Fading objects away

[tonic]

I pondered how to take a normal fully opaque object and make it transparent so that it smoothly "fades away" and disappears. Or alternatively have a transparent object and fade it away.


On the #irrlicht IRC channel I was suggested to use getMeshManipulator and adjust the vertex colors or vertex color alpha with it, and I tried different ways to work with that. It partly solves the question. However, there was a few problems:

1. Adjusting only vertex color alpha made it possible to fade the diffuse texture part of object away, but the object still keeps being visible in other way, at least if lights are enabled. Not sure if the material setup was still somehow wrong for the case, so this could be how it's "supposed" to be, though...

2. For the case that original object doesn't need to be opaque but can be additive, adjusting vertex colors themselves makes it possible to actually fade the whole object away. Not sure if the lighting can still be on even in this case (not I think, the specular or diffuse light keeps being visible). Maybe a workaround could be to make a custom scene node and set custom lighting for the node when rendering, so that light fades away at the same time?

3. If there's several scene node instances of the same mesh, the change affects ALL of the scene nodes and not just one. Naturally one might want to have many instances of same mesh but fade only selected ones away. Workaround is probably to create a clone of the mesh for each node, but that is a bit wasteful...

4. If an object has varying vertex colors and varying vertex alphas, then it's not an option to adjust the vertex colors/alphas at all in a batch like the manipulator does. Or the manipulation should be done so that the original values are remembered and manipulator allows setting new values by multiplying original values with given color and alpha.


Would it be possible to get a mesh or scene node specific "global color & transparency" for an object? - Or is there already something like this but I didn't find it?

And is the custom scene node (derived class) to get a custom lighting per object a viable technique, or do you have better suggestions to achieve same functionality? That's something I probably need, not just related fading of objects. The solution should work also without vertex/pixel shaders.

[keless]

I don't have any answers for you; I just want to put in that I'm also eager to hear the solution as I'd like to do the same thing.

[xsocom]

Any idea how to make this?

[psychophoniac]

for beginners:
if don't mind the problems up there, use this:
(taken from example 11)

Code: Select all

/*
This tutorial shows how to use one of the built in more complex materials in irrlicht:
Per pixel lighted surfaces using normal maps and parallax mapping. It will also show
how to use fog and moving particle systems. And don't panic: You dont need any
experience with shaders to use these materials in Irrlicht.

At first, we need to include all headers and do the stuff we always do, like
in nearly all other tutorials.
*/
#include <irrlicht.h>
#include <iostream>


using namespace irr;

#pragma comment(lib, "Irrlicht.lib")


/*
For this example, we need an event receiver, to make it possible for the user
to switch between the three available material types. In addition, the event
receiver will create some small GUI window which displays what material is
currently being used. There is nothing special done in this class, so maybe
you want to skip reading it.
*/
class MyEventReceiver : public IEventReceiver
{
public:

	MyEventReceiver(scene::ISceneNode* room,
		gui::IGUIEnvironment* env, video::IVideoDriver* driver)
	{
		// store pointer to room so we can change its drawing mode
		Room = room;
		Driver = driver;

		// set a nicer font
		gui::IGUISkin* skin = env->getSkin();
		gui::IGUIFont* font = env->getFont("../../media/fonthaettenschweiler.bmp");
		if (font)
			skin->setFont(font);

		// add window and listbox
		gui::IGUIWindow* window = env->addWindow(
			core::rect<s32>(460,375,630,470), false, L"Use 'E' + 'R' to change");

		ListBox = env->addListBox(
			core::rect<s32>(2,22,165,88), window);

		ListBox->addItem(L"Diffuse");
		ListBox->addItem(L"Bump mapping");
		ListBox->addItem(L"Parallax mapping");
		ListBox->setSelected(1);

		// create problem text
		ProblemText = env->addStaticText(
			L"Your hardware or this renderer is not able to use the "\
			L"needed shaders for this material. Using fall back materials.",
			core::rect<s32>(150,20,470,80));

		ProblemText->setOverrideColor(video::SColor(100,255,255,255));

		// set start material (prefer parallax mapping if available)
		video::IMaterialRenderer* renderer =
			Driver->getMaterialRenderer(video::EMT_PARALLAX_MAP_SOLID);
		if (renderer && renderer->getRenderCapability() == 0)
			ListBox->setSelected(2);

