MadMarx Tutorial 9 - Part 3         Render A Texture To Itself Using A Temporary Texture
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Foreword.

If you prefer tutorials that come with a framework => check the other wiki tutorial series.
If you prefer tutorials that go step by step without a framework => this page should be ok.

I assume you know C++. If not, this tutorial will probably be hard to understand !

This tutorial presents only a few elements of Ogre3D.

You can download the code and media for this tutorial at the bottom of this wiki page.
This little tutorial is an extract of a bigger project which contains more tutorials & helper classes.
This bigger project is avaible there :
https://sourceforge.net/projects/so3dtools/(external link)

Also, make sure you read these tutorials in order!

Tutorial Description

This program is mainly the same as the previous RenderToTexture tutorial,
but this time I use 'FBO' (frame buffer object).
To be able to use 'FBO' kind of render to texture, I am not allowed to
make a texture render to itself (on my graphic card at least...).
As a consequence : I create here an intermediate texture, that will receive the result
of the render to texture. So, in this program we see how to copy content from one texture
to another texture, directly on the GPU.

Conclusion : don't trust too much your graphic card's pilot.

During GL render system configuration, before root initialisation

 

¤					lRenderSystem->setConfigOption("RTT Preferred Mode","FBO");

After viewport creation & resource loading

Now I create a special texture. This texture allows to do what is called a
'render to texture'. Which means that you can render your scene into
it, and then use this texture as any other in a material.
In order to keep a good framerate, I set its number of mipmaps to 0.

¤	Ogre::TextureManager& lTextureManager = Ogre::TextureManager::getSingleton();
	Ogre::String lTextureName = "MyFirstRtt";
	bool lGammaCorrection = false;
	unsigned int lAntiAliasing = 0;
	unsigned int lNumMipmaps = 0;
	Ogre::TexturePtr lTextureWithRtt = lTextureManager.createManual(lTextureName, lNameOfResourceGroup, 
		Ogre::TEX_TYPE_2D, 512, 512, lNumMipmaps,
		Ogre::PF_R8G8B8, Ogre::TU_RENDERTARGET, 0, lGammaCorrection, lAntiAliasing);

I create an intermediate texture, that will receive a copy of the rtt texture.
Since I will dynamically write in this texture, I have chosen the texture usage Ogre::TU_DYNAMIC_WRITE_ONLY.
There are very detailed informations on texture usage & hardware buffers in the ogre3D manual.

¤	Ogre::String lIntermediateTextureName = "IntermediateTexture";
	Ogre::TexturePtr lIntermediateTexture = lTextureManager.createManual(lIntermediateTextureName, lNameOfResourceGroup, 
		Ogre::TEX_TYPE_2D, 512, 512, lNumMipmaps,
		Ogre::PF_R8G8B8, Ogre::TU_DYNAMIC_WRITE_ONLY, 0, lGammaCorrection, lAntiAliasing);

now I will link this texture to a camera, by creating a viewport in the texture.

¤	Ogre::RenderTexture* lRenderTarget = NULL;
	{
		Ogre::HardwarePixelBufferSharedPtr lRttBuffer = lTextureWithRtt->getBuffer();
		lRenderTarget = lRttBuffer->getRenderTarget();
		lRenderTarget->setAutoUpdated(false);

I create a camera so that it has a beautiful '1' aspect ratio.

¤		Ogre::Camera * lRttCamera = lScene->createCamera("RttCamera");
		lRttCamera->setNearClipDistance(1.5f);
		lRttCamera->setFarClipDistance(3000.0f); 
		lRttCamera->setAspectRatio(1.0f);

I attach this camera to the same node than main camera.

¤		lCameraNode->attachObject(lRttCamera);

In the texture I will draw first a Big Blue Viewport.

¤		Ogre::Viewport* lRttViewport1 = lRenderTarget->addViewport(lRttCamera, 50, 0.00f, 0.00f, 1.0f, 1.0f);
		lRttViewport1->setAutoUpdated(true);
		Ogre::ColourValue lBgColor1(1.0,0.0,0.0,1.0);
		lRttViewport1->setBackgroundColour(lBgColor1);

In the texture I will draw then a more little red Viewport.
The previous viewport with the ZOrder at 50 will be drawn first (50 < 100).

