B4A Library libGDX - Game Engine

wonder · Dec 11, 2014

Does this library work with B4J? In other words, can I create PC games using B4J + libGDX?

Informatix · Dec 11, 2014

wonder said:
Does this library work with B4J? In other words, can I create PC games using B4J + libGDX?

No.

Peter Simpson · Dec 11, 2014

I really want to get into the LibGDX library.
I take one look at this library and I think to myself, going to medical college to learn brain surgery would probably be a lot easier

I really have to take a few days to learn the basics one day...

wonder · Dec 11, 2014

If you take baby steps it's not really that hard.

Try starting by rendering a texture and moving it on screen.

inakigarm · Dec 11, 2014

Peter Simpson said:
I really want to get into the LibGDX library.
It I take one look at this library and I think to myself, going to medical college to learn brain surgery would probably be a lot easier
I really have to take a few days to learn the basics one day...

walterf25 · Dec 23, 2014

Hello everyone, i was wondering if anyone could help me figure something out, i've done libgdx games, but only using Scene2d, now i'm working on a game which uses both Scene2d and Box2d, i've read tons of threads about this issue but don't understand a damn thing, lol.

How can i figure out the coordinates for a physics body and apply a texture to the body, and move the texture to the same position the physics body is moving?

so far I have the texture drawn on the scened2d stage and my physics body but the texture gets drawn far away from the physics body.

Any one?

Thanks,
Walter

Informatix · Dec 24, 2014

walterf25 said:
Hello everyone, i was wondering if anyone could help me figure something out, i've done libgdx games, but only using Scene2d, now i'm working on a game which uses both Scene2d and Box2d, i've read tons of threads about this issue but don't understand a damn thing, lol.

How can i figure out the coordinates for a physics body and apply a texture to the body, and move the texture to the same position the physics body is moving?

so far I have the texture drawn on the scened2d stage and my physics body but the texture gets drawn far away from the physics body.

Any one?

Thanks,
Walter

You have a very simple example provided with the library (Box2D_PhysicsBodyEditorLoader) and I already saw in this forum a more advanced example showing a bottle filled with balls; you should try to find it.

wonder · Jan 10, 2015

Hello again Informatix,

Here's a somewhat generic question.
I usually initialize lgdx as a view and handle the "normal" stuff like, panels, labels and so on, inside a timer event. The code goes something like this:

B4X:

Sub Activity_Create(FirstTime As Boolean)
    (...)

    'Initialize libGDX
    GLView = lGdx.InitializeView("LG")
    Activity.AddView(GLView, 0%x, 0%y, 100%x, 100%y)

    (...)

    Auxiliary_Engine_Stuff.BringToFront 'All the panels, labels and so on...

    Auxiliary_Engine.Initialize("Auxiliary_Engine", 16)
    Auxiliary_Engine.Enabled = True
End Sub

Sub Auxiliary_Engine_Tick
    'Handle "normal" stuff
End Sub

Sub LG_Render
    'Handle graphics, sound, logic, math and everything else that doesn't crash my program
End Sub

As I understood from your tutorial, LibGDX runs on a different thread from the main activity one.

Informatix said:
You cannot use the debugger of B4A with libGDX because most of the code of the library runs in a different thread.

It comes under my impression that everything happens faster inside LG_Render rather than inside of Auxiliary_Engine_Tick, but I don't know if this is only my imagination.

So my question is:
Is there a performance advantage on running more complex mathematical operations, for example calculations between matrices, in the GDX thread?
For example in my Asus tablet, is the code a = ((b * c) / d) being handled by the Quad-core 1.2 GHz Cortex-A7 CPU when running inside the "auxiliary engine",
instead of being handled by the PowerVR SGX544 GPU, if ran inside LG_Render?

I'm sorry if this is a dumb question.

Informatix · Jan 10, 2015

wonder said:
Hello again Informatix,

Here's a somewhat generic question.
I usually initialize lgdx as a view and handle the "normal" stuff like, panels, labels and so on, inside a timer event. The code goes something like this:

B4X:

Sub Activity_Create(FirstTime As Boolean) (...) 'Initialize libGDX GLView = lGdx.InitializeView("LG") Activity.AddView(GLView, 0%x, 0%y, 100%x, 100%y) (...) Auxiliary_Engine_Stuff.BringToFront 'All the panels, labels and so on... Auxiliary_Engine.Initialize("Auxiliary_Engine", 16) Auxiliary_Engine.Enabled = True End Sub Sub Auxiliary_Engine_Tick 'Handle "normal" stuff End Sub Sub LG_Render 'Handle graphics, sound, logic, math and everything else that doesn't crash my program End Sub

As I understood from your tutorial, LibGDX runs on a different thread from the main activity one.

It comes under my impression that everything happens faster inside LG_Render rather than inside of Auxiliary_Engine_Tick, but I don't know if this is only my imagination.

So my question is:
Is there a performance advantage on running more complex mathematical operations, for example calculations between matrices, in the GDX thread?
For example in my Asus tablet, is the code a = ((b * c) / d) being handled by the Quad-core 1.2 GHz Cortex-A7 CPU when running inside the "auxiliary engine",
instead of being handled by the PowerVR SGX544 GPU, if ran inside LG_Render?

I'm sorry if this is a dumb question.

