Enticide 101 - Removing Tree Roots in Bryce.
Ever felt the need to put a tree on the edge of something or into a pot and had roots sticking through a wall, or out through the side of the pot? How about using tree's as branches to make an uber-tree, and had roots sticking out into mid air..... well, here's one way to easily de-root your bryce tree using a simple transparency map.
Step 1 - Preparation
For this tut, I'm looking at putting a shrub (which I've made from a bryce tree using AgentSmiths piece of LA flora for the leaf textures) into a pot. It all looks reasonably good, except for those roots sticking out through the bottom of the pot, and thats what we want to work on.
So after you've come up with the tree that you want to put into your scene, its time to go to work on those roots. Firstly, pull your tree off to the side of the thing its going to go into - this will help you see whats going on later in proceedings.
Step 2 - The Tree Trunk Texture
What we now want to do is to apply a specific transparency map to the trunk of the tree.
So to do this, firstly select the tree and then click on the 'e' button to bring up the tree lab. Now in the tree lab, click on the material editor for the tree trunk as shown.
What you can now see is the material that is being applied to the tree trunk and the branches of the tree. Here the branch and trunk texture is a photo based texture (tex A) which includes both the texture and a bump map. So what we want to do now is to apply a transmap to this texture to in effect make the bottom part of the tree (the roots) invisible.
Step 3 - Loading The Transparency Map
Click on the second dot in the transparency row - this will bring up a new texture entry on the right hand side of the material editor. On this new texture entry on the right hand side, click on the approrpiate dots to open the picture library window.
Once in here, load an image that looks like what I've shown into the middle of the three texture boxes. In this image, the black parts will correspond to those parts of the tree that will become transparent and the white part will correspond to which part of the tree will remain visible. For this case, I've gone for about a 2/3 white, 1/3 black - thus the top 2/3s of the tree will remain visible, while hopefully the bottom 1/3 will become transparent. If, on the other hand, you wanted to chop the top of the tree off, you could use an image where the top part was black and the bottom part was white.
Once you've loaded your transparency map into the library, click on the tick symbol to go back to the mat editor.
Step 4 - Texture Positioning
After you've done that, make sure the blend transparency option is ticked - its not necessary for the workings of this tutorial to do that, but its always something to check for if your transparency maps aren't working the way you think they should be. Also, set the mapping mode to object front - this seems to be the simplest option when visualizing whats going on with the transparency map.
If we now render the tree, we'll notice that it looks like a bit has been cut out of the trunk of the tree, however the bit may not be in the correct position.
What you've now got to do is a little bit of trial and error to position the transparency map so that it deletes all of the roots and not any of the top of the tree. This is easiest done by altering the offset values for the texture in the 'y' (vertical up and down) direction. In the above image you can see the effect on the transparency with 0, 10, 40 units of offset (the leaves have been removed from the tree to help show whats going on). The more the offset, the lower the boundary between visible and transparent is moved. Find the value for the offset at which the roots and enough of the trunk are now invisible for your purpose - in my case, 40 units of offset in the y direction was enough.
Step 5 - Finish
Once you've found an offset value that will have the effect of making the tree roots invisible, you can move your tree back into its pot, or the branchs back onto your ent to get the desired result.
If you have any questions concerning this tutorial, feel free to send me an email at firstname.lastname@example.org (make sure you spell that email address properly) and we'll see if we can find you an answer.