sprite which will do nothing other than provide a force to push the object from the back to the front - think ship engines.

What it should not do is articulate 'direction', that function is handled elsewhere.

My problem is that the SetSpritePhysicsForce and SetSpritePhysicsImpulse functions 'both' have vx and vy parameters which dictate that the force itself pushes up/down/left/right depending on the positive/negative/zero values and the magnitude is determined by the size of the numbers (vectors). Unfortunately for me, it sets direction.

All I want is the push, not the direction...

Has anyone worked this out elsewhere?

I've done this before when manually articulating the directional values but it's really spit and duct tap ... and I can't do that at this stage.

` **** EngageShipPropulsion()
Function EngageShipPropulsion(angle#)

// Establish Ship heading angle ranges, corresponding propulsion force directions (Forward and reverse)

if angle# < -70 and angle# > -135           ` Up
                     ship.vx = ZERO
                     ship.vy = -ship.throttle#
                     ship.rvx = ZERO
                     ship.rvy = ship.throttle#
                     screen.viewOffsetIncrementX# = 0
                     screen.viewOffsetIncrementY# = -0.5
                     ship.heading$ = d_UP

elseif angle# > 70 and angle# < 130        ` Down
                     ship.vx = ZERO
                     ship.vy = ship.throttle#
                     ship.rvx = ZERO
                     ship.rvy = -ship.throttle#
                     screen.viewOffsetIncrementX# = 0
                     screen.viewOffsetIncrementY# = 0.5
                     ship.heading$ = d_DOWN

elseif angle# > 150 and angle# > -150       ` Left
                     ship.vx = -ship.throttle#
                     ship.vy = ZERO
                     ship.rvx = ship.throttle#
                     ship.rvy = ZERO
                     screen.viewOffsetIncrementX# = -0.5
                     screen.viewOffsetIncrementY# = 0
                     ship.heading$ = d_LEFT

elseif angle# > -45 and angle# < 45         ` Right
                     ship.vx = ship.throttle#
                     ship.vy = ZERO
                     ship.rvx = -ship.throttle#
                     ship.rvy = ZERO
                     screen.viewOffsetIncrementX# = 0.5
                     screen.viewOffsetIncrementY# = 0
                     ship.heading$ = d_RIGHT

elseif angle# <= -45 and angle# >= -70      ` Top-Right
                     ship.vx =  ship.throttle#
                     ship.vy = -ship.throttle#
                     ship.rvx = -ship.throttle#
                     ship.rvy = ship.throttle#
                     screen.viewOffsetIncrementX# = 0.5
                     screen.viewOffsetIncrementY# = -0.5
                     ship.heading$ = d_TOP_RIGHT

elseif angle# <= -130 and angle# >= -180    ` Top-Left
                     ship.vx = -ship.throttle#
                     ship.vy = -ship.throttle#
                     ship.rvx = ship.throttle#
                     ship.rvy = ship.throttle#
                     screen.viewOffsetIncrementX# = -0.5
                     screen.viewOffsetIncrementY# = -0.5
                     ship.heading$ = d_TOP_LEFT

elseif angle# <= 90 and angle# >= 45        ` Bottom-Right
                     ship.vx =  ship.throttle#
                     ship.vy =  ship.throttle#
                     ship.rvx = -ship.throttle#
                     ship.rvy = -ship.throttle#
                     screen.viewOffsetIncrementX# = 0.5
                     screen.viewOffsetIncrementY# = 0.5
                     ship.heading$ = d_BOTTOM_RIGHT

elseif angle# <= 180 and angle# >= 90       ` Botom-Left
                     ship.vx =  -ship.throttle#
                     ship.vy =  ship.throttle#
                     ship.rvx = ship.throttle#
                     ship.rvy = -ship.throttle#
                     screen.viewOffsetIncrementX# = -0.5
                     screen.viewOffsetIncrementY# = 0.5
                     ship.heading$ = d_BOTTOM_LEFT

endif
                ` **** Create the Physics Force to move the ship - place force directly behind back of the ship ******************************************
                CheckCurrentShipState()
                x# = -(ship.width#/2.0)*(Cos(angle#))+ship.absCtrX#                       ` Start from the absolute center of the ship,
                y# = -(ship.width#/2.0)*(Sin(angle#))+ship.absCtrY#                       ` go straight back 1/2 width & 1/2 height to place force pt.
                if (ship.reverseEngines = FALSE)                                          ` Engines Forward
                    SetSpritePhysicsImpulse(ship.sprID, x#, y#, ship.vx, ship.vy)
                elseif (ship.reverseEngines = TRUE)                                       ` Engines Reverse
                    SetSpritePhysicsImpulse(ship.sprID, x#, y#, ship.rvx, ship.rvy)
                endif
EndFunction