I don't understand why you want to use a timer while you have the Render event at your disposal (synchronizing your views with libGDX is probably cumbersome and not reliable at all). The Render event is raised by the OpenGL driver, so it is raised ASAP to feed the hardware with data. If you do nothing, it is triggered at the maximum rate of your display (in most cases: about 60 fps). The timer tick event is not at all in this case and becomes very unreliable when you set a low interval (even if you do nothing).
Your computations in B4A are always done by the CPU. The code of your shaders, on the contrary, is run by the GPU.

wonder · Jan 10, 2015

Informatix said:
I don't understand why you want to use a timer while you have the Render event at your disposal (synchronizing your views with libGDX is probably cumbersome and not reliable at all). The Render event is raised by the OpenGL driver, so it is raised ASAP to feed the hardware with data. If you do nothing, it is triggered at the maximum rate of your display (in most cases: about 60 fps). The timer tick event is not at all in this case and becomes very unreliable when you set a low interval (even if you do nothing).

Thank you very much for the explanation, Fred!! I will start using lgdx.CallSubUI() instead and ditch the timers.

Informatix said:
Your computations in B4A are always done by the CPU. The code of your shaders, on the contrary, is run by the GPU.

...and this answers my question. Thanks again. Everything's clear now.

TheJinJ · Jan 12, 2015

I was just looking through an old folder of test projects and came across a RUBE to Box2D export I wrote last summer. RUBE is a cool editor that allows you to plot shapes, points etc, you can then export as a json file. Using this in B4J(or B4A if you like) it will create the needed code for use in B4A.
Tested and mostly worked, may be handy for someone

RUBE

TheJinJ · Jan 17, 2015

I've been experimenting and can't find a way to make userdata work for me to pass the sprite object with each body. Do you have an example how it works? Would be appreciated.

Cheers

Informatix · Jan 18, 2015

TheJinJ said:
I've been experimenting and can't find a way to make userdata work for me to pass the sprite object with each body. Do you have an example how it works? Would be appreciated.

Cheers

In the Box2D_PhysicsBodyEditorLoader demo, if you set the UserData of Bodies(i) to Sprites(i) in LG_Create, you can retrieve the sprite later without issue.

TheJinJ · Jan 18, 2015

I can pass the object OK but can't access any of it's properties. I'll have another go tonight when I'm back in. Cheers

Informatix · Jan 18, 2015

TheJinJ said:
I can pass the object OK but can't access any of it's properties. I'll have another go tonight when I'm back in. Cheers

I don't understand. If you expect to be able to do something like UserData.Color=... that cannot work because UserData is a generic object. UserData is not of the lgSprite type. You use it to keep a reference to an object (as you do with Tag for your views). If you want to be able to use the stored Sprite, you have to do something like: Dim MySprite as lgSprite = myBody.UserData. So the object gets a type.

TheJinJ · Jan 18, 2015

I was creating a new sprite and making it equal to the userdata as you suggested, I must be doing something daft wrong so I'll have another look.

Informatix said:
I don't understand. If you expect to be able to do something like UserData.Color=... that cannot work because UserData is a generic object. UserData is not of the lgSprite type. You use it to keep a reference to an object (as you do with Tag for your views). If you want to be able to use the stored Sprite, you have to do something like: Dim MySprite as lgSprite = myBody.UserData. So the object gets a type.

TheJinJ · Jan 18, 2015

I have a feeling this is something obvious but this throws an error. If I reference the sprite directly it works fine.

B4X:

body0.createFixture(fixtureDef).UserData = image0

B4X:

    Dim MySprite As lgSprite = body0.UserData
    bvec2 = body0.Position
    MySprite.SetPosition(bvec2.x - MySprite.Width /2, bvec2.y - MySprite.Height /2)
    MySprite.SetOriginCenter
    MySprite.Rotation = body0.Angle * lgmu.radiansToDegrees

B4X:

sb.Begin

    MySprite.Draw(sb)

sb.End

null object reference

Informatix said:
I don't understand. If you expect to be able to do something like UserData.Color=... that cannot work because UserData is a generic object. UserData is not of the lgSprite type. You use it to keep a reference to an object (as you do with Tag for your views). If you want to be able to use the stored Sprite, you have to do something like: Dim MySprite as lgSprite = myBody.UserData. So the object gets a type.

Informatix · Jan 19, 2015

TheJinJ said:
I have a feeling this is something obvious but this throws an error. If I reference the sprite directly it works fine.

B4X:

body0.createFixture(fixtureDef).UserData = image0

B4X:

Dim MySprite As lgSprite = body0.UserData bvec2 = body0.Position MySprite.SetPosition(bvec2.x - MySprite.Width /2, bvec2.y - MySprite.Height /2) MySprite.SetOriginCenter MySprite.Rotation = body0.Angle * lgmu.radiansToDegrees

B4X:

sb.Begin MySprite.Draw(sb) sb.End

null object reference

Are you sure that the original Sprite is initialized? and is not destroyed before using it?

TheJinJ · Jan 19, 2015

Informatix said:
Are you sure that the original Sprite is initialized? and is not destroyed before using it?

Yes, if I used 'image0' in place of 'Mysprite' it would work ok

Informatix · Jan 19, 2015

TheJinJ said:
Yes, if I used 'image0' in place of 'Mysprite' it would work ok

Then send me your project because there's no obvious reason.

B4A Library libGDX - Game Engine

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