magnum/doc/platform.dox

/*
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    Copyright © 2010, 2011, 2012, 2013 Vladimír Vondruš <mosra@centrum.cz>

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namespace Magnum { namespace Platform {
/** @page platform Platform support
@brief Integration into windowing toolkits and creation of windowless contexts.

-   Next page: @ref types

@ref Platform namespace contains classes integrating %Magnum engine into
various toolkits, both windowed and windowless. Each class has slightly
different dependencies and platform requirements, see documentation of
@ref Platform namespace and particular `*Application` classes for more
information about building and usage with CMake.

@tableofcontents

All the classes have common API to achieve static polymorphism, so basically
you can use different toolkits on different platforms and the only thing you
need to change is the class name, everything else is the same. Basic usage is
to subclass the chosen `*Application` class and implement required methods.

@section platform-windowed Windowed applications

Windowed applications provide a window and keyboard and mouse handling. The
most basic toolkit (and toolkit packaged for most systems) is GLUT, which is
implemented in @ref Platform::GlutApplication. As said above, the usage is
similar for all toolkits, you must provide one-argument constructor and
implement at least @ref GlutApplication::viewportEvent() "viewportEvent()" and
@ref GlutApplication::drawEvent() "drawEvent()". The class can be then used
directly in `main()`, but for convenience and portability it's better to use
@ref MAGNUM_GLUTAPPLICATION_MAIN() macro.

To simplify the porting, the library provides `Platform::Application` typedef
and `MAGNUM_APPLICATION_MAIN()` macro (but only if only one application header
is included, to avoid ambiguity). Changing the code to use different toolkit is
then matter of replacing only the <tt>#</tt>`include` statement (and changing
one line in CMake build script, as you see later).

Barebone application implementation which will just clear the window to dark
blue color is shown in the following code listing.

@note Fully contained base application along with CMake setup is available in
    `base` branch of [Magnum Bootstrap](https://github.com/mosra/magnum-bootstrap)
    repository.

@code
#include <Color.h>
#include <DefaultFramebuffer.h>
#include <Renderer.h>
#include <Platform/GlutApplication.h>

using namespace Magnum;

class MyApplication: public Platform::Application {
    public:
        MyApplication(const Arguments& arguments);

    private:
        void viewportEvent(const Vector2i& viewport) override;
        void drawEvent() override;
};

MyApplication::MyApplication(const Arguments& arguments): Platform::Application(arguments) {
    // Set clear color to dark blue
    Renderer::setClearColor({0.0f, 0.0f, 0.4f});
}

void MyApplication::viewportEvent(const Vector2i& size) {
    // Resize the framebuffer to new window size
    defaultFramebuffer.setViewport({{}, size});
}

void MyApplication::drawEvent() {
    // Clear the window
    defaultFramebuffer.clear(DefaultFramebuffer::Clear::Color);

    // The context is double-buffered, swap buffers
    swapBuffers();
}

// main() function implementation
MAGNUM_APPLICATION_MAIN(MyApplication)
@endcode

@section platform-windowless Windowless applications

Windowless applications provide just a context for ofscreen rendering or
performing tasks on GPU. There is not yet any platform-independent toolkit
which could handle this in portable way, thus you have to use platform-specific
ones. As example we use @ref Platform::WindowlessGlxApplication, you need to
implement just @ref WindowlessGlxApplication::exec() "exec()" function. The
class can be then used directly in `main()`, but again, for convenience and
portability it's better to use @ref MAGNUM_WINDOWLESSGLXAPPLICATION_MAIN()
macro.

Similarly as with windowed applications, to simplify the porting, the library
provides `Platform::WindowlessApplication` typedef and `MAGNUM_WINDOWLESSAPPLICATION_MAIN()`
macro, but only if only one windowless application header is included. Changing
the code to use different toolkit is then matter of replacing only the
<tt>#</tt>`include` statement. Aliases for windowless applications are
separated from aliases for windowed applications, because projects commonly
contain both graphics application and command-line tools (for data preparation
etc.).

Barebone application which will just print out current OpenGL version and
renderer string and exits is in the following code listing.

@note Fully contained windowless application along with CMake setup is
    available in `windowless` branch of [Magnum Bootstrap](https://github.com/mosra/magnum-bootstrap)
    repository.