		// set the material which is selected in the listbox
		setMaterial();
	}

	bool OnEvent(const SEvent& event)
	{
		// check if user presses the key 'E' or 'R'
		if (event.EventType == irr::EET_KEY_INPUT_EVENT &&
			!event.KeyInput.PressedDown && Room && ListBox)
		{
			// change selected item in listbox

			int sel = ListBox->getSelected();
			if (event.KeyInput.Key == irr::KEY_KEY_R)
				++sel;
			else
			if (event.KeyInput.Key == irr::KEY_KEY_E)
				--sel;
			else
				return false;

			if (sel > 2) sel = 0;
			if (sel < 0) sel = 2;
			ListBox->setSelected(sel);

			// set the material which is selected in the listbox
			setMaterial();
		}

		return false;
	}

private:

	// sets the material of the room mesh the the one set in the
	// list box.
	void setMaterial()
	{
		video::E_MATERIAL_TYPE type = video::EMT_SOLID;

		// change material setting
		switch(ListBox->getSelected())
		{
		case 0: type = video::EMT_SOLID;
			break;
		case 1: type = video::EMT_NORMAL_MAP_SOLID;
			break;
		case 2: type = video::EMT_PARALLAX_MAP_SOLID;
			break;
		}

		Room->setMaterialType(type);

		/*
		We need to add a warning if the materials will not be able to be
		displayed 100% correctly. This is no problem, they will be renderered
		using fall back materials, but at least the user should know that
		it would look better on better hardware.
		We simply check if the material renderer is able to draw at full
		quality on the current hardware. The IMaterialRenderer::getRenderCapability()
		returns 0 if this is the case.
		*/
		video::IMaterialRenderer* renderer = Driver->getMaterialRenderer(type);

		// display some problem text when problem
		if (!renderer || renderer->getRenderCapability() != 0)
			ProblemText->setVisible(true);
		else
			ProblemText->setVisible(false);
	}

private:

	gui::IGUIStaticText* ProblemText;
	gui::IGUIListBox* ListBox;

	scene::ISceneNode* Room;
	video::IVideoDriver* Driver;
};


/*
Now for the real fun. We create an Irrlicht Device and start to setup the scene.
*/
int main()
{
	// let user select driver type

	video::E_DRIVER_TYPE driverType = video::EDT_OPENGL;  

	printf("Please select the driver you want for this example:\n"\
		" (a) Direct3D 9.0c\n (b) Direct3D 8.1\n (c) OpenGL 1.5\n"\
		" (d) Software Renderer\n (e) Burning's Software Renderer\n"\
		" (f) NullDevice\n (otherKey) exit\n\n");

	char i;
	std::cin >> i;

	switch(i)
	{
		case 'a': driverType = video::EDT_DIRECT3D9;break;
		case 'b': driverType = video::EDT_DIRECT3D8;break;
		case 'c': driverType = video::EDT_OPENGL;   break;
		case 'd': driverType = video::EDT_SOFTWARE; break;
		case 'e': driverType = video::EDT_BURNINGSVIDEO;break;
		case 'f': driverType = video::EDT_NULL;     break;
		default: return 0;
	}

	// create device

	IrrlichtDevice* device = createDevice(driverType, core::dimension2d<s32>(640, 480));

	if (device == 0)
		return 1; // could not create selected driver.


	/*
	Before we start with the interesting stuff, we do some simple things:
	Store pointers to the most important parts of the engine (video driver,
	scene manager, gui environment) to safe us from typing too much,
	add an irrlicht engine logo to the window and a user controlled
	first person shooter style camera. Also, we let the engine now
	that it should store all textures in 32 bit. This necessary because
	for parallax mapping, we need 32 bit textures.
	*/

	video::IVideoDriver* driver = device->getVideoDriver();
	scene::ISceneManager* smgr = device->getSceneManager();
	gui::IGUIEnvironment* env = device->getGUIEnvironment();

	driver->setTextureCreationFlag(video::ETCF_ALWAYS_32_BIT, true);

	// add irrlicht logo
	env->addImage(driver->getTexture("../../media/irrlichtlogo2.png"),
		core::position2d<s32>(10,10));

	// add camera
	scene::ICameraSceneNode* camera =
		smgr->addCameraSceneNodeFPS(0,100.0f,300.0f);
	camera->setPosition(core::vector3df(-200,200,-200));

	// disable mouse cursor
	device->getCursorControl()->setVisible(false);


	/*
	Because we want the whole scene to look a little bit scarier, we add some fog
	to it. This is done by a call to IVideoDriver::setFog(). There you can set
	various fog settings. In this example, we use pixel fog, because it will
	work well with the materials we'll use in this example.
	Please note that you will have to set the material flag EMF_FOG_ENABLE
	to 'true' in every scene node which should be affected by this fog.
	*/
	driver->setFog(video::SColor(0,138,125,81), true, 250, 1000, 0, true);

