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• ### Similar Content

• By KarimIO
Hey guys! Three questions about uniform buffers:
1) Is there a benefit to Vulkan and DirectX's Shader State for the Constant/Uniform Buffer? In these APIs, and NOT in OpenGL, you must set which shader is going to take each buffer. Why is this? For allowing more slots?
2) I'm building an wrapper over these graphics APIs, and was wondering how to handle passing parameters. In addition, I used my own json format to describe material formats and shader formats. In this, I can describe which shaders get what uniform buffers. I was thinking of moving to support ShaderLab (Unity's shader format) instead, as this would allow people to jump over easily enough and ease up the learning curve. But ShaderLab does not support multiple Uniform Buffers at all, as I can tell, let alone what parameters go where.
So to fix this, I was just going to send all Uniform Buffers to all shaders. Is this that big of a problem?
3) Do you have any references on how to organize material uniform buffers? I may be optimizing too early, but I've seen people say what a toll this can take.
• By abarnes
Hello All!
I am currently pursuing a degree in video game programming, so far I have completed an intro to programming course and object oriented programming course. Both were taught using C++ as the programming langauge which I know is very popular for game development, but in these classes we do not actually do any game development. I would like to start to build my skills with C++ for game development as that is a common required thing for a job and am looking for ways to do this. Any recommendations such as books to read or youtube videos to watch will be greatly appreciated!
• By Orella
I'm having problems rotating GameObjects in my engine. I'm trying to rotate in 2 ways.
I'm using MathGeoLib to calculate maths in the engine.
First way: Rotates correctly around axis but if I want to rotate back, if I don't do it following the inverse order then rotation doesn't work properly.
e.g:
Rotate X axis 50 degrees, Rotate Y axis 30 degrees -> Rotate Y axis -50 degrees, Rotate X axis -30 degrees. Works.
Rotate X axis 50 degrees, Rotate Y axis 30 degrees -> Rotate X axis -50 degrees, Rotate Y axis -30 degrees. Doesn't.

Code:
void ComponentTransform::SetRotation(float3 euler_rotation) { float3 diff = euler_rotation - editor_rotation; editor_rotation = euler_rotation; math::Quat mod = math::Quat::FromEulerXYZ(diff.x * DEGTORAD, diff.y * DEGTORAD, diff.z * DEGTORAD); quat_rotation = quat_rotation * mod; UpdateMatrix();  } Second way: Starts rotating good around axis but after rotating some times, then it stops to rotate correctly around axis, but if I rotate it back regardless of the rotation order it works, not like the first way.

Code:
void ComponentTransform::SetRotation(float3 euler_rotation) { editor_rotation = euler_rotation; quat_rotation = math::Quat::FromEulerXYZ(euler_rotation.x * DEGTORAD, euler_rotation.y * DEGTORAD, euler_rotation.z * DEGTORAD); UpdateMatrix();  }
Rest of code:
#define DEGTORAD 0.0174532925199432957f void ComponentTransform::UpdateMatrix() { if (!this->GetGameObject()->IsParent()) { //Get parent transform component ComponentTransform* parent_transform = (ComponentTransform*)this->GetGameObject()->GetParent()->GetComponent(Component::CompTransform); //Create matrix from position, rotation(quaternion) and scale transform_matrix = math::float4x4::FromTRS(position, quat_rotation, scale); //Multiply the object transform by parent transform transform_matrix = parent_transform->transform_matrix * transform_matrix; //If object have childs, call this function in childs objects for (std::list<GameObject*>::iterator it = this->GetGameObject()->childs.begin(); it != this->GetGameObject()->childs.end(); it++) { ComponentTransform* child_transform = (ComponentTransform*)(*it)->GetComponent(Component::CompTransform); child_transform->UpdateMatrix(); } } else { //Create matrix from position, rotation(quaternion) and scale transform_matrix = math::float4x4::FromTRS(position, quat_rotation, scale); //If object have childs, call this function in childs objects for (std::list<GameObject*>::iterator it = this->GetGameObject()->childs.begin(); it != this->GetGameObject()->childs.end(); it++) { ComponentTransform* child_transform = (ComponentTransform*)(*it)->GetComponent(Component::CompTransform); child_transform->UpdateMatrix(); } } } MathGeoLib: Quat MUST_USE_RESULT Quat::FromEulerXYZ(float x, float y, float z) { return (Quat::RotateX(x) * Quat::RotateY(y) * Quat::RotateZ(z)).Normalized(); } Quat MUST_USE_RESULT Quat::RotateX(float angle) { return Quat(float3(1,0,0), angle); } Quat MUST_USE_RESULT Quat::RotateY(float angle) { return Quat(float3(0,1,0), angle); } Quat MUST_USE_RESULT Quat::RotateZ(float angle) { return Quat(float3(0,0,1), angle); } Quat(const float3 &rotationAxis, float rotationAngleRadians) { SetFromAxisAngle(rotationAxis, rotationAngleRadians); } void Quat::SetFromAxisAngle(const float3 &axis, float angle) { assume1(axis.IsNormalized(), axis); assume1(MATH_NS::IsFinite(angle), angle); float sinz, cosz; SinCos(angle*0.5f, sinz, cosz); x = axis.x * sinz; y = axis.y * sinz; z = axis.z * sinz; w = cosz; } Any help?
Thanks.
• By owenjr
Hi there!
I am trying to implement a basic AI for a Turrets game in SFML and C++ and I have some problems.
This AI follows some waypoints stablished in a Bezier Courve.
In first place, this path was followed only by one enemy. For this purpose, the enemy has to calculate his distance between his actual position
to the next waypoint he has to pick.
If the distance is less than a specific value we stablish, then, we get to the next point. This will repeat until the final destination is reached. (in the submitting code, forget about the var m_go)