@code
#include <Context.h>
#include <Platform/WindowlessGlxApplication.h>

using namespace Magnum;

class MyApplication: public Platform::WindowlessApplication {
    public:
        MyApplication(const Arguments& arguments);

        int exec() override;
};

MyApplication::MyApplication(const Arguments& arguments): Platform::WindowlessApplication(arguments) {}

int MyApplication::exec() {
    Debug() << "OpenGL version:" << Context::current()->versionString();
    Debug() << "OpenGL renderer:" << Context::current()->rendererString();

    // Exit with success
    return 0;
}

// main() function implementation
MAGNUM_WINDOWLESSAPPLICATION_MAIN(MyApplication)
@endcode

@section platform-compilation Compilation with CMake

Barebone compilation consists just of finding %Magnum library with required
`*Application` component, adding %Magnum's `${MAGNUM_INCLUDE_DIRS}` and application-specific `${MAGNUM_GLUTAPPLICATION_INCLUDE_DIRS}` to include path, compilation of the
executable and linking `${MAGNUM_LIBRARIES}` and `${MAGNUM_GLUTAPPLICATION_LIBRARIES}`
to it.

Again, to simplify porting, you can also use generic `${MAGNUM_APPLICATION_INCLUDE_DIRS}`
and `${MAGNUM_WAPPLICATION_LIBRARIES}` aliases (or `${MAGNUM_WINDOWLESSAPPLICATION_INCLUDE_DIRS}`, `${MAGNUM_WINDOWLESSAPPLICATION_LIBRARIES}` for windowless applications), but
only if only one application (windowless application) component is requested to
avoid ambiguity. Changing the build script to use different toolkit is then
matter of replacing only the requested `*Application` component (and one
<tt>#</tt>`include` line in the actual code, as said above).

@code
find_package(Magnum REQUIRED GlutApplication)

include_directories(${MAGNUM_INCLUDE_DIRS} ${MAGNUM_APPLICATION_INCLUDE_DIRS})

add_executable(myapplication MyApplication.cpp)
target_link_libraries(myapplication
    ${MAGNUM_LIBRARIES}
    ${MAGNUM_APPLICATION_LIBRARIES})
@endcode

@section platform-configuration Specifying configuration

By default the application is created with some reasonable defaults (e.g.
window size 800x600 pixels). If you want something else, you can pass
@ref GlutApplication::Configuration "Configuration" instance to application
constructor. Using method chaining it can be done conveniently like this:
@code
MyApplication::MyApplication(int& argc, char** argv):
    Platform::Application(argc, argv, Configuration()
        .setTitle("My Application")
        .setSize({800, 600}))
{
    // ...
}
@endcode

However, sometimes you would need to configure the application based on some
configuration file or system introspection. In that case you can pass `nullptr`
instead of @ref GlutApplication::Configuration "Configuration" instance and
then specify it later with @ref GlutApplication::createContext() "createContext()":
@code
MyApplication::MyApplication(int& argc, char** argv): Platform::Application(argc, argv, nullptr) {
    // ...

    createContext(Configuration()
        .setTitle("My Application")
        .setSize(size));

    // ...
}
@endcode

If the context creation in constructor or @ref GlutApplication::createContext() "createContext()"
fails, the application exits. However, it is also possible to negotiate the
context using @ref GlutApplication::tryCreateContext() "tryCreateContext()".
The only difference is that this function returns `false` instead of exiting.
You can for example try enabling MSAA and if the context creation fails, fall
back to no-AA rendering:
@code
MyApplication::MyApplication(int& argc, char** argv): Platform::Application(argc, argv, nullptr) {
    // ...

    Configuration conf;
    conf.setTitle("My Application")
        .setSampleCount(16);

    if(!tryCreateContext(conf))
        createContext(conf.setSampleCount(0));

    // ...
}
@endcode

@section platform-custom Using custom platform toolkits

In case you want to use some not-yet-supported toolkit or you don't want to use
the wrappers in @ref Platform namespace, you can initialize %Magnum manually.
All you need is to create OpenGL context and then create instance of
@ref Context class, which will take care of proper initialization and feature
detection. The instance must be alive for whole application lifetime. Example
`main()` function with manual initialization:
@code
int main(int argc, char** argv) {
    // Create OpenGL context ...

    {
        // Initialize Magnum
        Context context;

        // open window, enter main loop...

        // Magnum context gets destroyed
    }

    // delete OpenGL context ...

    return 0;
}
@endcode

-   Next page: @ref types
*/
}}