¤		Ogre::Viewport* lRttViewport2 = lRenderTarget->addViewport(lRttCamera, 100, 0.05f, 0.05f, 0.9f, 0.9f);
		lRttViewport2->setAutoUpdated(true);
		Ogre::ColourValue lBgColor2(0.0,0.0,1.0,1.0);
		lRttViewport2->setBackgroundColour(lBgColor2);
	}

This material will use the intermediate texture.

¤	Ogre::String lMaterialName = "MyRttMaterial";
	{

I get a reference on the material manager, which is a singleton.

¤		Ogre::MaterialManager& lMaterialManager = Ogre::MaterialManager::getSingleton();
		Ogre::MaterialPtr lMaterial = lMaterialManager.create(lMaterialName, lNameOfResourceGroup);
		Ogre::Technique * lTechnique = lMaterial->getTechnique(0);
		Ogre::Pass* lPass = lTechnique->getPass(0);
		Ogre::TextureUnitState* lTextureUnit = lPass->createTextureUnitState();
		lTextureUnit->setTextureName(lIntermediateTextureName);

I use no mipmap, and I just use some bilinear filtering on the result.

¤		lTextureUnit->setNumMipmaps(0);
		lTextureUnit->setTextureFiltering(Ogre::TFO_BILINEAR);

I make the texture rotate.
The material can handle 'special effects' on the texture coordinates.
Here I rotate the texture coordinates.

¤		float lRotateSpeed = 0.01f;
		lTextureUnit->setRotateAnimation(lRotateSpeed);

Entity creation

Now I will create the corresponding entity, and its scenenode.

¤	{
		Ogre::Entity* lEntity = lScene->createEntity(lNameOfTheMesh);
		lEntity->setMaterialName(lMaterialName);

Now I attach it to a scenenode, so that it becomes present in the scene.

¤		Ogre::SceneNode* lNodeWithEntity = lNodeWithEntity = lRootSceneNode->createChildSceneNode();
		lNodeWithEntity->attachObject(lEntity);

I move the SceneNode so that it is visible to the camera.

¤		lNodeWithEntity->setPosition(0.0f, 0.0f, -1.8f);
	}

Full while() loop

 

¤	while(!lOgreInit.mWindow->isClosed())
	{

Drawings

First I update the rendertarget, and then I make the copy of its content.
I show 2 versions of the copying.

¤		lRenderTarget->update();
		int lCopyingVersion = 1;
		if(0 == lCopyingVersion)
		{

this version resizes the texture if needed.

¤			lTextureWithRtt->copyToTexture(lIntermediateTexture);
		}else if(1 == lCopyingVersion)
		{

This version crop a part of the image to the other part.
Since I use the texture same size there is no problem.
The HardwarePixelBuffer is a pixel buffer, there is at least one per texture.
I will copy the content from the RTT-buffer to the intermediate texture-buffer.

¤			Ogre::HardwarePixelBufferSharedPtr lBufferRtt = lTextureWithRtt->getBuffer(0,0);
			Ogre::HardwarePixelBufferSharedPtr lBufferIntermediate = lIntermediateTexture->getBuffer(0,0);
			size_t left = 0;
			size_t top = 0;
			size_t right = 511;
			size_t bottom = 511;
			Ogre::Image::Box lSourceBox(left, top, right, bottom);
			Ogre::Image::Box lDestinationBox(left, top, right, bottom);
 
			lBufferIntermediate->blit(lBufferRtt, lSourceBox, lDestinationBox);
		}

the window update its content.
each viewport that is 'autoupdated' will be redrawn now,
in order given by its z-order.

¤		lWindow->update(false);

The drawn surface is then shown on the screen
(google "double buffering" if you want more details).
I always use vertical synchro.

¤		bool lVerticalSynchro = true;
		lWindow->swapBuffers(lVerticalSynchro);

This update some internal counters and listeners.
Each render surface (window/rtt/mrt) that is 'auto-updated' has got its 'update' function called.