Okay, our problem gets when we spawn several enemies and all have to follow the same path, because it produces a bad visual effect (everyone gets upside another).
In order to solve this visual problem, we have decided to use a repulsion vector. The calculus gets like this:

As you can see, we calculate the repulsion vector with the inverse of the distance between the enemy and his nearest neighbor.
Then, we get it applying this to the "theorical" direction, by adding it, and we get a resultant, which is the direction that
our enemy has to follow to not "collide" with it's neighbors. But, our issue comes here:

The enemys get sepparated in the middle of the curve and, as we spawn more enemys, the speed of all of them increases dramatically (including the enemies that don't calculate the repuslion vector).
1 - Is it usual that this sepparation occours in the middle of the trajectory?
2 - Is it there a way to control this direction without the speed getting affected?
3 - Is it there any alternative to this theory?

I submit the code below (There is a variable in Spanish [resultante] which it means resultant in English):

if (!m_pathCompleted) { if (m_currentWP == 14 && m_cambio == true) { m_currentWP = 0; m_path = m_pathA; m_cambio = false; } if (m_neighbors.size() > 1) { for (int i = 0; i < m_neighbors.size(); i++) { if (m_enemyId != m_neighbors[i]->GetId()) { float l_nvx = m_neighbors[i]->GetSprite().getPosition().x - m_enemySprite.getPosition().x; float l_nvy = m_neighbors[i]->GetSprite().getPosition().y - m_enemySprite.getPosition().y; float distance = std::sqrt(l_nvx * l_nvx + l_nvy * l_nvy); if (distance < MINIMUM_NEIGHBOR_DISTANCE) { l_nvx *= -1; l_nvy *= -1; float l_vx = m_path[m_currentWP].x - m_enemySprite.getPosition().x; float l_vy = m_path[m_currentWP].y - m_enemySprite.getPosition().y; float l_resultanteX = l_nvx + l_vx; float l_resultanteY = l_nvy + l_vy; float l_waypointDistance = std::sqrt(l_resultanteX * l_resultanteX + l_resultanteY * l_resultanteY); if (l_waypointDistance < MINIMUM_WAYPOINT_DISTANCE) { if (m_currentWP == m_path.size() - 1) { std::cout << "\n"; std::cout << "[GAME OVER]" << std::endl; m_go = false; m_pathCompleted = true; } else { m_currentWP++; } } if (l_waypointDistance > MINIMUM_WAYPOINT_DISTANCE) { l_resultanteX = l_resultanteX / l_waypointDistance; l_resultanteY = l_resultanteY / l_waypointDistance; m_enemySprite.move(ENEMY_SPEED * l_resultanteX * dt, ENEMY_SPEED * l_resultanteY * dt); } } else { float vx = m_path[m_currentWP].x - m_enemySprite.getPosition().x; float vy = m_path[m_currentWP].y - m_enemySprite.getPosition().y; float len = std::sqrt(vx * vx + vy * vy); if (len < MINIMUM_WAYPOINT_DISTANCE) { if (m_currentWP == m_path.size() - 1) { std::cout << "\n"; std::cout << "[GAME OVER]" << std::endl; m_go = false; m_pathCompleted = true; } else { m_currentWP++; } } if (len > MINIMUM_WAYPOINT_DISTANCE) { vx = vx / len; vy = vy / len; m_enemySprite.move(ENEMY_SPEED * vx * dt, ENEMY_SPEED * vy * dt); } } } } } else { float vx = m_path[m_currentWP].x - m_enemySprite.getPosition().x; float vy = m_path[m_currentWP].y - m_enemySprite.getPosition().y; float len = std::sqrt(vx * vx + vy * vy); if (len < MINIMUM_WAYPOINT_DISTANCE) { if (m_currentWP == m_path.size() - 1) { std::cout << "\n"; std::cout << "[GAME OVER]" << std::endl; m_go = false; m_pathCompleted = true; } else { m_currentWP++; } } if (len > MINIMUM_WAYPOINT_DISTANCE) { vx = vx / len; vy = vy / len; m_enemySprite.move(ENEMY_SPEED * vx * dt, ENEMY_SPEED * vy * dt); } } }
¡¡Thank you very much in advance!!

