Para mas información vea tutoriales básicos, creación básica de objetos y trabajo con relojes.

Las propiedades de los objetos como: posiciones, escalas y rotación son almacenadas en las estructura orxFrame.
Estos marcos estan juntos en la jerarquia de gráficos, lo que significa que las propiedades del marco padre afectarán las propiedades de sus hijos.

En este tutorial, tenemos 4 objetos que serán vinculados a un padre en común ¹⁾ y un quinto sin padre.
Los dos primeros hijos son creados usando las propiedades de objetos de la configuración ChildList mientras que los otros dos son creados y vínculados desde el código (por propositos didácticos).
El objeto padre invisible seguira el puntero del ratón. Las teclas “SHIFT IZQUIERDA” y “CONTROL IZQUIERDA” cambiarán la escala arriba y abajo del objeto padre, mientras que el click “IZQUIERDO” y “DERECHO” lo harán rotar.
Todas estas transformaciones afectaran a los 4 hijos.

Esto nos muestra una forma fácil de crear grupos de objetos complejos y transformar sus propiedades (posición, escala, rotación, vélocidad…) fácilmente.

As with the previous tutorials, we begin by loading our config file and creating a viewport.

orxConfig_Load("../03_Frame.ini");
 
orxViewport_CreateFromConfig("Viewport");

We then create our parent object.

pstParentObject = orxObject_CreateFromConfig("ParentObject");

As in the config file, for our ParentObject we defined:

[ParentObject]
ChildList = Object3 # Object4

Thus when we create our parent object, those two children ²⁾ have also been automagically created and linked.
We could have done so for all the four children, but, for a learning purpose, we'll create the two remaining children in code and link them manually.

orxOBJECT *pstObject;
orxObject_CreateFromConfig("Object0");
pstObject = orxObject_CreateFromConfig("Object1");
orxObject_SetParent(pstObject, pstParentObject);
pstObject = orxObject_CreateFromConfig("Object2");
orxObject_SetParent(pstObject, pstParentObject);

Here, Object0 is our static object: the only one that won't be linked to our ParentObject.

Please note that when we create and link manually objects in code, it's our responsability to delete them. On the contrary, Object3 and Object4 will be automatically deleted when ParentObject will be deleted.

We then create a 100Hz clock and register our Update function to it. This function is where we'll manage the inputs to scale/rotate the ParentObject and make sure it'll follow our mouse cursor.

pstClock = orxClock_Create(orx2F(0.01f), orxCLOCK_TYPE_USER);
 
orxClock_Register(pstClock, Update, orxNULL, orxMODULE_ID_MAIN, orxCLOCK_PRIORITY_NORMAL);

Let's now have a look to our Update function.
First, we make sure we can find the position in our world space that corresponds to our mouse cursor in the screen space.
We then copy our ParentObject Z coordinate (ie. we keep the same depth as before) over it and we finally set it back on our ParentObject.

if(orxRender_GetWorldPosition(orxMouse_GetPosition(&vPosition), &vPosition))
{
  orxVECTOR vParentPosition;
  orxObject_GetWorldPosition(pstParentObject, &vParentPosition);
  vPosition.fZ = vParentPosition.fZ;
  orxObject_SetPosition(pstParentObject, &vPosition);
}

The only thing left to do is to apply scale and rotation according to our inputs.
In our case, we defined the following inputs in 03_Frame.ini: RotateLeft, RotateRight, ScaleUp and ScaleDown.

Let's see how we handle them. First, the rotations.

if(orxInput_IsActive("RotateLeft"))
{
  orxObject_SetRotation(pstParentObject, orxObject_GetRotation(pstParentObject) + orx2F(-4.0f) * _pstClockInfo->fDT);
}    
if(orxInput_IsActive("RotateRight"))
{
  orxObject_SetRotation(pstParentObject, orxObject_GetRotation(pstParentObject) + orx2F(4.0f) * _pstClockInfo->fDT);
}

And now, the scales.

if(orxInput_IsActive("ScaleUp"))
{
  orxObject_SetScale(pstParentObject, orxVector_Mulf(&vScale, orxObject_GetScale(pstParentObject, &vScale), orx2F(1.02f)));
}
if(orxInput_IsActive("ScaleDown"))
{
  orxObject_SetScale(pstParentObject, orxVector_Mulf(&vScale, orxObject_GetScale(pstParentObject, &vScale), orx2F(0.98f)));
}

That's all! Our ParentObject will be updated and all his children with it.

NB:

• We could have used config values instead of constants for the rotation and scale values. This way, we could change them without having to recompile and even update them in real time by pressing BackSpace. ³⁾
• As we use the clock's DT for the rotations, they will benefit from time consistency ⁴⁾. Unfortunately, that won't be the case for the scales. (Which is usually something we really don't want!)

Código fuente: 03_Frame.c

Fichero de configuración: 03_Frame.ini