Alpha blending

[Schakal]

Hi all,
i am new to Irrlicht
And soon I got my first problem:
I want to make an isometric game.
I made two pictures, the one is grass and the other shall be a mask with a isometric shape:





And my goal is to lay the mask over the grass so that i get grass in isometric shape
So far so good, ... but how can I do it with Irrlicht?
I guess something like that has been often talked about in this forum,
but my keywords weren't good enough to find a solution =(

Thx for help!
David

[Bear_130278]

One of the ways:
1.Make a texture with alpha channel, tga for example
2.Make a plane and use this texture as the map for desired polygon.
3.Set the MaterialType = EMT_TRANSPARENT_ALPHA_CHANNEL_REF

Voila! You got what you wanted
But this is stupid brute force , a fake 2D graphics ))

It is much wiser to set up the camera of the engine, to work as an orthographic one ))
So make any landscape you want, place it on the scene, and make ortho camera - you got what you need in a 3D fashion

[arras]

If you want to do it yourself you can access grass texture loaded in to Irrlicht via lock/unlock function and manually edit pixels alpha based on mask. Or use IImage interface for the same purpose.

Easier way is to load your texture with mask already.
Two ways:
Use tga as suggested since it supports alpha.
Or use makeColorKeyTexture() function from videodriver ...look at description for more info.

[Dark_Kilauea]

Or you could do that step in the art pipeline, using a program like GIMP. Prevents you from having to do it later in the program, increasing the time to render each frame or load the application.

[Schakal]

@Bear: Sounds reasonable!

@arras:
I tried this code:

Code: Select all

void MaskImage(video::ITexture* image,video::ITexture* mask,core::rect<s32> type)
{
   s32* ibuf = (s32*)image->lock();
   s32* mbuf = (s32*)mask->lock();


   for(int x = type.UpperLeftCorner.X;x<type.LowerRightCorner.X;x++)
   {
      for(int y = type.UpperLeftCorner.Y;y<type.LowerRightCorner.Y;y++)
      {
         *((u8*)ibuf+image->getPitch()*y+x*4+3)=255; //*((u8*)mbuf+mask->getPitch()*y+x*4+3);
      }
   }
   image->unlock();
   mask->unlock();
}

But I get some kind of memory error there =/

@Dark_Kilauea:
I prefer to render it at the start of the application,
because otherwise I would need X*Y images (X=tile sorts, Y=masks)
And that would be really much after some time =)


Thx for your help!!

[bitplane]

You need a pixel shader that does-

Code: Select all

destination = (source1*mask) + (source2*(1-mask));

[grafikrobot]

You need a pixel shader that does-

Code: Select all

destination = (source1*mask) + (source2*(1-mask));

Or you could do it with a multi-texture op.

[Schakal]

Ok guys,
I got a bit further with my problem:

I just wrote "x*2" instead of "x*4".
The result was a blue version of my grass
So x*2 would mean (because each single pixel is changed),
that my texture has a 8-bit format (4bit*2)
And it seems that
I cant change the alpha value.
So I guess that I have to change the format of the texture?!
And how to do that?!

Edit:
Ok, to change the bit format I have used
driver->setTextureCreationFlag(ETCF_ALWAYS_32_BIT,true);
But it seems that nothing has changed now?!

Well, I think that won't ever work, so new run:

Code: Select all

void MaskImage(video::ITexture* image,video::ITexture* mask,core::rect<s32> type)
{
   SMaterial* mymat  = new SMaterial;
   mymat->setTexture(1,image);
   mymat->setTexture(2,mask);
   mymat->MaterialType = EMT_TRANSPARENT_ALPHA_CHANNEL_REF;

   // ....

Inspired by Bear_130278 i try this. But do I need now barely a plane or can I make SMaterial into ITexture* ??

[hybrid]

Be careful with 'new', this one looks incorrect at this place...
Anyway, there's no way to p a material into a texture, it's the other way round. Still, you cannot use a material to do 2d rendering, because the 2d methods have their own set of parameters. You have to use those, there's no other way. And 2d just uses 1 texture, so no way to use an alpha mask texture. Anyway, Irrlicht doesn't support alpha maps at all.
Ok, final point, try to check the texture format before writing into arbitrary memory positions.

[Pyritie]

Be careful with 'new', this one looks incorrect at this place...
Anyway, there's no way to p a material into a texture, it's the other way round. Still, you cannot use a material to do 2d rendering, because the 2d methods have their own set of parameters. You have to use those, there's no other way. And 2d just uses 1 texture, so no way to use an alpha mask texture. Anyway, Irrlicht doesn't support alpha maps at all.
Ok, final point, try to check the texture format before writing into arbitrary memory positions.

What do we use for transparent textures then? PNGs, TGAs with alpha channel (which after this I assume is a no), or something else?

[hybrid]

Irrlicht supports the alpha channel, but not mixing one diffuse texture with another channel from a second texture. But once you check the 2d methods you'll find a hint for alpha channel and vertex alpha, and both are fully functional! We even have examples showing how to do this