• Overview
Welcome to the 2D UFO game guide using the Orx Portable Game Engine. My aim for this tutorial is to take you through all the steps to build a UFO game from scratch.
The aim of our game is to allow the player to control a UFO by applying physical forces to move it around. The player must collect pickups to increase their score to win.
I should openly acknowledge that this series is cheekily inspired by the 2D UFO tutorial written for Unity.
It makes an excellent comparison of the approaches between Orx and Unity. It is also a perfect way to highlight one of the major parts that makes Orx unique among other game engines, its Data Driven Configuration System.
You'll get very familiar with this system very soon. It's at the very heart of just about every game written using Orx.
If you are very new to game development, don't worry. We'll take it nice and slow and try to explain everything in very simple terms. The only knowledge you will need is some simple C++.
I'd like say a huge thank you to FullyBugged for providing the graphics for this series of articles.

What are we making?
Visit the video below to see the look and gameplay of the final game:
Getting Orx
The latest up to date version of Orx can be cloned from github and set up with:
git clone https://github.com/orx/orx.git After cloning, an $ORX environment variable will be created automatically for your system which will help with making game projects much easier. It will also create several IDE projects for your operating system: Visual Studio, Codelite, Code::Blocks, and gmake. These Orx projects will allow you to compile the Orx library for use in your own projects. And the$ORX environment variable means that your projects will know where to find the Orx library.
For more details on this step, visit http://orx-project.org/wiki/en/tutorials/cloning_orx_from_github at the Orx learning wiki.
Setting up a 2D UFO Project
Now the you have the Orx libraries cloned and compiled, you will need a blank project for your game. Supported options are: Visual Studio, CodeLite, Code::Blocks, XCode or gmake, depending on your operating system.
Once you have a game project, you can use it to work through the steps in this tutorial.
Orx provides a very nice system for auto creating game projects for you. In the root of the Orx repo, you will find either the init.bat (for Windows) or init.sh (Mac/Linux) command.
Create a project for our 2D game from the command line in the Orx folder and running:
init c:\temp\ufo or
init.sh ~/ufo Orx will create a project for each IDE supported by your OS at the specified location. You can copy this folder anywhere, and your project will always compile and link due to the \$ORX environment variable. It knows where the libraries and includes are for Orx.
Open your project using your favourite IDE from within the ufo/build folder.
When the blank template loads, there are two main folders to note in your solution:
config src Firstly, the src folder contains a single source file, ufo.cpp. This is where we will add the c++ code for the game. The config folder contains configuration files for our game.
What is config?
Orx is a data driven 2D game engine. Many of the elements in your game, like objects, spawners, music etc, do not need to be defined in code. They can be defined (or configured) using config files.
You can make a range of complex multi-part objects with special behaviours and effects in Orx, and bring them into your game with a single line of code. You'll see this in the following chapters of this guide.
There are three ufo config files in the config folder but for this guide, only one will actually be used in our game. This is:
ufo.ini All our game configuration will be done there.
Over in the Orx library repo folder under orx/code/bin, there are two other config files:
CreationTemplate.ini SettingsTemplate.ini These are example configs and they list all the properties and values that are available to you. We will mainly concentrate on referring to the CreationTemplate.ini, which is for objects, sounds, etc. It's good idea to include these two files into your project for easy reference.
Alternatively you can view these online at https://github.com/orx/orx/blob/master/code/bin/CreationTemplate.ini and here: https://github.com/orx/orx/blob/master/code/bin/SettingsTemplate.ini

