140 lines
4.8 KiB
Plaintext
140 lines
4.8 KiB
Plaintext
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">
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<HTML>
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<META name="generator" content="HTML Tidy, see www.w3.org">
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<TITLE>Environment Mapping Tips</TITLE>
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<LINK type="text/css" rel="stylesheet" href="../webdocs.css">
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</HEAD>
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<BODY>
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<P><A href="intro.html">[Back to Intro]</A></P>
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<H1>Tips for Successful Environment Map Generation</H1>
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<P>Environment maps don't necessarily need to come from
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Anachronox environments. If you want to create your own
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environment map, some of these ramblings may come in handy.</P>
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<P>As you know, the parabolic environment map method uses two
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sources textures. It draws the entity in two passes, first with
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the front environment map, and then with the back environment
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map with a special alpha channel applied to it. The images
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below are a sample environment map, showing the alpha channel
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that Anachronox uses for the back image.</P>
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<TABLE summary="Parabolic Environment Textures with captions">
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<TR>
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<TH>front</TH>
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<TH>back</TH>
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</TR>
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<TR>
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<TD><IMG src="tips_map_ft.jpg" alt="Front Texture"></TD>
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<TD><IMG src="tips_map_bk.jpg" alt=
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"Back Texture with alpha"></TD>
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</TR>
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</TABLE>
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<P>Because it draws in two passes, and because we are only
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using per-vertex, not per-pixel, parabolic environment mapping,
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there is a seam visible around the circle of the back image. To
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better illustrate the seam, here are two example
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screenshots:</P>
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<TABLE summary="Normal Reflection Image with caption">
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<TR>
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<TH>normal</TH>
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</TR>
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<TR>
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<TD><IMG src="tips_reflect_1.jpg" alt="Normal Reflection">
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</TD>
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</TR>
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</TABLE>
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<P>And here is the same image with the back image colored
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green:</P>
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<TABLE summary="Seam Enhanced Reflection Image with caption">
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<TR>
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<TH>seam-enhanced</TH>
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</TR>
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<TR>
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<TD><IMG src="tips_reflect_2.jpg" alt=
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"Enhanced-seam Reflection"></TD>
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</TR>
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</TABLE>
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<P>As you can see, there is a seam that occurs along the edge
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of the circle of the alpha map of the back image (the seam also
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occurs in the same place in the front image), and it makes the
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horizon in our example look disjointed. Most of the time, this
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seam is not noticeable, especially on animating or rotating
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entities, but occasionally it can be a problem, especially on
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sharp and higher-resolution environment maps. An easy
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workaround is to use lower resolution environment maps and/or
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blur the image. However, it is the responsibility of the
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environment map artist to try and make sure that very sharp
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contrast elements do not occur across the seam, such as the
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sunlit horizon in this example. So far, we've been using an
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environment cube I generated from <B>map tensil</B>, here is
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the cube map laid out:</P>
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<TABLE>
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<TR>
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<TH>Tensil Cube Map Layout</TH>
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</TR>
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<TR>
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<TD><IMG src="cubemap-tensil.gif" alt="Tensil Cube Map">
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</TD>
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</TR>
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</TABLE>
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<P>And here is a visualization of how the seam results from
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dual parabolic mapping (click on the image to view the
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movie):</P>
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<TABLE>
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<TR>
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<TH>Parabolic Seam Visualization</TH>
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</TR>
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<TR>
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<TD><A href="joeyparab2.m1v"><IMG src="tips_seam.jpg" alt=
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"Parabolic Seam Visualization"></A></TD>
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</TR>
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</TABLE>
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<P>The x axis is red, the y axis is green, the z axis is blue,
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and the pink dividing square shows the plane along which the
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seam occurs. When you are creating environment maps from
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scratch, it is best to avoid details that cross the seam which
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is along the Y-Z plane as shown above. One technique is to
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rotate the base camera position for the cube map generation in
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your 3D package.</P>
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<P>Unfortunately, this technique cannot apply to screenshots
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taken within Anachronox. When Anachronox takes a set of
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cube-environment screenshots, it will always position the 6
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textures in the manner shown above. The first image is out on
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the positive x axis, the second image is on the positive y
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axis, and so forth. Initial camera rotation has no bearing on
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the output, only camera position. The workarounds including
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trying to position the camera for the screenshots to minimize
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the seam problem, or to heavily blur and use lower resolution
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textures so details are not apparent along the seam.</P>
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<P>Please send any comments, suggestions, or more tips to
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Joey.</P>
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<P><A href="intro.html">[Back to Intro]</A></P>
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