	/*
	To be able to display something interesting, we load a mesh from a .3ds file
	which is a room I modeled with anim8or. It is the same room as
	from the specialFX example. Maybe you remember from that tutorial,
	I am no good modeler at all and so I totally messed up the texture
	mapping in this model, but we can simply repair it with the
	IMeshManipulator::makePlanarTextureMapping() method.
	*/

	scene::IAnimatedMesh* roomMesh = smgr->getMesh(
		"../../media/room.3ds");
	scene::ISceneNode* room = 0;

	if (roomMesh)
	{
		smgr->getMeshManipulator()->makePlanarTextureMapping(
				roomMesh->getMesh(0), 0.003f);

		/*
		Now for the first exciting thing: If we successfully loaded the mesh
		we need to apply textures to it. Because we want this room to be
		displayed with a very cool material, we have to do a little bit more
		than just set the textures. Instead of only loading a color map as usual,
		we also load a height map which is simply a grayscale texture. From this
		height map, we create a normal map which we will set as second texture of the
		room. If you already have a normal map, you could directly set it, but I simply
		didn´t find a nice normal map for this texture.
		The normal map texture is being generated by the makeNormalMapTexture method
		of the VideoDriver. The second parameter specifies the height of the heightmap.
		If you set it to a bigger value, the map will look more rocky.
		*/

		video::ITexture* colorMap = driver->getTexture("../../media/rockwall.bmp");
		video::ITexture* normalMap = driver->getTexture("../../media/rockwall_height.bmp");

		driver->makeNormalMapTexture(normalMap, 9.0f);

		/*
		But just setting color and normal map is not everything. The material we want to
		use needs some additional informations per vertex like tangents and binormals.
		Because we are too lazy to calculate that information now, we let Irrlicht do
		this for us. That's why we call IMeshManipulator::createMeshWithTangents(). It
		creates a mesh copy with tangents and binormals from any other mesh.
		After we've done that, we simply create a standard mesh scene node with this
		mesh copy, set color and normal map and adjust some other material settings.
		Note that we set EMF_FOG_ENABLE to true to enable fog in the room.
		*/

		scene::IMesh* tangentMesh = smgr->getMeshManipulator()->createMeshWithTangents(
			roomMesh->getMesh(0));

		room = smgr->addMeshSceneNode(tangentMesh);
		room->setMaterialTexture(0, colorMap);
		room->setMaterialTexture(1, normalMap);

		room->getMaterial(0).SpecularColor.set(0,0,0,0);

		room->setMaterialFlag(video::EMF_FOG_ENABLE, true);
		room->setMaterialType(video::EMT_PARALLAX_MAP_SOLID);
		room->getMaterial(0).MaterialTypeParam = 0.035f; // adjust height for parallax effect

		// drop mesh because we created it with a create.. call.
		tangentMesh->drop();
	}

	/*
	After we've created a room shaded by per pixel lighting, we add a sphere
	into it with the same material, but we'll make it transparent. In addition,
	because the sphere looks somehow like a familiar planet, we make it rotate.
	The procedure is similar as before. The difference is that we are loading
	the mesh from an .x file which already contains a color map so we do not
	need to load it manually. But the sphere is a little bit too small for our
	needs, so we scale it by the factor 50.
	*/

	// add earth sphere

	scene::IAnimatedMesh* earthMesh = smgr->getMesh("../../media/earth.x");
	scene::IMeshSceneNode *sphere = NULL; // i moved this outside the loop because we need it in the renderloop
	if (earthMesh)
	{
		//perform various task with the mesh manipulator
		scene::IMeshManipulator *manipulator = smgr->getMeshManipulator();

		// create mesh copy with tangent informations from original earth.x mesh
		scene::IMesh* tangentSphereMesh =
			manipulator->createMeshWithTangents(earthMesh->getMesh(0));

		// set the alpha value of all vertices to 200
		manipulator->setVertexColorAlpha(tangentSphereMesh, 200);

		// scale the mesh by factor 50
		core::matrix4 m;
		m.setScale ( core::vector3df(50,50,50) );
		manipulator->transformMesh( tangentSphereMesh, m );

		sphere = smgr->addMeshSceneNode(tangentSphereMesh);

		sphere->setPosition(core::vector3df(-70,130,45));

		// load heightmap, create normal map from it and set it
		video::ITexture* earthNormalMap = driver->getTexture("../../media/earthbump.bmp");
		driver->makeNormalMapTexture(earthNormalMap, 20.0f);
		sphere->setMaterialTexture(1, earthNormalMap);