The code template
Now to take a look at the basic ufo.cpp and see what is contained there.
The first function is the Init() function.
This function will execute when the game starts up. Here you can create objects have been defined in the config, or perform other set up tasks like handlers. We'll do both of these soon.
The Run() function is executed every main clock cycle. This is a good place to continually perform a task. Though there are better alternatives for this, and we will cover those later. This is mainly used to check for the quit key.
The Exit() function is where memory is cleaned up when your game quits. Orx cleans up nicely after itself. We won't use this function as part of this guide.
The Bootstrap() function is an optional function to use. This is used to tell Orx where to find the first config file for use in our game (ufo.ini). There is another way to do this, but for now, we'll use this function to inform Orx of the config.
Then of course, the main() function. We do not need to use this function in this guide.
Now that we have everything we need to get start, you should be able to compile successfully. Run the program and an Orx logo will appear slowly rotating.

Great. So now you have everything you need to start building the UFO game.

Setting up the game assets
Our game will have a background, a UFO which the player will control, and some pickups that the player can collect.
The UFO will be controlled by the player using the cursor keys.
First you'll need the assets to make the game. You can download the file  assets-for-orx-ufo-game.zip which contains:
The background file (background.png):

The UFO and Pickup sprite images (ufo.png and pickup.png):

And a pickup sound effect (pickup.ogg):
pickup.ogg
Copy the .png files into your data/texture folder
Copy the .ogg file into your data/sound folder.
Now these files can be accessed by your project and included in the game.

Setting up the Playfield
We will start by setting up the background object. This is done using config.
Open the ufo.ini config file in your editor and add the following:

[BackgroundGraphic] Texture = background.png Pivot = center
The BackgroundGraphic defined here is called a Graphic Section. It has two properties defined. The first is Texture which has been set as background.png.
The Orx library knows where to find this image, due to the properties set in the Resource section:

[Resource] Texture = ../../data/texture
So any texture files that are required (just like in our BackgroundGraphic section) will be located in the ../../data/texture folder.
The second parameter is Pivot. A pivot is the handle (or sometimes “hotspot” in other frameworks). This is set to be center. The position is 0,0 by default, just like the camera. The effect is to ensure the background sits in the center of our game window.
There are other values available for Pivot. To see the list of values, open the CreationTemplate.ini file in your editor. Scroll to the GraphicTemplate section and find Pivot in the list. There you can see all the possible values that could be used.
top left is also a typical value.
We need to define an object that will make use of this graphic. This will be the actual entity that is used in the game:

[BackgroundObject] Graphic = BackgroundGraphic Position = (0, 0, 0)
The Graphic property is the section BackgroundGraphic that we defined earlier. Our object will use that graphic.
The second property is the Position. In our world, this object will be created at (0, 0, 0). In Orx, the coordinates are (x, y, z). It may seem strange that Orx, being a 2D game engine has a Z axis. Actually Orx is 2.5D. It respects the Z axis for objects, and can use this for layering above or below other objects in the game.
To make the object appear in our game, we will add a line of code in our source file to create it.
In the Init() function of ufo.cpp, remove the default line:
orxObject_CreateFromConfig("Object"); and replace it with:
orxObject_CreateFromConfig("BackgroundObject"); Compile and run.
The old spinning logo is now replaced with a nice tiled background object.

Next, the ufo object is required. This is what the player will control. This will be covered in Part 2.

