Tutorial 18: Splitscreen

A tutorial by Max Winkel.

In this tutorial we'll learn how to use splitscreen (e.g. for racing-games) with Irrlicht. We'll create a viewport divided into 4 parts, with 3 fixed cameras and one user-controlled.

Ok, let's start with the headers (I think there's nothing to say about it)

#include <irrlicht.h>
#include "driverChoice.h"
#ifdef _MSC_VER
#pragma comment(lib, "Irrlicht.lib")
#endif
//Namespaces for the engine
using namespace irr;
using namespace core;
using namespace video;
using namespace scene;

Now we'll define the resolution in a constant for use in initializing the device and setting up the viewport. In addition we set up a global variable saying splitscreen is active or not.

//Resolution
const int ResX=800;
const int ResY=600;
const bool fullScreen=false;
//Use SplitScreen?
bool SplitScreen=true;

Now we need four pointers to our cameras which are created later:

//cameras
ICameraSceneNode *camera[4]={0,0,0,0};

In our event-receiver we switch the SplitScreen-variable, whenever the user press the S-key. All other events are sent to the FPS camera.

class MyEventReceiver : public IEventReceiver
{
public:
virtual bool OnEvent(const SEvent& event)
{
//Key S enables/disables SplitScreen
if (event.EventType == irr::EET_KEY_INPUT_EVENT &&
event.KeyInput.Key == KEY_KEY_S && event.KeyInput.PressedDown)
{
SplitScreen = !SplitScreen;
return true;
}
//Send all other events to camera4
if (camera[3])
return camera[3]->OnEvent(event);
return false;
}
};

Ok, now the main-function: First, we initialize the device, get the SourceManager and VideoDriver, load an animated mesh from .md2 and a map from .pk3. Because that's old stuff, I won't explain every step. Just take care of the maps position.

int main()
{
// ask user for driver
video::E_DRIVER_TYPE driverType=driverChoiceConsole();
if (driverType==video::EDT_COUNT)
return 1;
//Instance of the EventReceiver
MyEventReceiver receiver;
//Initialise the engine
IrrlichtDevice *device = createDevice(driverType,
dimension2du(ResX,ResY), 32, fullScreen,
false, false, &receiver);
if (!device)
return 1;
ISceneManager *smgr = device->getSceneManager();
IVideoDriver *driver = device->getVideoDriver();
//Load model
IAnimatedMesh *model = smgr->getMesh("../../media/sydney.md2");
if (!model)
return 1;
IAnimatedMeshSceneNode *model_node = smgr->addAnimatedMeshSceneNode(model);
//Load texture
if (model_node)
{
ITexture *texture = driver->getTexture("../../media/sydney.bmp");
model_node->setMaterialTexture(0,texture);
model_node->setMD2Animation(scene::EMAT_RUN);
//Disable lighting (we've got no light)
model_node->setMaterialFlag(EMF_LIGHTING,false);
}
//Load map
device->getFileSystem()->addFileArchive("../../media/map-20kdm2.pk3");
IAnimatedMesh *map = smgr->getMesh("20kdm2.bsp");
if (map)
{
ISceneNode *map_node = smgr->addOctreeSceneNode(map->getMesh(0));
//Set position
map_node->setPosition(vector3df(-850,-220,-850));
}

Now we create our four cameras. One is looking at the model from the front, one from the top and one from the side. In addition there's a FPS-camera which can be controlled by the user.

// Create 3 fixed and one user-controlled cameras
//Front
camera[0] = smgr->addCameraSceneNode(0, vector3df(50,0,0), vector3df(0,0,0));
//Top
camera[1] = smgr->addCameraSceneNode(0, vector3df(0,50,0), vector3df(0,0,0));
//Left
camera[2] = smgr->addCameraSceneNode(0, vector3df(0,0,50), vector3df(0,0,0));
//User-controlled
camera[3] = smgr->addCameraSceneNodeFPS();
// don't start at sydney's position
if (camera[3])
camera[3]->setPosition(core::vector3df(-50,0,-50));

Create a variable for counting the fps and hide the mouse:

//Hide mouse
device->getCursorControl()->setVisible(false);
//We want to count the fps
int lastFPS = -1;

There wasn't much new stuff - till now! Only by defining four cameras, the game won't be splitscreen. To do this you need several steps:

- Set the viewport to the whole screen
- Begin a new scene (Clear screen)
- The following 3 steps are repeated for every viewport in the splitscreen
  - Set the viewport to the area you wish
  - Activate the camera which should be "linked" with the viewport
  - Render all objects
- If you have a GUI:
  - Set the viewport the whole screen
  - Display the GUI
- End scene

Sounds a little complicated, but you'll see it isn't:

while(device->run())
{
//Set the viewpoint to the whole screen and begin scene
driver->setViewPort(rect<s32>(0,0,ResX,ResY));
driver->beginScene(true,true,SColor(255,100,100,100));
//If SplitScreen is used
if (SplitScreen)
{
//Activate camera1
smgr->setActiveCamera(camera[0]);
//Set viewpoint to the first quarter (left top)
driver->setViewPort(rect<s32>(0,0,ResX/2,ResY/2));
//Draw scene
smgr->drawAll();
//Activate camera2
smgr->setActiveCamera(camera[1]);
//Set viewpoint to the second quarter (right top)
driver->setViewPort(rect<s32>(ResX/2,0,ResX,ResY/2));
//Draw scene
smgr->drawAll();
//Activate camera3
smgr->setActiveCamera(camera[2]);
//Set viewpoint to the third quarter (left bottom)
driver->setViewPort(rect<s32>(0,ResY/2,ResX/2,ResY));
//Draw scene
smgr->drawAll();
//Set viewport the last quarter (right bottom)
driver->setViewPort(rect<s32>(ResX/2,ResY/2,ResX,ResY));
}
//Activate camera4
smgr->setActiveCamera(camera[3]);
//Draw scene
smgr->drawAll();
driver->endScene();

As you can probably see, the image is rendered for every viewport separately. That means, that you'll loose much performance. Ok, if you're asking "How do I have to set the viewport to get this or that screen?", don't panic. It's really easy: In the rect-function you define 4 coordinates:

- X-coordinate of the corner left top
- Y-coordinate of the corner left top
- X-coordinate of the corner right bottom
- Y-coordinate of the corner right bottom

That means, if you want to split the screen into 2 viewports you would give the following coordinates:

- 1st viewport: 0,0,ResX/2,ResY
- 2nd viewport: ResX/2,0,ResX,ResY

If you didn't fully understand, just play around with the example to check out what happens.

Now we just view the current fps and shut down the engine, when the user wants to:

//Get and show fps
if (driver->getFPS() != lastFPS)
{
lastFPS = driver->getFPS();
core::stringw tmp = L"Irrlicht SplitScreen-Example (FPS: ";
tmp += lastFPS;
tmp += ")";
device->setWindowCaption(tmp.c_str());
}
}
//Delete device
device->drop();
return 0;
}

That's it! Just compile and play around with the program. Note: With the S-Key you can switch between using splitscreen and not.