Translucent ITexture (load from png) Fade out animation

[jack_fantasy]

Hi, everyone

I have a set of image mesh scene nodes, their textures are loaded from translucent pngs (some parts may have 0.0 alpha other parts may have 1.0 alpha). I set their MaterialType to video::EMT_TRANSPARENT_ALPHA_CHANNEL. Image mesh scene nodes are rendered as expected.

My question is how to create the fade out animation on my image scene nodes in irrlicht without manipulating alpha in the pixel shader?

My original thought we could use blend operation similar to using GL_CONSTANT_ALPHA and glBlendFunc in OpenGL. But I couldn't find a GL_CONSTANT_ALPHA equivalent in irrlicht.

Thank you,
jack_fantasy

[hendu]

For what you need, writing a shader is the simplest solution.

[jack_fantasy]

Thank you, hendu

For what you need, writing a shader is the simplest solution.

Right, I thought that could be done by a shader. I have a hierarchy of custom scene node classes (some of them already requiring a shader), if I need a unified way to create a fade out animation for my scene nodes. I have to create a shader for every classes and I also need to override some shaders in my class hierarchy. Suddenly a fade out animation problem becomes an architecture design problem which I am trying to avoid. Do we have any other alternatives to solve this problem in irrlicht?

Jack_fantasy

[CuteAlien]

Would have to experiment myself. But maybe you could set EMT_TRANSPARENT_VERTEX_ALPHA and then change the alpha values of the mesh-vertices. Thought you'd have to ensure each node has it's own mesh (so they don't affect each other) and not sure if it's still useable if you need to mix it with other alpha values (like texture alpha).

[jack_fantasy]

Thanks, CuteAlien

I have tried EMT_TRANSPARENT_VERTEX_ALPHA with a custom vertex colour. I think EMT_TRANSPARENT_VERTEX_ALPHA only takes the vertex alpha into account, not the texture alpha.

I have tried combinations of EMT_TRANSPARENT_VERTEX_ALPHA, EMT_TRANSPARENT_ALPHA_CHANNEL and EMT_ONETEXTURE_BLEND with following code:

Code: Select all

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, 
                video::EAS_TEXTURE | video::EAS_VERTEX_COLOR);
 
smgr->MeshManipulator->setVertexColor(mesh, SColor(127,0,0,0)); 

It doesn't work, only take one alpha value into account.

I am looking for a simple mechanism (a root alpha value) to control the scene node transparency regardless how many alpha values in various parts of the scene node.

jack_fantasy

[hendu]

There isn't one. The built-in materials all only take one alpha, for more than that you have to use shaders.

If some of your nodes already use shaders, you cannot override their alpha output with material flags anyhow.


If you need to fade them all out in unison, maybe you could use a RTT? Render them into it, then fade that RTT out in a single shader.

[jack_fantasy]

Thanks, hendu

It looks like this is not simple problem as I thought. There are a few threads about this topic. People have already asked something like what I thought. Probably, I have to go with manipulating alphas in shaders at this stage.

jack_fantasy