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4. Let There Be Light > Creating weather controls
When building Ogre applications that simulate an outdoor environment, we often need to control weather conditions. In this recipe, we'll build an application with controls that change the parameters of a particle system to simulate different rain-like conditions. We'll also use sound in our application to enhance the rain effect.
Add the sounds folder, which contains nature sounds, such as rain and thunder, in your media folder.
To follow along with this recipe, open the solution located in the Recipes/Chapter04 folder in the code bundle available on the Packt website.
- First, create a new Ogre MFC application named
WeatherConditions, by following the Creating an MFC Ogre application recipe, in Chapter 1, - Next, create a SAPI voice.
m_cpVoice.CoCreateInstance(CLSID_SpVoice);
- Create a submenu named Weather Control in the main menu. Then, add commands: Rain, Snow, Fog, Sky, and Sun to the submenu. For this recipe, we will only be implementing the rain functionality, but it will be easy to complete the other controls, once you see how the rain is implemented.
- Next, add an event handler to the Rain submenu item using the Event Handler Wizard.
void CWeatherControlView::OnWeatherControlRain() { Ogre::SceneNode *RainNode = NULL; if (!m_SceneManager->hasParticleSystem("Rain")) { m_Rain = m_SceneManager->createParticleSystem("Rain", "Examples/Rain"); if (m_Rain != NULL) { RainNode = m_SceneManager-> getRootSceneNode()->createChildSceneNode("RainNode"); RainNode->attachObject(m_Rain); m_Rain->setVisible(false); } } if (m_RainControlDlg == NULL) { m_RainControlDlg = new CRainControlDlg(); m_RainControlDlg->Create(IDD_RAIN_CONTROL); } m_RainControlDlg->ShowWindow(SW_SHOW); } - In the Rain submenu event handler, we create the rain particle system and the Rain Control dialog-box, and then show it.
- Create the Rain Control dialog-box using the Dialog Editor.
Using this dialog-box, we can start and stop the rain, control particle dimensions, and enable or disable rain sounds.
- Now that we've created the dialog-box, we need to add the event handler code for the dialog-box controls. Add a message handler to the Rain Control dialog-box called
OnHScrollthat handles theWM_HSCROLLmessage. TheWM_HSCROLLmessage is sent when a click is detected in a horizontal scroll bar. Inside theOnHScroll, we simply check the position of the particle width and height controls, and modify the particle system with the updated values.void CRainControlDlg::OnHScroll(UINT nSBCode, UINT nPos, CScrollBar* pScrollBar) { CMainFrame *MainFrame = (CMainFrame *)(( CWeatherControlApp*)AfxGetApp())->GetMainWnd(); CWeatherControlView *View = (CWeatherControlView *)MainFrame->GetActiveView(); int ParticleWidth = m_ParticleWidth.GetPos(); int ParticleHeight = m_ParticleHeight.GetPos(); View->m_Rain->setDefaultDimensions(ParticleWidth, ParticleHeight); CDialogEx::OnHScroll(nSBCode, nPos, pScrollBar); } - Next, add an event handler named
OnClickActionto the Start/Stop button to handle the click event. InsideOnClickAction, we toggle the rain visibility and rain sounds.View->m_Rain->setVisible(!View->m_Rain->getVisible()); if (View->m_Rain->getVisible()) { m_Action.SetWindowTextA("Stop"); View->SetTimer(ID_RAIN_TIMER, 1, 0); } else { m_Action.SetWindowTextA("Start"); View->KillTimer(ID_RAIN_TIMER); WeatherControlApp->m_cpVoice->Pause(); }We also start or stop the
ID_RAIN_TIMERto toggle rain sounds in ourOnTimer()function that gets called every time we receive a timer message. - To handle the timer messages, add an
ON_WM_TIMERmessage handler toCWeatherControlView, and name itOnTimer. In theOnTimermember function, we will play rain sounds and render the scene when we receive theID_RAIN_TIMERtimer event.SoundPath += L"\\..\\..\\media\\sounds\\rain\\rain storm.wav"; CWeatherControlApp* WeatherControlApp = (CWeatherControlApp*)AfxGetApp(); CComPtr<ISpVoice> Voice = WeatherControlApp->m_cpVoice; CComPtr<ISpStream> cpWavStream; switch (nIDEvent) { case ID_RAIN_TIMER: if (m_RainControlDlg != NULL){ if (m_RainControlDlg->m_PlaySound && m_Rain->getVisible()) { SPBindToFile(SoundPath, SPFM_OPEN_READONLY, &cpWavStream); Voice->Resume(); Voice->SpeakStream(cpWavStream, SPF_ASYNC, NULL); } else { Voice->Pause(); } } Root->renderOneFrame();The
SPBindToFilefunction binds the audio stream to the specified file, andSpeakStreamplays the contents of the stream. In our case, when we receive anID_RAIN_TIMERevent, we play the rain sound.
The settings for our Examples/Rain particle system reside in the media/particle/Examples.particle file. The .particle file is just a text file and the settings are detailed in the Ogre online manual:
particle_system Examples/Rain
{
material Examples/Droplet
particle_width 20
particle_height 100
cull_each true
quota 10000
// Make common direction straight down (faster than self oriented)
billboard_type oriented_common
common_direction 0 -1 0
// Area emitter
emitter Box
{
angle 0
emission_rate 100
time_to_live 5
direction 0 -1 0
velocity 50
width 1000
height 1000
depth 0
}
// Gravity
affector LinearForce
{
force_vector 0 -200 0
force_application add
}
}
The rain particle effect uses a box emitter, so all the particles originate from a flat 1000x1000 box. Note that we use the Y-axis as the up and down axis in our example, and our material is the Examples/Droplet material found in the media/materials/scripts/Examples.material file.
material Examples/Droplet{
technique {
pass {
emissive 0.3 0.3 0.3
scene_blend colour_blend
depth_write off
diffuse vertexcolour
texture_unit {
texture basic_droplet.png
}
}
}
}
When you run the program and turn on the rain effect, you can see the rain particles falling on our robot overlord.
