If you're new to Leveller, or to pixel-based editors in
general, then this tutorial is for you. It covers the
basics of using the Leveller tools to sculpt a heightfield.
Leveller's user interface was influenced by Paint Shop Pro 4
and Adobe Photoshop. If you use either of those
programs, you'll probably see the similarities. We wanted to
make it easy for users of other graphics software to use Leveller.
Basic Concepts
A heightfield, like a bitmap, is composed of discrete
point samples called pixels. Instead of a color, however,
each pixel contains an elevation value. Heightfields are
discussed in more depth here.
Most of Leveller's editing tools use a setting called
the current brush size. This is simply a number
which specifies how wide, in pixels, the region under
the mouse pointer will be affected when a tool is used.
The spatial reference system used is based on simple
cartography. In painting, one uses words like "top"
to mean the first scanline of a bitmap. With heightfields,
however, "top" could also mean the top of a peak.
As the diagram below shows, the preferred nomenclature
is to use compass directions.
The north-south distance is the heightfield's breadth,
because using the word "height" could mean the elevation height.
Speaking of which, the distance from the lowest elevation to
the highest is called the span.
Like a paint program, Leveller makes extensive use of
selection masks. These are simply user-defined
regions of the heightfield that control where sculpting
and filtering effects can occur. The picture below
shows an example of a discontinuous selection mask,
because the selected regions are not connected to
each other.
Naturally, a selection mask is also composed of pixels.
Since each such pixel has an 8-bit value, it is possible
to make the mask behave as an alpha channel, where
some regions are "more selected" than others. For example,
if you "strongly selected" one area and "lightly selected"
another, and then proceeded to use the Dig tool, the
latter region wouldn't be dug as deeply as the former.
By default, Leveller documents start off with no
selection mask, which means that every heightfield
pixel is fully selected. As you use the editing tools,
however, you will want to use masks to assert more control
and make fine-tuned edits.
Selection masks are also used to support the Cut/Copy/Paste
commands in the Edit menu. To copy the entire heightfield
to the clipboard, for example, you would choose
Selection, Select All, and then Edit, Copy.
Selections are also used to control object placement
in the POV-Ray export. The forest
tutorial explains how.
And finally, there is the colormap. This is simply
how heightfields are colored so that you can tell (when
looking from overhead, anyway), which parts have which elevations.
You can use the View, Colormap... command to choose
which colormap to use.
Primary Sculpting Tools
The primary editing tools are Dig, Raise, and Flatten
(also, when you use the Delete key to flatten the
currently selected area, it is the elevation setting
of the Flatten tool that is used). These tools directly
modify the elevation of heightfield pixels wherever
the mouse is dragged over the map, between pushing the mouse
button down and releasing it.
If you have selected an area, only the pixels within
the area will be affected.
Every tool has a tool settings panel. This lets
you customize the tool to work a certain way.
Here's what the effects of the Flatten and Dig/Raise
tools look like:
Selection Tools
These tools let you create selection masks:
When selecting, hold the Shift key down to extend the
current selection. Hold the Ctrl key down to subtract
from the current selection.
All the selection tools create "fully selected" regions.
To make the edges of the selection "lightly selected",
use the Selection, Feather command. You can modify the
current selection mask in more ways with the other
commands in the Selection menu.
Filtering
Filters are processes that work on all the pixels
within the current selection at once. This makes
them faster than doing the same process with the
editing tools. Judicious mixing of filters, tools,
and selection masks, of course, makes for
very powerful modeling.
The filters are available in the Filter menu.
The first bunch are "core" filters because they
are built-in to Leveller itself; the rest are
plug-in based, so their availability depends on
which plug-ins have been installed.
The core filters do fundamental operations, such
as inversion, flipping, scaling, rotation, clipping,
combining, etc. The pictures below show the effects
of the Clip, Slide, and Terrace filters.
The plug-in filters provide terrain generation
and more exotic effects.
Rectangular Select
Makes rectangular selections. Click and drag to define
the rectangle's opposing corners. The tool settings let you
constrain the rectangle to a square or to a line.
Elliptical Select
Makes oval-shaped selections. Click and drag to define
the containing rectangle's opposing corners. The tool settings let you
constrain the oval to a circle or to an ellipse of specific thickness.
Arbitrary Select
Makes irregular-shaped selections. Click and drag to define the border
of the selected region. When the mouse is released, the starting/ending
points of the mousedrag will be joined by a straight line.
Magic Wand
Selects areas of similar elevation. Simply define the tool settings
and click on a heightfield pixel to create the selection.
