Tutorial - Stereo rendering
In this tutorial I will describe how to perform quadbuffered stereo rendering with Horde3D. This explicitly requires a graphics card that supports quad-buffering, i.e. rendering to two different output devices(Nvidia Quadro or ATI/AMD FireGL). This has been tested with a stereo projection system and polarization glasses.
To do this we need to render our scene from two different points of view(left and right eye) and send each frame to the corresponding output device.
Stereoscopic Geometry in OpenGL In this tutorial we will only use an asymmetric frustum.
Enable quadbuffering
First of all we need to tell our graphics card to enable quadbuffering if available. The following code shows how to do this using SDL. We will try to enable stereo rendering by default but it will fall back to non-stereo if the graphics card does not have quadbuffering capabilities. We will enable stereo rendering only in fullscreen mode.
| SDL Stereo Setup (main.cpp) |
bool setupWindow( int width, int height, bool fullscreen )
{
const SDL_VideoInfo* videoInfo = SDL_GetVideoInfo();
SDL_Surface* surface;
appWidth = fullscreen ? videoInfo->current_w : width;
appHeight = fullscreen ? videoInfo->current_h : height;
if(fullscreen)
{
// enable stereo if possible (only in fullscreen mode)
if ( SDL_GL_SetAttribute(SDL_GL_STEREO, 1) == 0) {
std::cout<<"Stereo flag set!"<<std::endl;
}
// Try to initialize the SDL_Surface with Stereo enabled
if (!(surface = SDL_SetVideoMode(appWidth,appHeight,32,SDL_OPENGL | SDL_FULLSCREEN | SDL_HWSURFACE)))
{
// if initialization with stereo enabled failed disable the stereo flag and retry
std::cerr << "STEREO initialization failed! Restarting..."<< std::endl;
SDL_GL_SetAttribute(SDL_GL_STEREO, 0);
if (!(surface = SDL_SetVideoMode(appWidth, appHeight, 32, SDL_OPENGL | SDL_FULLSCREEN | SDL_HWSURFACE))) {
std::cerr << "SDL_SetVideoMode failed: " << SDL_GetError() << std::endl;
SDL_Quit();
return 0;
}
}
}else // windowed
{
if (!(surface = SDL_SetVideoMode(appWidth,appHeight,32,SDL_OPENGL | SDL_HWSURFACE)))
{
std::cerr << "SDL_SetVideoMode failed: " << SDL_GetError() << std::endl;
SDL_Quit();
return 0;
}
SDL_WM_SetCaption("SDL App",NULL);
}
// check if stereo rendering is enabled
int ga = 0;
if (SDL_GL_GetAttribute(SDL_GL_STEREO, &ga) == 0) {
if (ga == 0)
std::cout<<"No stereo rendering available."<<std::endl;
else
std::cout<<"Stereo rendering enabled!."<<std::endl;
}
return true;
} |
This will also work with GLFW. Just call this line before opening your GLFW window.
| GLFW stereo flag |
glfwOpenWindowHint( GLFW_STEREO, GL_TRUE ); |
Render the scene
Now we need to calculate the eye offset and render the scene twice (once for each eye). This is done by switching the Horde3D render buffer to the corresponding eye, moving the camera to the desired eye offset and render the scene to the specified buffer. Again, this will only be done if stereo rendering has been enabled successfully.
We will calculate the eye offset by simply "strafing" the camera from its original position slightly to the left and right and rotating it inwards. This example has some keys assigned to adjust the eye offset and strabismus ("cross-eyedness") on the fly. In normal (non-stereo) mode we can switch between the eyes to check the camera position even if stereo rendering is not available.
| Render the scene (app.cpp) |
float eyOffsetFactor = 3.0f;
float strabismus = 3.0f;
int eye = 0;
void Application::mainLoop( int fps )
{
_curFPS = fps;
keyHandler();
if(! _freeze )
{
// calculate eye-offsets for stereo rendering
float xEyeOffset = eyOffsetFactor*sinf( degToRad( _ry + 90 ) );
float zEyeOffset = eyOffsetFactor*cosf( degToRad( _ry + 90 ) );
// ........
// Render scene
// render stereo
int ga = 0;
if (SDL_GL_GetAttribute(SDL_GL_STEREO, &ga) == 0 && ga == 1) {
Horde3D::setNodeParami(_cam, CameraNodeParams::OutputBufferIndex, 0);
Horde3D::setNodeTransform( _cam, _x-xEyeOffset, _y, _z-zEyeOffset, _rx ,_ry-strabismus, 0, 1, 1, 1 );
Horde3D::render( _cam );
Horde3D::setNodeParami(_cam, CameraNodeParams::OutputBufferIndex, 1);
Horde3D::setNodeTransform( _cam, _x+xEyeOffset, _y, _z+zEyeOffset, _rx ,_ry+strabismus, 0, 1, 1, 1 );
Horde3D::render( _cam );
}
else { // non stereo
// Set camera parameters
if (eye == 1) // left eye
Horde3D::setNodeTransform( _cam, _x-xEyeOffset, _y, _z-zEyeOffset, _rx ,_ry-strabismus, 0, 1, 1, 1 );
else if (eye == 2) // right eye
Horde3D::setNodeTransform( _cam, _x+xEyeOffset, _y, _z+zEyeOffset, _rx ,_ry+strabismus, 0, 1, 1, 1 );
else if(eye == 0) // normal camera (centered)
Horde3D::setNodeTransform( _cam, _x, _y, _z, _rx ,_ry, 0, 1, 1, 1 );
Horde3D::render( _cam );
}
// Remove all overlays
Horde3D::clearOverlays();
// Write all mesages to log file
Horde3DUtils::dumpMessages();
Horde3D::finalizeFrame(); // comment this line if you are using Horde3D 1.0.0 beta 2
SDL_GL_SwapBuffers();
}
}
void Application::keyPressEvent( SDLKey key )
{
// add more key events here...
// switch between eyes (0: normal/center, 1: left eye, 2: right eye)
if( key == SDLK_F5 ) {// F5
++eye;
if (eye >= 3)
eye = 0;
std::cout<<"eye: "<<eye<<std::endl;
}
}
void Application::keyHandler()
{
// add more keys if desired...
// adjust strabismus (cross eyedness)
if(_keys[SDLK_0])
{
if (strabismus < 45)
strabismus += 0.3f;
}
if(_keys[SDLK_9])
{
if (strabismus > 0)
strabismus -= 0.3f;
}
// adjust eye offset
if(_keys[SDLK_8])
{
eyeOffset += 0.3f;
}
if(_keys[SDLK_7])
{
if (eyeOffset > 0) {
eyeOffset -= 0.3f;
}
}
} |
TODO
- calculate symmetric frustum
- add a second camera node for easier camera movement