		// adjust material settings
		sphere->setMaterialFlag(video::EMF_FOG_ENABLE, true);
		sphere->setMaterialType(video::EMT_NORMAL_MAP_TRANSPARENT_VERTEX_ALPHA);

		// add rotation animator
		scene::ISceneNodeAnimator* anim =
			smgr->createRotationAnimator(core::vector3df(0,0.1f,0));
		sphere->addAnimator(anim);
		anim->drop();

		// drop mesh because we created it with a create.. call.
		tangentSphereMesh->drop();
	}

	/*
	Per pixel lighted materials only look cool when there are moving lights. So we
	add some. And because moving lights alone are so boring, we add billboards
	to them, and a whole particle system to one of them.
	We start with the first light which is red and has only the billboard attached.
	*/

	// add light 1 (nearly red)
	scene::ILightSceneNode* light1 =
		smgr->addLightSceneNode(0, core::vector3df(0,0,0),
		video::SColorf(0.5f, 1.0f, 0.5f, 0.0f), 800.0f);


	// add fly circle animator to light 1
	scene::ISceneNodeAnimator* anim =
		smgr->createFlyCircleAnimator (core::vector3df(50,300,0),190.0f, -0.003f);
	light1->addAnimator(anim);
	anim->drop();

	// attach billboard to the light
	scene::ISceneNode* bill =
		smgr->addBillboardSceneNode(light1, core::dimension2d<f32>(60, 60));

	bill->setMaterialFlag(video::EMF_LIGHTING, false);
	bill->setMaterialFlag(video::EMF_ZWRITE_ENABLE, false);
	bill->setMaterialType(video::EMT_TRANSPARENT_ADD_COLOR);
	bill->setMaterialTexture(0, driver->getTexture("../../media/particlered.bmp"));

	/*
	Now the same again, with the second light. The difference is that we add a particle
	system to it too. And because the light moves, the particles of the particlesystem
	will follow. If you want to know more about how particle systems are created in
	Irrlicht, take a look at the specialFx example.
	Maybe you will have noticed that we only add 2 lights, this has a simple reason: The
	low end version of this material was written in ps1.1 and vs1.1, which doesn't allow
	more lights. You could add a third light to the scene, but it won't be used to
	shade the walls. But of course, this will change in future versions of Irrlicht were
	higher versions of pixel/vertex shaders will be implemented too.
	*/

	// add light 2 (gray)
	scene::ISceneNode* light2 =
		smgr->addLightSceneNode(0, core::vector3df(0,0,0),
		video::SColorf(1.0f, 0.2f, 0.2f, 0.0f), 800.0f);

	// add fly circle animator to light 2
	anim = smgr->createFlyCircleAnimator (core::vector3df(0,150,0),200.0f, 0.001f, core::vector3df ( 0.2f, 0.9f, 0.f ));
	light2->addAnimator(anim);
	anim->drop();

	// attach billboard to light
	bill = smgr->addBillboardSceneNode(light2, core::dimension2d<f32>(120, 120));
	bill->setMaterialFlag(video::EMF_LIGHTING, false);
	bill->setMaterialFlag(video::EMF_ZWRITE_ENABLE, false);
	bill->setMaterialType(video::EMT_TRANSPARENT_ADD_COLOR);
	bill->setMaterialTexture(0, driver->getTexture("../../media/particlewhite.bmp"));

	// add particle system
	scene::IParticleSystemSceneNode* ps =
		smgr->addParticleSystemSceneNode(false, light2);

	ps->setParticleSize(core::dimension2d<f32>(30.0f, 40.0f));

	// create and set emitter
	scene::IParticleEmitter* em = ps->createBoxEmitter(
		core::aabbox3d<f32>(-3,0,-3,3,1,3),
		core::vector3df(0.0f,0.03f,0.0f),
		80,100,
		video::SColor(0,255,255,255), video::SColor(0,255,255,255),
		400,1100);
	ps->setEmitter(em);
	em->drop();

	// create and set affector
	scene::IParticleAffector* paf = ps->createFadeOutParticleAffector();
	ps->addAffector(paf);
	paf->drop();

	// adjust some material settings
	ps->setMaterialFlag(video::EMF_LIGHTING, false);
	ps->setMaterialFlag(video::EMF_ZWRITE_ENABLE, false);
	ps->setMaterialTexture(0, driver->getTexture("../../media/fireball.bmp"));
	ps->setMaterialType(video::EMT_TRANSPARENT_VERTEX_ALPHA);


	MyEventReceiver receiver(room, env, driver);
	device->setEventReceiver(&receiver);