# C++ Template specialisation via base class

## Recommended Posts

So as the title (hopefully somewhat) says, I'm trying to achieve a spezialisation of a template class, based on whether or not the template-parameter is derived off of another (templated) class:

// base class, specializations must match this signature
template<typename Object>
class ObjectSupplier
{
public:

static constexpr size_t objectOffset = 1;

static Object& GetClassObject(CallState& state)
{
return *state.GetAttribute<Object>(0);
}
};

// possible specialisation for all "Data"-classes,
// which are actually derived classes using CRTP
template<typename Derived>
class ObjectSupplier<ecs::Data<Derived>>
{
public:

static constexpr size_t objectOffset = 1;

static Derived& GetClassObject(CallState& state)
{
return state.GetEntityAttribute(0)->GetData<Derived>();
}
};

// ... now here's the problem:

// this would work ...
ObjectSupplier<ecs::Data<Transform>>::GetClassObject(state);
// unfornately the actual object is "Transform", which is merely derived
// of "ecs::Data<Transform>" and thus it calls the incorrect overload
ObjectSupplier<Transform>::GetClassObject(state);

The last two lines show the actual problem. I'm using this ObjectSupplier-class as part of my script-binding system, and thus its not possible/feasable to input the required base-class manually:

template<typename Return, typename Class, typename... Args>
void registerBindFunction(ClassFunction<Return, Class, Args...> pFunction, sys::StringView strFilter, std::wstring&& strDefinition)
{
using Supplier = ObjectSupplier<Class>;
using RegistryEntry = BindFunctionRegistryEntry<ClassFunctionBindCommand<Supplier, Class, Return, Args...>>;

registerClassBindEntry<RegistryEntry, Supplier, Return, Args...>(pFunction, false, strFilter, std::move(strDefinition), DEFAULT_INPUT, DEFAULT_OUTPUT);
}

registerBindFunction(&GenericObject::Func, ...);
// needs to access the ObjectSupplier<ecs::Data<Derived>> overload
registerBindFunction(&Transform::GetAbsoluteTransform, ...);

// thats how it used to be before:

registerObjectBindFunction(&GenericObject::Func, ...);
// a few overloads that internally used a "EntityDataSupplier"-class
registerEntityDataBindFunction(&GenericObject::GetAbsoluteTransform, ...);

(well, it were possible, but I want this binding-code to be as simple as humanly possible; which is why I'm trying to not have to manually specify anything other than "I want to bind a function here").

So, thats the gist of it. Any ideas on how to get this to work? I don't want to (again) have to create manual overloads for "registerBindFunctions", which there would have to be at least 5 (and all have a complex signature); but I'm certainly open to different approaches, if what I'm trying to achieve via template specialization isn't possible.

Thanks!

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This is as close as I was able to get:

I'm not sure if you're able to get rid Type in the base class, since you need access to that type in the specialization to determine if T is a derived class. However someone else with better template-foo can certainly prove me wrong

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Ah, seems promising! I actually tried SFINEA/enable_if, but didn't know how to put it base-struct. Putting the "Type" as part of the base class is not a problem, I'll have to try it out later, but thanks so far

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I'm not sure how many specializations you want to have for Object Supplier, but if you only want to support ecs::Data types as the specialization, and everything else to use the standard template, then you can just use std::conditional when declaring the Supplier type in registerBindFunction to select the ecs::Data type:

using Supplier = ObjectSupplier<typename std::conditional<std::is_base_of<ecs::Data<Class>, Class>::value, ecs::Data<Class>, Class>::type;

If you don't mind creating a single new overload for registerBindFunction then you can template the above to get rid of the explicit ecs::Data type if you want to support any other wrapped/CRTP base classes.

Otherwise, you can use Zipsters approach. You can also attempt to use the type directly in registerBindFunction instead of using enable_if. Not sure how much sense that makes since I'm making this up as I go, but:

using Supplier = ObjectSupplier<Class::UnderlyingType>;

Of course, now you need to make sure any class used with ObjectSupplier has that type, which I'm not particularly happy about. You can use some macro to simplify it, or you can make it more explicit by requiring a new derived class that handles it for you:

template <typename Object>
{
using UnderlyingType = Object;
};

namespace ecs
{
template <typename T>
{
};
}

Or something like that, which makes the relationship to ObjectSupplier more clear. But I'm still not too fond of it because it involves even more boilerplate and adds complexity to the usage of ObjectSupplier (now you need the Receiver class base...). However you can use ObjectReceiver directly in registerBindFunction and statically assert that the type input is derived from it, which gives you a way to guarantee its use with a clear error message.

That said, if you have some common function in your classes, then you can also completely bypass the need to provide that base type with a little bit of metaprogramming:

template<typename T, typename R>
T BaseOf(R T::*);

// baseFunc is a common function in your base class, or some such
using Supplier = ObjectSupplier<decltype(BaseOf(&Class::baseFunc))>;

If this is enough, then you won't even need to add Type to the base, and all is well (you still need some consistent function or variable to point at to deduce the type of the base class though).