¤		lRoot->renderOneFrame();
 
		Ogre::WindowEventUtilities::messagePump();
	}

 

main.cpp , main.cs

// This program is mainly the same as the previous RenderToTexture tutorial,
// but this time I use 'FBO' (frame buffer object).
// To be able to use 'FBO' kind of render to texture, I am not allowed to 
// make a texture render to itself (on my graphic card at least...).
// As a consequence : I create here an intermediate texture, that will receive the result
// of the render to texture. So, in this program we see how to copy content from one texture 
// to another texture, directly on the GPU.
//
// Conclusion : don't trust too much your graphic card's pilot.
 
// I will use std::auto_ptr so I need to include 'memory'. 
// If you don't know std::auto_ptr, you should check some C++ tutorials/lesson on this matter.
#include <memory>
// I will check for std::exception. If you don't know what exception/try/catch means, you should learn C++ first.
#include <exception>
 
// These are some files that we need to include to use Ogre3D. Note that you can at the beginnings use directly "Ogre.h", to include lots of commonly used classes.
#include "OGRE/OgreRoot.h"
#include "OGRE/OgreRenderSystem.h"
#include "OGRE/OgreRenderWindow.h"
#include "OGRE/OgreWindowEventUtilities.h"
#include "OGRE/OgreManualObject.h"
#include "OGRE/OgreEntity.h"
#include "OGRE/OgreMaterialManager.h"
#include "OGRE/OgreHardwarePixelBuffer.h"
 
//Here I include my other files, like the one for SimpleOgreInit...
#include "SimpleOgreInit.h"
 
#include "EasyDefines.h"
 
// I declare a function in which I will make my whole application.
// This is easy then to add more things later in that function.
// The main will call this function and take care of the global try/catch.
void AnOgreApplication()
{
	// I construct my object that will allow me to initialise Ogre easily.
	OgreEasy::SimpleOgreInit lOgreInit;
 
	if(!lOgreInit.initOgre())
	{
		std::cout<<"Impossible to init Ogre correctly."<<std::endl;
		return;
	}
 
	//I prefer to be able to access my variables directly.
	Ogre::Root* lRoot = lOgreInit.mRoot.get();
	Ogre::RenderWindow* lWindow = lOgreInit.mWindow;
 
	// I create a scenemanager. This is like a 'Scene', in which I can put lights, 3d objects, etc...
	// The scenemanager contains an arborescent graph of 'SceneNodes'. To manage elements of the scene,
	// I will create SceneNodes in the SceneManager, and attach the elements to the scenenodes.
	// First parameter : I select a kind of SceneManager. This may have a huge impact on performance.
	// Depending on your scene, some are better than other. The default one does no optimization at all.
	// Second parameter : I give a name to the scenemanager.
	// Note : It is easy to have more than one scenemanager (If you got 2 different scenes for example).
	Ogre::SceneManager* lScene = lRoot->createSceneManager(Ogre::ST_GENERIC, "MyFirstSceneManager");
 
	// The 'root SceneNode' is the only scenenode at the beginning in the SceneManager.
	// The SceneNodes can be seen as 'transformation' containers <=> it contains scale/position/rotation
	// of the objects. There is only 1 root scenenode, and all other scenenode are 
	// its direct or indirect children.
	Ogre::SceneNode* lRootSceneNode = lScene->getRootSceneNode();
 
	// I create a camera. It represent a 'point of view' in the scene.
	Ogre::Camera* lCamera = lScene->createCamera("MyFirstCamera");
 
	// I attach the camera to a new SceneNode. It will be easier then to move it in the scene.
	Ogre::SceneNode* lCameraNode = lRootSceneNode->createChildSceneNode("MyFirstCameraNode");
	lCameraNode->attachObject(lCamera);
 
	// We create a viewport on a part of the window.
	// A viewport is the link between 1 camera and 1 drawing surface (here the window).
	// I can then call 'update();' on it to make it draw the Scene from the camera.
	// You can have several viewports on 1 window.
	// Check API for details on parameters.
	unsigned short lMainViewportZOrder = 100;
	Ogre::Viewport * vp = lWindow->addViewport(lCamera, lMainViewportZOrder);
 
	// I want the viewport to draw the scene automatically
	// when I will call lWindow->update();
	vp->setAutoUpdated(true);
 
	// I choose a color for this viewport. 
	// I prefer to have a bright color, to detect holes in geometry etc...
	vp->setBackgroundColour(Ogre::ColourValue(1,0,1));
 
