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195 lines
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HTML
195 lines
11 KiB
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<meta http-equiv="Content-Type" content="text/html; charset=windows-1252">
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<meta name="GENERATOR" content="Microsoft FrontPage 4.0">
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<meta name="ProgId" content="FrontPage.Editor.Document">
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<title>Creating the Alphamap</title>
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<body background="../pics/background.jpg" text="#FFFFFF" link="#FFFFFF" vlink="#FFFFFF" alink="#FFFFFF">
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<b>
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<p align="center"><font size="5">Creating the Alphamap</font></p>
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<div align="right">
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<table border="1" cellspacing="1" width="100%" bordercolor="#808080" bgcolor="#000000" cellpadding="10">
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<tr>
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<td width="100%"><font FACE="Times New Roman">
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<p> The alphamap referenced by the alphamap key/value pair is an art file created
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specifically for the map. For non-digital artists, it may be one of the more
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technically and conceptually challenging things that need to be created to make
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the terrain map work.</p>
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<p> Simply put, the alpha map is the template that the compiler uses to assign
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textures to the terrain surface.</p>
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<p> To make the alphamap, you must have, or have access to, an art program that
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can save a file as an 8-bit BMP file with indexed color. I<>ll discuss other
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file types later on, but the BMP file is probably the simplest solution, both
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technically and conceptually.</p>
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<p> </p>
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</font><b><font SIZE="4">
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<p>Terms</p>
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</font></b><font FACE="Times New Roman">
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<p> First, you need to understand a couple vocabulary words <20> jargon, if you
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will:</p>
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<b>
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<p>Indexed Color:</b> In essence, each color used in a piece of art is
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remembered by its location on the color table or palette (see below). There are
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256 colors available, numbered from 0 to 255. Each position on the palette has
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its own number. This number has nothing to do with the RGB values of a color in
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that position. If you change the actual color located at a particular location
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on the palette (say from red to blue), all the pixels that were formerly that
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shade of red (if painted using a color with that index number), will change to
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the new color of blue.</p>
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<b>
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<p>Color Table:</b> This is what Photoshop calls the indexed color layout of 256
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colors. In Paint Shop Pro it<69>s a palette. This is a pop-up window that shows
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the colors in the palette and their arrangement. For making an alphamap for a
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terrain map, the colors you choose are not important, but their position on the
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palette is.</p>
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<b>
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<p>Palette:</b> This is what Paint Shop Pro calls a Color Table.</p>
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<p> </p>
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</font><b><font SIZE="4">
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<p>Making the Palette</p>
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</font></b><font FACE="Times New Roman">
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<p> The best way to start is to make a set of colors to use when painting
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alphamaps. If you want, you can do this once and save it out. In PSP edit the
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palette (in Photoshop, open the Color Table). Make sure the colors are sorted by
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index number (there may be a pull down menu that allows this). In PSP, the
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colors are indexed from the upper left (color 0 in the upper leftmost position
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and increasing in value to the right). In Photoshop, the positions are reversed.
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The color with value 0 is in the lower rightmost position and the index numbers
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increase to the right.</p>
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<p> Because there is a direct one-to-one relationship between colors in the
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palette and individual shaders that make of the metashader, you should select
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clearly distinct colors to represent each shader. You should have one color for
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each layer you intend to include in the map (see keys above), which means one
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color to represent each root shader. You may find it convenient to create more,
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so they are available for later use (if you save the palette).</p>
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<p> This method worked for me to make a 16-color palette in Paint Shop Pro.
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First, I reduced my palette size to 16 colors. I clicked on each palette
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position and created a color for it (don<6F>t use black). Then, I increased my
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palette size back up to 256 colors, filling the rest with black. In Photoshop,
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it<EFBFBD>s easier to select all the colors you don<6F>t intend to use and make them
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black. Then, I save the palette out as a file for later use.</p>
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<p> Another thing you might try is to make a grayscale palette, then use only the
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first few positions for your color and leave the rest for grayscale (this allows
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you to import bmp height maps and use them as guidelines).</p>
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<p> </p>
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</font><b><font SIZE="4">
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<p>Alphamap File Data</p>
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</font></b><font FACE="Times New Roman"><b>
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<p>File type:</b> The alphamap is a BMP format file or a TGA file (see other
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file formats below). With BMP format, each color in your palette corresponds
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directly to a root shader used to create the smooth texture blends on the
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terrain.</p>
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<b>
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<p>File size:</b> The size of the alphamap should be one-to-one with the number
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of vertexes in the map. If you have 64 divisions x 32 divisions in your terrain
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mesh (65x33 vertexes), you should use a 65 by 33 alphamap. You can use an
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alphamap with a size that is not a one-to-one map with the number of map
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vertexes, but you can then expect a less precise interpretation of your texture
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assignments.</p>
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<b>
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<p>Colors linked to Shaders:</b> If an 8-bit texture is used (BMP), q3map links
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a color<6F>s position on the palette to an identifying number in the name of a
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shader. The color in position 0 would reference a root shader named <metashadername>_0.
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The color in position 1 would reference a root shader named <metashadername>_1.