There are probably more complex ways of getting the base type without requiring such a thing as "baseFunc", but I haven't looked into it much.

This is all just off the top of my head stuff. std::conditional would be the simplest but Zipsters approach is probably more scalable.

Unfortunately I don't have time to exercise "real template-foo" to get around the type declaration, but frankly it's not that important. The above is just food for thought (i.e. I wrote it up while I was eating a midnight snack, code probably doesn't even compile :P).

Edited by Styves

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What do you expect the function to look like when passing a "ObjectSupplier" class that seems to me as if you want some type of anonymous objects passing into your script, is it?

Either you create a fixed base class any of your bind function parameter has to inherit from or if that is not in your intention just try to restructure your "ObjectSupplier" class where maybe the solution would be to make some kind of anonymous type wrapping structure that also delivers the necessary informations to your binder function. Some time ago, I added a C# like object struct to my engine code (but never used it since ) to achive exactly this. Passing any type into it with an inner template abstraction while the outer struct is absolutely aware of

struct object
{
private:
struct AbstractType
{
virtual void Free(void** ptr, Allocator& allocator) = 0;

virtual void CopyByVal(void const* src, void** dest) = 0;
virtual void CopyByRef(void* const* src, void** dest) = 0;

virtual void* Value(void** ptr) = 0;

virtual const type_info& GetType() = 0;
virtual uint32 Size() = 0;
};
template<typename T> struct val_type : AbstractType
{
//override for value types here that fit into sizeof(void*)
};
template<typename T> struct ref_type : AbstractType
{
//override for ref types here that do not fit into sizeof(void*) or const char*
};

//do some pointer magic
template<typename T> static AbstractType* DiffType()
{
if(sizeof(T) <= sizeof(void*))
{
/**
the passed value matches into a pointer address memory block so use it directly
instead of creating a pointer based accessing manager. This saves a lot of memory.
*/
static val_type<T> handler;
return &handler;
}
else
{
static ref_type<T> handler;
return &handler;
}
};

AbstractType* handler; //an interface to the underlaying value
void* value; //the memory address hold value is stored

public:
inline object& Assign(object const& obj)
{
Clear();

handler = obj.handler;
if(handler) handler->CopyByRef(&obj.value, &value, GetAllocator());

return *this;
}
template<typename T> inline object& Assign(T const& ptr)
{
if(handler) handler->Free(&value, GetAllocator());

handler = DiffType<T>();
handler->CopyByVal(&ptr, &value, GetAllocator());

return *this;
}

template<typename T> inline T Cast()
{
if(!handler) return typename const_trait<T>::type();

T* r = reinterpret_cast<T*>(handler->Value(&value));
return *r;
}
template<typename T> inline bool TryCast(T& ptr)
{
if(!handler || handler->GetType() != typeof(T))
return false;

ptr = *reinterpret_cast<T*>(handler->Value(&value));
return true;
}

template<typename T> inline bool Is() { return (GetType() == typeof(T)); }
inline const std::type_info& GetType() { return ((handler) ? handler->GetType() : typeof(void)); }

inline const uint32 Size() { return ((handler) ? handler->Size() : 0); }

inline void Clear()
{
if(handler) handler->Free(&value);
handler = 0;
}
};

Left out some (I lied, a lot) of construction and operator code but reduced the basic mechanisms to the core ones to illustrate how it works. You add your any kind value into this cointainer as an anonymous plain pointer for the type erasure and add some kind of overhead information class to it additionally. Any template parameter is abstracted out by inheriting from an untemplated base class offering an interface but the deriving class will override it and so have access to the original type T again.

I added two types of those overhead classes where the value type one treats the passed pointer "as is" (usefull for saving an allocation for small types and primitives such as bool, char, int ...) while the reference type one allocates a copy of the passed memory address (so you may create an object from a type on stack without playing with invalid pointers when stack got cleared) for the cost of only two pointers

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7 hours ago, Styves said:

I'm not sure how many specializations you want to have for Object Supplier, but if you only want to support ecs::Data types as the specialization, and everything else to use the standard template, then you can just use std::conditional when declaring the Supplier type in registerBindFunction to select the ecs::Data type:

There are actually many more suppliers, which I want to be able to declare/add at different modules w/o affecting the code using it.