	// I choose the visual ratio of the camera. To make it looks real, I want it the same as the viewport.
	float ratio = float(vp->getActualWidth()) / float(vp->getActualHeight());
	lCamera->setAspectRatio(ratio);
 
	// I choose the clipping far& near planes. if far/near>2000, you can get z buffer problem.
	// eg : far/near = 10000/5 = 2000 . it's ok.
	// If (far/near)>2000 then you will likely get 'z fighting' issues.
	lCamera->setNearClipDistance(1.5f);
	lCamera->setFarClipDistance(3000.0f); 
 
	// I want my window to be active
	lWindow->setActive(true);
 
	// I want to update myself the content of the window, not automatically.
	lWindow->setAutoUpdated(false);
 
	// Here I choose a name for a resource group. Then I create it.
	// Often, a resourcegroup is a good way to store the data corresponding
	// to a level in a game.
	Ogre::String lNameOfResourceGroup = "Mission 1 : Deliver Tom";
	{
		Ogre::ResourceGroupManager& lRgMgr = Ogre::ResourceGroupManager::getSingleton();
		lRgMgr.createResourceGroup(lNameOfResourceGroup);
 
		// The function 'initialiseResourceGroup' parses scripts if any in the locations.
		lRgMgr.initialiseResourceGroup(lNameOfResourceGroup);
 
		// Files that can be loaded are loaded.
		lRgMgr.loadResourceGroup(lNameOfResourceGroup);
	}
 
	// Now I create a special texture. This texture allows to do what is called a 
	// 'render to texture'. Which means that you can render your scene into 
	// it, and then use this texture as any other in a material.
	// In order to keep a good framerate, I set its number of mipmaps to 0.
	Ogre::TextureManager& lTextureManager = Ogre::TextureManager::getSingleton();
	Ogre::String lTextureName = "MyFirstRtt";
	bool lGammaCorrection = false;
	unsigned int lAntiAliasing = 0;
	unsigned int lNumMipmaps = 0;
	Ogre::TexturePtr lTextureWithRtt = lTextureManager.createManual(lTextureName, lNameOfResourceGroup, 
		Ogre::TEX_TYPE_2D, 512, 512, lNumMipmaps,
		Ogre::PF_R8G8B8, Ogre::TU_RENDERTARGET, 0, lGammaCorrection, lAntiAliasing);
 
	// I create an intermediate texture, that will receive a copy of the rtt texture.
	// Since I will dynamically write in this texture, I have chosen the texture usage Ogre::TU_DYNAMIC_WRITE_ONLY.
	// There are very detailed informations on texture usage & hardware buffers in the ogre3D manual.
	Ogre::String lIntermediateTextureName = "IntermediateTexture";
	Ogre::TexturePtr lIntermediateTexture = lTextureManager.createManual(lIntermediateTextureName, lNameOfResourceGroup, 
		Ogre::TEX_TYPE_2D, 512, 512, lNumMipmaps,
		Ogre::PF_R8G8B8, Ogre::TU_DYNAMIC_WRITE_ONLY, 0, lGammaCorrection, lAntiAliasing);
 
 
	// now I will link this texture to a camera, by creating a viewport in the texture.
	Ogre::RenderTexture* lRenderTarget = NULL;
	{
		Ogre::HardwarePixelBufferSharedPtr lRttBuffer = lTextureWithRtt->getBuffer();
		lRenderTarget = lRttBuffer->getRenderTarget();
		lRenderTarget->setAutoUpdated(false);
 
		// I create a camera so that it has a beautiful '1' aspect ratio.
		Ogre::Camera * lRttCamera = lScene->createCamera("RttCamera");
		lRttCamera->setNearClipDistance(1.5f);
		lRttCamera->setFarClipDistance(3000.0f); 
		lRttCamera->setAspectRatio(1.0f);
 
		// I attach this camera to the same node than main camera.
		lCameraNode->attachObject(lRttCamera);
 
		// In the texture I will draw first a Big Blue Viewport.
		Ogre::Viewport* lRttViewport1 = lRenderTarget->addViewport(lRttCamera, 50, 0.00f, 0.00f, 1.0f, 1.0f);
		lRttViewport1->setAutoUpdated(true);
		Ogre::ColourValue lBgColor1(1.0,0.0,0.0,1.0);
		lRttViewport1->setBackgroundColour(lBgColor1);
 