+ Code Snippet

` **** EngageShipPropulsion()
Function EngageShipPropulsion(angle#)

                // Establish Ship heading angle ranges, corresponding propulsion force directions (Forward and reverse)

                if angle# < -70 and angle# > -135           ` Up
                     ship.vx = ZERO
                     ship.vy = -ship.throttle#
                     ship.rvx = ZERO
                     ship.rvy = ship.throttle#
                     screen.viewOffsetIncrementX# = 0
                     screen.viewOffsetIncrementY# = -0.5
                     ship.heading$ = d_UP

                elseif angle# > 70 and angle# < 130        ` Down
                     ship.vx = ZERO
                     ship.vy = ship.throttle#
                     ship.rvx = ZERO
                     ship.rvy = -ship.throttle#
                     screen.viewOffsetIncrementX# = 0
                     screen.viewOffsetIncrementY# = 0.5
                     ship.heading$ = d_DOWN

                elseif angle# > 150 and angle# > -150       ` Left
                     ship.vx = -ship.throttle#
                     ship.vy = ZERO
                     ship.rvx = ship.throttle#
                     ship.rvy = ZERO
                     screen.viewOffsetIncrementX# = -0.5
                     screen.viewOffsetIncrementY# = 0
                     ship.heading$ = d_LEFT

                elseif angle# > -45 and angle# < 45         ` Right
                     ship.vx = ship.throttle#
                     ship.vy = ZERO
                     ship.rvx = -ship.throttle#
                     ship.rvy = ZERO
                     screen.viewOffsetIncrementX# = 0.5
                     screen.viewOffsetIncrementY# = 0
                     ship.heading$ = d_RIGHT

                elseif angle# <= -45 and angle# >= -70      ` Top-Right
                     ship.vx =  ship.throttle#
                     ship.vy = -ship.throttle#
                     ship.rvx = -ship.throttle#
                     ship.rvy = ship.throttle#
                     screen.viewOffsetIncrementX# = 0.5
                     screen.viewOffsetIncrementY# = -0.5
                     ship.heading$ = d_TOP_RIGHT

                elseif angle# <= -130 and angle# >= -180    ` Top-Left
                     ship.vx = -ship.throttle#
                     ship.vy = -ship.throttle#
                     ship.rvx = ship.throttle#
                     ship.rvy = ship.throttle#
                     screen.viewOffsetIncrementX# = -0.5
                     screen.viewOffsetIncrementY# = -0.5
                     ship.heading$ = d_TOP_LEFT

                elseif angle# <= 90 and angle# >= 45        ` Bottom-Right
                     ship.vx =  ship.throttle#
                     ship.vy =  ship.throttle#
                     ship.rvx = -ship.throttle#
                     ship.rvy = -ship.throttle#
                     screen.viewOffsetIncrementX# = 0.5
                     screen.viewOffsetIncrementY# = 0.5
                     ship.heading$ = d_BOTTOM_RIGHT

                elseif angle# <= 180 and angle# >= 90       ` Botom-Left
                     ship.vx =  -ship.throttle#
                     ship.vy =  ship.throttle#
                     ship.rvx = ship.throttle#
                     ship.rvy = -ship.throttle#
                     screen.viewOffsetIncrementX# = -0.5
                     screen.viewOffsetIncrementY# = 0.5
                     ship.heading$ = d_BOTTOM_LEFT

                endif
                ` **** Create the Physics Force to move the ship - place force directly behind back of the ship ******************************************
                CheckCurrentShipState()
                x# = -(ship.width#/2.0)*(Cos(angle#))+ship.absCtrX#                       ` Start from the absolute center of the ship,
                y# = -(ship.width#/2.0)*(Sin(angle#))+ship.absCtrY#                       ` go straight back 1/2 width & 1/2 height to place force pt.
                if (ship.reverseEngines = FALSE)                                          ` Engines Forward
                    SetSpritePhysicsImpulse(ship.sprID, x#, y#, ship.vx, ship.vy)
                elseif (ship.reverseEngines = TRUE)                                       ` Engines Reverse
                    SetSpritePhysicsImpulse(ship.sprID, x#, y#, ship.rvx, ship.rvy)
                endif
EndFunction

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ProfVersaggi

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Joined: 6th Apr 2012

Location: Maastricht Netherlands / Chicago, USA

Posted: 28th Feb 2013 23:53

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Thinking in terms of Math, particularly Trigonometry - the Pythagorean Theorem is useful if the calculations can be made.

h2 = a2 + b2
h = sqrt(a2+b2)

Objective: Determine side 'a' and 'b'.
We know the angle of "h" is the angle of the sprite (enemy boat)
We know the other angle has to be 90 degrees (angle opposite 'h')
We know it's a right triangle by definition (so angle opposite 'h' is 90 degrees)

We don't know 'h', 'a' or 'b' directly ... but if 'h' could be determined (which I 'think' is possible, than calculating both 'a' and 'b' would be possible, and then a formula could be constructed.

