Landscape Texture Constraints

Introduction

A TileSet is part of the TileBank. There are sevral TileSet in a TileBank. A TileSet is a kind of material (like grass, wood, rock).

This material is divided in small textures (128x128), large textures (256x256) and transition textures (128x128 alpha).

See File Conversion Graph for details on the build process.

Small and Large Textures

A tile in the NeL landscape is a bitmap with a size of 128x128. A patch can have 2x2 tiles, 4x4 tiles, 8x8 tiles and 16x16 tiles. But to have bitmaps with a better quality, we can use larges textures (256x256) as 4 tiles.

In the painter plugin, you can choose to paint 128x128 bitmaps or 256x256 bitmaps. The pixel ratio stays the same.

All the textures have two channels: diffuse and additive. We use a bitmap for diffuse and another one for additive.

Transition Textures

Transition textures are used to make smooth Tileset changes. To do this, we have a set of 48 transition textures. With this set, we can make all transition we want with some diversity (two type of transitions are randomly choosen to increase diversity).

Transition textures are bitmaps of 128x128 pixel with a third channel: an alpha channel. This channel is a grayscale bitmap. It is used to make the transition like this:

A tile transition [layer (2)] is used as an alpha layer between the two tiles [layers (1) & (3)] giving a smoothed transition between different tile sets.

Results in this tile being displayed.

Here is the transitions set:

This is the 48 alpha bitmaps you need to build your bank.

Orange pixels are alpha=255 and black pixels are alpha=0.

In fact, you only need to draw 12 alpha bitmaps to fill this bank. The others are computed with a rotation. Here is the 12 alpha bitmaps you really need:

The batchload function of tile_edit.exe load all the alpha transitions in one shot. To use the batchload function, the alpha bitmaps must have a name like wood_alpha00.tga, wood_alpha01.tga. The number of a transition tile is given by its position in the previous set. The first (left, top) is number 00, and so on, first to the right then to the bottom.

Bitmap Check

To avoid bilinear discontinuity using tiles, tile_edit.exe performs some checks to be sure bilinear filtering will work.

Each time you add a bitmap in tile_edit.exe, by drag and drop or with the "add" or "replace" functions, the program checks the tile pixels. The tiles must follow whose rules:

128x128 bitmaps must have the same top and bottom pixel row.
128x128 bitmaps must have the same left and right pixel column.
256x256 bitmaps must have two times the 128x128 pixel row at top and bottom.
256x256 bitmaps must have two times the 128x128 pixel column at left and right.
Two transitions with the same kind of border must have same pixel border. For example, check the transition 0 right border and transition 1 left border. They have the same type. So, the right pixel column of transition 0 must be the same than the left pixel column of transition 1.

Two transitions with the same kind of border must have same pixel border. For example, check the transition 0 right border and transition 1 left border. They have the same type. So, the right pixel column of transition 0 must be the same than the left pixel column of transition 1.

You can see in the above picture a 128x128 bitmap with its U and V pixel borders and a 256x256 bitmap with the double U and V pixel border.

From Old Wiki
Creating the textures is the trickiest part of creating the tile bank. There are tiling restrictions outlined below that make it more difficult to create the textures. In addition you need to avoid any extremes of light or dark in the tiles so patterns are not obvious when you tile them together.
The tile format MUST be an uncompressed TGA image. Two sizes are 128x128 and 256x256 pixels, you can use either 24 or 32 bit images.
Most importantly the border of an image must be mapped as below, the left and right edges MUST be EXACTLY the same, the top and bottom edges MUST be EXACTLY the same, the entire border ( all four edges ) MUST be the same as EVERY other tile in that TileSet.
If you have a TileSet for autumn forest grass type b then any grass tile in this set must have EXACTLY the same border.
A Border is a band one pixel wide that follows the edge of the ENTIRE image.
The 256x256 tiles MUST have two of each 128x128 border edge side by side as shown in the images below. This enables 256x256 tiles to link with 128x128 tiles seamlessly.