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<metashadername> refers to the value of the Shader key (see Key: Shader
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below). In theory, you could probably have 256 different root shaders assigned
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to the terrain entity. In practice, you<6F>d probably want to bite your arm off
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at the elbow before doing something as complicated as that.</p>
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</font><b><font SIZE="4">
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<p>Other File Formats</p>
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</font></b><font FACE="Times New Roman">
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<p> It is possible to use a TGA file (a RGB color format) for an
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alphamap. TGA
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files are handled differently than indexed color files like BMP. Instead of
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looking for a position on the palette, q3map interprets the RGB value of actual
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color. With a 32-bit TGA file, only the color values in the red channel are
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used. The program assumes that a gray scale of equal values is being used. The
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program divides the colors by the number of levels into equal-sized ranges. When
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assigning textures, q3map looks at what range the color falls in and chooses the
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appropriate shader to place or blend.</p>
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</font><b><font SIZE="4">
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<p>Controlling Texture Blends</p>
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</font></b><font FACE="Times New Roman">
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<p> Each triangle on the mesh can only have two root shaders blending across it.
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Another way to say this is that there should be only two different colors on the
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three vertexes that form any given triangle in the mesh. Any more, and a sharp,
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unblended edge appears on the terrain surface. This can take some trial and
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error to correct. A bsp -switch command called -showseams can help the mapmaker
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find these errors. Create a new bsp command in your project file that includes
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this option. We recommend doing it with a novis only operation.</p>
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</font><font FACE="Times New Roman" SIZE="2">
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<p align="center"><img SRC="Image5.gif" WIDTH="266" HEIGHT="352">
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<img SRC="Image6.gif" WIDTH="264" HEIGHT="352"></p>
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</font><font FACE="Times New Roman">
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<p>Figure 3</p>
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<p> In figure 3, the blue and white image on the left is a scaled up (4X) version
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of the alphamap used on Distant Screams. It shows three different root shaders
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in use. Compare that to the gray scale height map on the right and you can see
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how the artist chose to assign textures to the various heights and depths of the
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map. As long as the guidelines for texture placement are followed, a mapmaker
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should be able to work with more different root shaders than shown here.</p>
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</font><b><font SIZE="4">
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<p>Alphamap Creation Tips:</p>
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<blockquote>
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<blockquote>
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</font></b><font FACE="Symbol" SIZE="2">
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<p><EFBFBD> </font><font FACE="Times New Roman">The alphamaps for the team arena maps
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are included with this document, both as reference and as files that you can
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modify to work with your own maps. You may want to compare the alphamaps against
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the heightmaps for the same maps, just to see how id resolved mapping issues.</p>
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</font><font FACE="Symbol" SIZE="2">
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<p><EFBFBD> </font><font FACE="Times New Roman">You can create a quick (though not
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necessarily good) alphamap by saving your height map as a new file. Then use the
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<EFBFBD>posterize<EFBFBD> filter that can be found in some art tools. Reduce the number of
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colors in the art to equal the layers (number of unique root shaders) in the
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terrain.</p>
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</font><font FACE="Symbol" SIZE="2">
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<p><EFBFBD> </font><font FACE="Times New Roman">If you are creating a new alphamap
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from scratch, use colors that are easily distinguished from each other.</p>
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</font><font FACE="Symbol" SIZE="2">
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<p><EFBFBD> </font><font FACE="Times New Roman">If you are making an alphamap for a
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team style map where both sides of the map are identical (mirrored or rotated),
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you only need to design the map for one side. Copy and position it as described
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above for the heightmap.</p>
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</font><font FACE="Symbol" SIZE="2">
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<p><EFBFBD> </font><font FACE="Times New Roman">The id maps used simple color schemes
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that were homogenous throughout the maps. That is not the only way of doing
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things. It would be quite reasonable to use many more terrain textures
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(particularly if you weren<65>t going to build complicated, multi-texture
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architecture on top of them). Consider a map where one part of the terrain used
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red-themed textures and the other side blue themed textures. Have them blend
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into a few simple neutral colors near the map center.</p>
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</font><font FACE="Symbol" SIZE="2">
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<p><EFBFBD> </font><font FACE="Times New Roman">Try doing terrain style texture
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mapping on non-terrain geometry. Results will definitely vary, but some could be
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interesting.</p>
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</blockquote>
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</blockquote>
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<b>
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<p>Samples:</b> The last height map and the alphamap used to create each of the
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terrain maps in Team Arena is included in the Mapping Support folder. Note that
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the designers made vertex manipulations to the final terrain meshes that are not
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reflected in these height maps. Also, the alphamaps are in PCX format, not BMP
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format.</p>
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</font>
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<p align="center"><a href="entity_keys_and_values.html">Back</a> - <a href="table_of_contents.html">Table
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of Contents</a> - <a href="terrain_texture.html">The Terrain Texture</a></p>
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<p> </td>
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</tr>
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</table>
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</div>
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</b>
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<p align="center"> </p>
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<p align="center"> </p>
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<p align="center">-16-</p>
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</body>
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</html>
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