Volumetrics beta 0.9 : Isosurface landscape tutorial.

Introduction

This tutorial explains how to create a landscape with isosurfaces. It is assumed that you have already read the MojoWorld manual and learned something about MojoWorld itself, and also read volumetrics's readme. I.e. instead of writing "click on the cloud-like icon" I am going to write "Open the Sky Editor" and so-on :-) I might add icons later, have no time...

Instructions:

  1. Start from a blank planet. Open the Sky Editor and and select Volumetrics in the Atmosphere DDLB. Unfold the Volumetrics (click on >) to see parameters. For meaning of parameters, consult the tooltips.
  2. At the end of list of parameters, there's DDLB labelled 0 Click on it to see menu. (Note that there is Load and Save options in menu.) Select Surface in the menu to create isosurface (note how you also get another DDLB labelled 1). Open the SURFACE EDITOR window by clicking on [<].
  3. Similarly, select 'Simple shader' in the Shader DDLB. Without shader it would be unshaded gray, and shape wouldn't be visible...

    4. Some explanations: The Isosurface's shape is defined by Shape parameter. It is very simple in concept: where Shape is greater than zero, you get clean air, and where Shape is smaller than zero, you get solid (e.g. rock). Roughly speaking, when Volumetrics render the isosurface, it computes the value of Shape in space all around and looks if it is greater or smaller than zero (if greater assumes there's clean air and light can pass through, if smaller, assumes that there's rock. All mojoworld textures exist not only on planet but everywhere all around, and isosurface uses that). The surface itself is placed where Shape is equal to zero.(More on that below.)
    Additionally, Isosurface is contained between Lowest altitude and Highest altitude , this allows you to avoid say getting blobs going all way to the infinity.

    Important note: if the camera is located within the surface, you will get some special color in the RTR and in the render. In such case, move the camera around or get above the highest altitude.

  4. To avoid getting holes in the ground where altitude of your terrain is smaller than Lowest altitude, set the Lowest altitude to be really negative, like -100 000 . Do that for any isosurface landscape you create, unless you want to get holes :-) By the way, don't do similar thing with Highest altitude, or it will render slowly because volumetrics will need to check this empty air (volumetrics is smart enough to avoid checking empty air much, but it doesn't know much about what terrain you make, better to give a hint with higher altitude )...
  5. Create the texture for isosurface's Shape parameter
    (click on semi-circle, in menu select Texture, texture editor will open, select New Texture in menu)
  6. Create two Texture Leaves.
  7. In the first texture leaf, replace "Monofractal" with "None" and replace "World Position" with "Altitude".
  8. Set Blend Type to Subtract
  9. In the second texture leaf, set monofractal's Result Scale to say 200.
  10. Open Objects List (if you don't know what it is, consult MW manual) and make planet invisible (so we won't see mojo's planet together with isosurface planet)
  11. Render it. You should get isosurface landscape. You might see some artifacts in render in this case try increasing Reliability and maybe increase Refinement Steps to 10. Also it is important to keep RTR turned on, it are doing some automatic adjustment stuff as you go.
Now you can (for example) save this isosurface layer to the library, so next time you start doing isosurface landscape, instead of creating new generic isosurface, you can load this library file.

Explanations, and how to use the knowledge to make new landscapes

Some simple mathematics

(don't worry and don't skip this section, it's really simple, just some info on how Subtract works, like 2-2=0 :-) )
As have been mentioned above, sign (as in 'negative or positive') of Shape simply defines where you have solid and where you don't.
In the texture, we made Shape to be equal to

[First Leaf,altitude] minus [Second Leaf,sorta height] (that's how blend by subtract works in MojoWorld).

Now some elementary school math: the result of subtraction is negative when first value is smaller than second. It is equal to zero if and only if both parameters is equal. That is, you get zero where Altitude is equal to [second texture leaf]
Quoting from above,"The surface itself is placed where Shape is equal to zero."
Therefore, isosurface is placed where altitude is equal to second texture leaf.
Second leaf behaves "almost" like MojoWorld's "Mountain Height"(A.K.A land texture). Below there's more info on this almost, and how to make this "almost" be "identical".

World Position and Surface Position

First, some drawing that explains what is World Position and what is Surface Position in the MojoWorld:

(from now on, World Position and Surface Position is abbrevated as WorldPos and SurfacePos)

 WorldPos(red) it's point where texture are evaluated. SurfacePos (blue) is computed from WorldPos as shown on image. Two example points A and B is shown to display that it works in same way for point below and above zero altitude.
If you feed WorldPos to fractal, fractal will be computed in the red point,
if you feed SurfacePos, fractal will be computed in blue point.
The main difference is that for all points along some green line you will get same SurfacePos.

MojoWorld Landscapes and Isosurface Landscapes

If you do the landscape as described above, the second texture leaf will define the terrain "almost" same as normal MojoWorld's Mountain Height texture (that defines MojoWorld's landscape)
The main difference is that (as explained in MojoWorld manual and elsewhere), in the MojoWorld's "Mountain Height", there's in fact no WorldPos:
In the MojoWorld's Mountain Height WorldPos is always equal to SurfacePos.

In the Isosurfaces, WorldPos is always the point "somewhere in the air" where Volumetrics renderer is checking the sign of Shape to find if it is empty or not.

If you replace World Position by Surface Position, you get terrain that will be identical to what you'd get if you'd have second leaf ALONE in the MojoWorld's Mountain Height. But it is not really recommended for simple terrains - this way you lose many of benefits of using Isosurface. For example, using WorldPos in Shape let you easily create overhangs (no need to mess with displacements) by simply increasing Result Scale of fractal. (tho if you increase it too much you may get some floating things *) In Function Graph, you can use best of both methods - linear blend of World Position and Surface Position (btw, driving blend value with fractals(esp. rough ones) is -not- recommended, it will not really do what you'd expect).
(* floating things is defined by shape just like terrain, so there's only two ways to get rid of floating things: make Shape that doesn't define any floaters, or paint floaters out in postwork. First method is preferred, you can achieve that by using smaller result scales or by using linear blend of World Position and Surface Position to get best result. Second method is kind of more artist-friendly. Also it is not easy to make terrain with holes but without floating bits)


The tutorial is quite brief so you need to read the explanations and make sure you understand them.
After completing this tutorial you should be able to do same thing with function graph. Create Subtract node, to the left side connect altitude, to the right side connect the fractal, connect output of subtract to "Input".
Things to try next:
Try replacing World Position with linear blend of World Position and Surface Position.
Try selecting some distortion in the first leaf (where you have altitude), you may get very interesting results.
Look at sample world files.