How are components in larger game engines implemented?

[StackMasher]

A lot of games allow you to choose multiple renderers, input libraries etc but how do they do this? I'm thinking they would have to have some sort of a standardized interface for each component, but if-else statements would probably add a lot of overhead and all the components are statically linked with the main game

 

[catlover007]

In most cases(I know of), interfaces with static or dynamic dispatch are used.
To illustrate this, here is bit of Java/C++ mix like pseudo code

Solution #1, using dynamic dispatch:

interface Renderer {
RenderThis()
RenderThat()
}

class RendererDirectX implements Renderer{
...
}

class RendererOpenGL implements Renderer{
...
}

if(options.renderer == "directx"){
renderer = new RendererDirectX();
}else{
renderer = new RendererOpenGL();
}

Solution #2, using static dispatch(which is more performant, but the destination needs to known at compile time):

class Renderer {
#ifdef PLATFORM_WII
Renderer rendererImpl = new RendererWii();
#else
Renderer rendererImpl = new RendererOpenGL();
#endif

RenderThis() {
rendererImpl.renderThis();
}

RenderThat() {
rendererImpl.renderThat();
}
}

If you are more familiar with C++, a interface is basically a class containing only pure virtual methods

 

[StackMasher]

In most cases(I know of), interfaces with static or dynamic dispatch are used.
To illustrate this, here is bit of Java/C++ mix like pseudo code

Solution #1, using dynamic dispatch:

interface Renderer {
RenderThis()
RenderThat()
}

class RendererDirectX implements Renderer{
...
}

class RendererOpenGL implements Renderer{
...
}

if(options.renderer == "directx"){
renderer = new RendererDirectX();
}else{
renderer = new RendererOpenGL();
}

Solution #2, using static dispatch(which is more performant, but the destination needs to known at compile time):

class Renderer {
#ifdef PLATFORM_WII
Renderer rendererImpl = new RendererWii();
#else
Renderer rendererImpl = new RendererOpenGL();
#endif

RenderThis() {
rendererImpl.renderThis();
}

RenderThat() {
rendererImpl.renderThat();
}
}

If you are more familiar with C++, a interface is basically a class containing only pure virtual methods

awesome thanks