		// In the texture I will draw then a more little red Viewport.
		// The previous viewport with the ZOrder at 50 will be drawn first (50 < 100).
		Ogre::Viewport* lRttViewport2 = lRenderTarget->addViewport(lRttCamera, 100, 0.05f, 0.05f, 0.9f, 0.9f);
		lRttViewport2->setAutoUpdated(true);
		Ogre::ColourValue lBgColor2(0.0,0.0,1.0,1.0);
		lRttViewport2->setBackgroundColour(lBgColor2);
	}
 
	// This material will use the intermediate texture.
	Ogre::String lMaterialName = "MyRttMaterial";
	{
		// I get a reference on the material manager, which is a singleton.
		Ogre::MaterialManager& lMaterialManager = Ogre::MaterialManager::getSingleton();
		Ogre::MaterialPtr lMaterial = lMaterialManager.create(lMaterialName, lNameOfResourceGroup);
		Ogre::Technique * lTechnique = lMaterial->getTechnique(0);
		Ogre::Pass* lPass = lTechnique->getPass(0);
		Ogre::TextureUnitState* lTextureUnit = lPass->createTextureUnitState();
		lTextureUnit->setTextureName(lIntermediateTextureName);
		//I use no mipmap, and I just use some bilinear filtering on the result.
		lTextureUnit->setNumMipmaps(0);
		lTextureUnit->setTextureFiltering(Ogre::TFO_BILINEAR);
 
		// I make the texture rotate.
		// The material can handle 'special effects' on the texture coordinates.
		// Here I rotate the texture coordinates.
		float lRotateSpeed = 0.01f;
		lTextureUnit->setRotateAnimation(lRotateSpeed);
 
		// Uncomment the following line to see something funnier. :-D.
		//lTextureUnit->setTransformAnimation(Ogre::TextureUnitState::TT_SCALE_U, Ogre::WFT_SINE, 0.9f, 0.5f, 0.0f, 0.2f);
	}
 
	// Now I will create a manualobject quad, and convert it to a mesh...
	Ogre::String lNameOfTheMesh = "MyQuad";
	{
		Ogre::ManualObject * lManualObject = NULL;
		Ogre::String lManualObjectName = "SomeQuad";
		lManualObject = lScene->createManualObject(lManualObjectName);
 
		// Always tell if you want to update the 3D (vertex/index) later or not.
		bool lDoIWantToUpdateItLater = false;
		lManualObject->setDynamic(lDoIWantToUpdateItLater);
 
		// BaseWhiteNoLighting is the name of a material that already exist inside Ogre.
		// Ogre::RenderOperation::OT_TRIANGLE_LIST is a kind of primitive.
		float lSize = 0.7f;
		lManualObject->begin("BaseWhiteNoLighting", Ogre::RenderOperation::OT_TRIANGLE_LIST);
		{
			float cp = 1.0f * lSize ;
			float cm = -1.0f * lSize;
			float lNumberOfTiles = 1.0f;
 
			lManualObject->position(cm, cp, 0.0f);// a vertex
			lManualObject->textureCoord(0.0f, 0.0f);
 
			lManualObject->position(cp, cp, 0.0f);// a vertex
			lManualObject->textureCoord(lNumberOfTiles, 0.0f);
 
			lManualObject->position(cp, cm, 0.0f);// a vertex
			lManualObject->textureCoord(lNumberOfTiles, lNumberOfTiles);
 
			lManualObject->position(cm, cm, 0.0f);// a vertex
			lManualObject->textureCoord(0.0, lNumberOfTiles);
 
			lManualObject->triangle(2,1,0);
			lManualObject->triangle(0,3,2);
		}
		lManualObject->end();
		lManualObject->convertToMesh(lNameOfTheMesh);
		lScene->destroyManualObject(lManualObject);
	}
 
	// Now I will create the corresponding entity, and its scenenode.
	{
		Ogre::Entity* lEntity = lScene->createEntity(lNameOfTheMesh);
		lEntity->setMaterialName(lMaterialName);
		// Now I attach it to a scenenode, so that it becomes present in the scene.
		Ogre::SceneNode* lNodeWithEntity = lNodeWithEntity = lRootSceneNode->createChildSceneNode();
		lNodeWithEntity->attachObject(lEntity);
		// I move the SceneNode so that it is visible to the camera.
		lNodeWithEntity->setPosition(0.0f, 0.0f, -1.8f);
	}
 