7 hours ago, Styves said:

Otherwise, you can use Zipsters approach. You can also attempt to use the type directly in registerBindFunction instead of using enable_if. Not sure how much sense that makes since I'm making this up as I go, but:

I don't think that would work, enable_if is used for SFINEA and probably required to only compile the specialization when the condition is actually met.

7 hours ago, Styves said:

Or something like that, which makes the relationship to ObjectSupplier more clear. But I'm still not too fond of it because it involves even more boilerplate and adds complexity to the usage of ObjectSupplier (now you need the Receiver class base...). However you can use ObjectReceiver directly in registerBindFunction and statically assert that the type input is derived from it, which gives you a way to guarantee its use with a clear error message.

Deriving the classes used for specialization is not a (good) option; first of all I try to minimze inheritance anyways and prefer external solutions via such "traits" normally; also there's a specific non-templated version for a large range of base-objects, which really should not have to be derived, if that makes any sense.

8 hours ago, Styves said:

If this is enough, then you won't even need to add Type to the base, and all is well (you still need some consistent function or variable to point at to deduce the type of the base class though).

I'm going to post my actual solution at the end of this post, where you should see that I don't even need to add "Type" to the base at all, even in Zipsters solution

2 hours ago, Shaarigan said:

What do you expect the function to look like when passing a "ObjectSupplier" class that seems to me as if you want some type of anonymous objects passing into your script, is it?

The ObjectSupplier is there to handle object-aquision for the script-calls. Long story short, I'm using a visual scripting system that is rather high level, and I want to be able to call certain functions w/o first having to aquire the actual C++-object (the type system won't even know it exists). Enter ObjectSupplier, which in case of my example will tell the script-system: "In case you bind a function of a ecs::Data<>-object, the function in script should take a Entity-reference instead and aquire the data-object off that before calling the function-pointer.
A function using tihs might look like that:

void Call(double dt)
{
CallState callState(*this);
Class& object = Supplier::GetClassObject(callState);

ClassCallHelper<false, Supplier, Class, Function, Return, Args...>::Call(object, m_pFunction, callState);
}

Now depending on the specialization of Supplier, it will eigther just get the actual object from Stack; or do something completely different as the specialization dictates. (if thats what you asked)

2 hours ago, Shaarigan said:

Either you create a fixed base class any of your bind function parameter has to inherit from or if that is not in your intention just try to restructure your "ObjectSupplier" class where maybe the solution would be to make some kind of anonymous type wrapping structure that also delivers the necessary informations to your binder function. Some time ago, I added a C# like object struct to my engine code (but never used it since ) to achive exactly this. Passing any type into it with an inner template abstraction while the outer struct is absolutely aware of

Haven't dealt with type-erasure much I think though, and I'm not sure if that would actually be superior to the current solution Zipster offered, but I'll have a proper read of it later, thanks

As for the solution I ended up using: Its pretty much as zipster wrote, just a tad simpler:

// base supplier
template<typename Object, typename Enable = void>
class ObjectSupplier
{
public:

static Object& GetClassObject(CallState& state)
{
return *state.GetAttribute<Object>(0);
}
};

template<bool Test>
using EnableIf = typename std::enable_if<Test>::type;

template<typename T, typename T2>
using CheckIsBase = EnableIf<std::is_base_of<T, T2>::value>;

template<typename Derived>
class ObjectSupplier<Derived, sys::CheckIsBase<ecs::Data<Derived>, Derived>>
{
public:

static Derived& GetClassObject(CallState& state)
{
return state.GetEntityAttribute(0)->GetData<Derived>();
}
};

sys::CheckIsBase is a typedef based on a typedef of std::enable_if using is_base_of, that I've actually been using for some time now. Also, as you can see I don't have to use Derived::Type, but can just use Derived directly. Which makes sense, if I added Type to ecs::Data<Derived>, Type would just be "Derived" in the end, which I don't have to lookup, since its already part of the template.

One problem I had is that ou can only use enable_if with no custom type supplies as second template parameter (my typedef used "int" as a default) for some reason, otherwise it will fail to correctly specialize. Other than that, this solution is pretty perfect especially since I don't have to add "Type" to the base classes; it allows me to add the ObjectSuppliers away from the code that uses it, and it also lets me add specialization based on different traits (ie. I have a "isBaseObject<>" trait for my type-system which doesn't involve inheritance).
So thanks to Zipster for providing me this neat solution, and thanks to everyone for their input