Irrlicht Engine

First load any "empty" texture.
Then use the getColorFormat() function of texture to get the color format and lock() function to get pointer to pixels.
Also load the texture of grass, sand... and do the same.

Now it's up to you to calculate the position of "brush" and blend the fragment of grass ...

camera->setTarget(vector);

http://irrlicht.sourceforge.net/docu/cl ... e.html#a20

Did you read API documentation??