	// cleaning of windows events managed by Ogre::WindowEventUtilities::...
	// I call it after a 'pause in window updating', in order to maintain smoothness.
	// Explanation : if you clicked 2000 times when the windows was being created, there are 
	// at least 2000 messages created by the OS to listen to. This is made to clean them.
	lRoot->clearEventTimes();
 
	// I wait until the window is closed.
	// The "message pump" thing is something you will see in most GUI application.
	// It allow the binding of messages between the application and the OS.
	// These messages are most of the time : keystroke, mouse moved, ... or window closed.
	// If I don't do this, the message are never caught, and the window won't close.
	while(!lOgreInit.mWindow->isClosed())
	{
		// Drawings
 
		// First I update the rendertarget, and then I make the copy of its content.
		// I show 2 versions of the copying.
		lRenderTarget->update();
		int lCopyingVersion = 1;
		if(0 == lCopyingVersion)
		{
			// this version resizes the texture if needed.
			lTextureWithRtt->copyToTexture(lIntermediateTexture);
		}else if(1 == lCopyingVersion)
		{
			// This version crop a part of the image to the other part.
			// Since I use the texture same size there is no problem.
			// The HardwarePixelBuffer is a pixel buffer, there is at least one per texture.
			// I will copy the content from the RTT-buffer to the intermediate texture-buffer.
			Ogre::HardwarePixelBufferSharedPtr lBufferRtt = lTextureWithRtt->getBuffer(0,0);
			Ogre::HardwarePixelBufferSharedPtr lBufferIntermediate = lIntermediateTexture->getBuffer(0,0);
			size_t left = 0;
			size_t top = 0;
			size_t right = 511;
			size_t bottom = 511;
			Ogre::Image::Box lSourceBox(left, top, right, bottom);
			Ogre::Image::Box lDestinationBox(left, top, right, bottom);
 
			lBufferIntermediate->blit(lBufferRtt, lSourceBox, lDestinationBox);
		}
 
		// the window update its content.
		// each viewport that is 'autoupdated' will be redrawn now,
		// in order given by its z-order.
		lWindow->update(false);
 
		// The drawn surface is then shown on the screen
		// (google "double buffering" if you want more details).
		// I always use vertical synchro.
		bool lVerticalSynchro = true;
		lWindow->swapBuffers(lVerticalSynchro);	
 
		// This update some internal counters and listeners.
		// Each render surface (window/rtt/mrt) that is 'auto-updated' has got its 'update' function called.
		lRoot->renderOneFrame();
 
		Ogre::WindowEventUtilities::messagePump();
	}
 
	// Let's cleanup!
	{
		lWindow->removeAllViewports();
	}
	{
		lScene->destroyAllCameras();
		lScene->destroyAllManualObjects();
		lScene->destroyAllEntities();
		lScene->destroyAllLights();
		lRootSceneNode->removeAndDestroyAllChildren();
	}
	{
		Ogre::RenderSystem* lRenderSystem = lRoot->getRenderSystem();
		lRenderSystem->destroyRenderTarget(lTextureName);
	}
	{
		Ogre::ResourceGroupManager& lRgMgr = Ogre::ResourceGroupManager::getSingleton();
		lRgMgr.destroyResourceGroup(lNameOfResourceGroup);
	}
 
	return;
}
 
int main()
{
	try
	{
		AnOgreApplication();
		std::cout<<"end of the program"<<std::endl;
	}catch(Ogre::Exception &e)
	{
		MWARNING("!!!!Ogre::Exception!!!!\n"<<e.what());
	}catch(std::exception &e)
	{
		MWARNING("!!!!std::exception!!!!\n"<<e.what());
	}
	return 0;
}

Full program sources :
http://sourceforge.net/projects/so3dtools/files/Ogre3DWiki/09_RenderToTexture2.7z/download(external link)


Contributors to this page: kr12269 points  , madmarx760 points  and jacmoe177744 points  .
Page last modified on Sunday 08 of May, 2011 08:27:12 UTC by kr12269 points .


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