	/*
	Finally, draw everything. That's it.
	*/

	int lastFPS = -1;
	u32 vertexAlpha = 200;
	u32 lastTime = device->getTimer()->getTime();
	bool down = true;


	while(device->run())
	if (device->isWindowActive())
	{
		driver->beginScene(true, true, 0);

		smgr->drawAll();
		env->drawAll();

		driver->endScene();

        ///check if you inc or dec the vertexAlpha value
		if(vertexAlpha < 1 && down)
		down = false;
		else if(vertexAlpha > 254 && !down)
		down = true;

        ///only change every 75 ms so you can see the effect
        u32 thisTime = device->getTimer()->getTime();
        if((lastTime + 75) < thisTime && down)
        {
            smgr->getMeshManipulator()->setVertexColorAlpha(sphere->getMesh(), --vertexAlpha);
            lastTime = thisTime;
        }
        else
            if(!down && (lastTime + 75) < thisTime)
            {
            smgr->getMeshManipulator()->setVertexColorAlpha(sphere->getMesh(), ++vertexAlpha);
            lastTime = thisTime;
            };

        printf("vertexAlpha: %i\n", vertexAlpha);

		int fps = driver->getFPS();

		if (lastFPS != fps)
		{
			core::stringw str = L"Per pixel lighting example || FadeIN/OUT MOD - Irrlicht Engine [";
			str += driver->getName();
			str += "] FPS:";
			str += fps;

			device->setWindowCaption(str.c_str());
			lastFPS = fps;
		}
	}

	device->drop();

	return 0;
}

-you might have a look at the earth mesh's construction function, this is what you need to do with the meshs you want to fade.

what you could do now is add a deletion animator to the sphere node when a specified time exceeded, to delete the node...

[Adversus]

i.e. Creating a copy of the mesh and changing vertex colors.

All I want to do is fade an object in and out. Is it not possible to use the color stored in the diffuse of the material like OpenGL? Even if it means writing a new SceneNode and/or Material Renderer?

I might be wrong, my OGL is rusty however with this approach I think I would need to turn on lighting (no issue as I want that anyway, I can make something visible if it's dark by setting emissive) and change the alpha of all the diffuse materials of the mesh when rendering.

Apart from the material renderer, I would also need to handle instancing when changing these materials so the original doesn't change.

Is this possible, would this be faster. Or is changing the vertex colors for each instance a better solution, it's certainly simpler.

[sudi]

Use a shader. thats the easiest way i can come up with.

[mk.1]

This has been requested a lot of times but never been worked on.
Best solution (imo) is to add an "alpha" value to scene nodes that is used in the fixed function pipeline. I've done that in dx so it should be possible with openGL as well. Since I don't know sh*t about openGL I never came up with a fully working solution (that supports all renderers)

[Halifax]

Use a shader. thats the easiest way i can come up with.

Yeah, I agree with that statement. Just throw a little depth check in there and blend accordingly. If you want to have a sphere as an influence, instead of a linear line, just calculate the distance and use that to set your alpha. You could include some parameters to modify how your algorithm works as well such as how steep the falloff is, etc.

I'm guessing you're going to use this for a LOD system, similar to GTA IV?

[Adversus]

I thought some people may be interested as it's been requested:

Code: Select all

::SetAlpha( f32 alpha )
{
	// transparent?
	if( alpha < 1.0 )
		parent.GetSceneManager().registerNodeForRendering( meshSceneNode, ESNRP_TRANSPARENT );
	else
		parent.GetSceneManager().registerNodeForRendering( meshSceneNode, ESNRP_SOLID );
	
	// set the alpha
	for( int i=0; i < meshSceneNode->getMaterialCount(); i++ )
	{
		// get the material
		video::SMaterial &material = meshSceneNode->getMaterial(i);
		material.MaterialType = video::EMT_ONETEXTURE_BLEND;
		material.MaterialTypeParam = video::pack_texureBlendFunc( video::EBF_SRC_ALPHA, video::EBF_ONE_MINUS_SRC_ALPHA, video::EMFN_MODULATE_1X );
		material.Lighting = true;
		material.ZWriteEnable = true;
		material.DiffuseColor.setAlpha(alpha*255);
	}

The only problem with this method is that it turns on alpha testing and uses texture combiners in OGL when it doesn't really need to. The other thing is that ir requires lighting however you can just set the emissive color so that's no big deal. As I'm developing on iPhone I'm just going to comment all the stuff out it doesn't require from the driver.

On another note, as some people suggested chaning the vertex color. Personally I don't even know why color vertex buffers are even used (except maybe for transparency for lightmaps however this could be set with one glColor command), I don't think modifying the buffers for every instance every frame is really a solution.