To make matters more interesting, considering the following:

This sprite is an enemy boat (physics sprite) having just gone through a function that did a PhysicsRayCast between it and it's target, and produced an angle (which the boat was assigned to) which pointed it 'directly' at the target. Thus no need for directional components of the thrust, just thrust...

I have access to:
x#=GetRayCastX()
y#=GetRayCastY()
and the resultant
angle# = ATan(yoffset#/xoffset#)+bias

so that 'might' provide some of the missing information needed.

Any ideas, suggestions, clues?

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ProfVersaggi

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Posted: 1st Mar 2013 00:21

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As a side note: I use SetSpritePhysicsVelocity for torpedo's, bullets, and cannon projectiles propulsion and am happy with the results ... maybe that's an avenue in some way for ship propulsion mechanisms ...

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ProfVersaggi

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Location: Maastricht Netherlands / Chicago, USA

Posted: 1st Mar 2013 11:10

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UPDATE:

OK, I've figured it out, so I'll answer my own question

Here's what I did:

+ Code Snippet


Function PropelEnemyVehicle(object)
    if (GetSpriteExists(object) = EXISTS)
        angle# = GetSpriteAngle(object)           ` Angle
        vx# = enemy_vehicle_speed*Cos(angle#)     ` The vector is in the direction of the angle of the enemy vehicle
        vy# = enemy_vehicle_speed*Sin(angle#)
        SetSpritePhysicsVelocity(object, vx#, vy#)  ` Moves the enemy forward...
    endif
EndFunction


object: is the physics enabled (dynamic) sprite in question 
enemy_vehicle_speed: is a variable that gets set to the speed of the vehicle and can be changed over time.

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ProfVersaggi

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Location: Maastricht Netherlands / Chicago, USA

Posted: 1st Mar 2013 11:14 Edited at: 1st Mar 2013 14:27

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For those of you who are interested ...

Here is the point function that takes a sprite (physics enabled) and points it to a target (another physics enabled sprite).

Combined with the PropelEnemyVehicle() function and you have a bona fide Autonomous Agent "Seek" function ....

Here's the PointAtTarget() Function:

+ Code Snippet


Function PointAtTarget(object, target)

    if (GetSpriteExists(object) = EXISTS)
                          ` **** You *must* use the ByOffset or it won't work ....
        hit = PhysicsRayCast(GetSpriteXByOffset(object), GetSpriteYByOffset(object),GetSpriteXByOffset(target), GetSpriteYByOffset(target))
        if hit = TRUE
            id = GetRayCastSpriteID()       ` Just in case we need it later ...

            x#=GetRayCastX()
            y#=GetRayCastY()

            ` **** Offset = RayCast [Target] minux SpriteByOffset [object]
            xoffset#=x#-GetSpriteXByOffset(object)
            yoffset#=y#-GetSpriteYByOffset(object)

            ` **** Adjustment for angles outside -90 to +90 range: "bias"
            if xoffset# < 0
                bias = 180
            else
                bias = 0
            endif

            angle# = ATan(yoffset#/xoffset#)+bias
            SetSpriteAngle(object, angle#)
        endif
    endif
EndFunction

NOTE: *** Sorry for the multi-posting ... I just found the edit button :-(

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mr_d

DBPro Tool Maker

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Joined: 26th Mar 2007

Location: Somewhere In Australia

Posted: 1st Mar 2013 14:24 Edited at: 1st Mar 2013 14:25

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***sorry, not related to your topic***
please don't quadruple post - that's what the "edit" button is for...

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Ancient Lady

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Location: Anchorage, Alaska, USA

Posted: 1st Mar 2013 16:45

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Thank you for the great set of code. While not necessarily useful in my current WIP, it has great potential. And I can see how it would be useful in the sequel to my WIP (assuming it is a success).

Cheers,
Ancient Lady
AGK Community Tester and AppGameKit Master

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ProfVersaggi

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Location: Maastricht Netherlands / Chicago, USA

Posted: 1st Mar 2013 16:54

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I'm going to be writing the following sets of functions and will post them for you as a library once I'm finished it it'll be useful:

Wander
Seek
Flee
Pursue
Evade
Arrive
Avoid_Obstacke
Flock
Idle
Hide

and a few others ... just let me know

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AppGameKit Classic Chat / Need help establishing Physics forces always directly behind an object - propulsion system.

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AppGameKit Classic Chat / Need help establishing Physics forces always directly *behind* an object - propulsion system.

AppGameKit Classic Chat / Need help establishing Physics forces always directly behind an object - propulsion system.