文件列表:

unified_lod_2 (0, 2003-03-19)
unified_lod_2\app_shell (0, 2003-03-19)
unified_lod_2\app_shell\app_shell.cpp (24322, 2003-03-18)
unified_lod_2\app_shell\app_shell.h (2288, 2003-03-13)
unified_lod_2\app_shell\glext.h (12284, 2002-09-27)
unified_lod_2\app_shell\include (0, 2003-03-15)
unified_lod_2\app_shell\include\jconfig.h (1378, 2002-05-08)
unified_lod_2\app_shell\include\jmorecfg.h (12821, 2002-05-08)
unified_lod_2\app_shell\include\jpeglib.h (47301, 2002-05-08)
unified_lod_2\app_shell\include\zconf.h (8133, 2002-05-08)
unified_lod_2\app_shell\include\zlib.h (41791, 2002-05-08)
unified_lod_2\app_shell\jpeg_load.cpp (2148, 2002-05-08)
unified_lod_2\app_shell\jpeg_load.h (132, 2002-05-08)
unified_lod_2\app_shell\lib (0, 2003-03-15)
unified_lod_2\app_shell\lib\jpg.lib (289384, 2002-05-08)
unified_lod_2\app_shell\lib\zlib.lib (81568, 2002-05-08)
unified_lod_2\app_shell\os_specific_opengl_headers.h (219, 2003-03-12)
unified_lod_2\binary_file_stuff.h (3915, 2003-02-16)
unified_lod_2\bt_loader.cpp (2439, 2003-02-16)
unified_lod_2\bt_loader.h (133, 2002-12-09)
unified_lod_2\Copyright.txt (491, 2003-03-14)
unified_lod_2\data (0, 2003-03-19)
unified_lod_2\data\bitmaps (0, 2003-03-18)
unified_lod_2\data\bitmaps\3grass001.jpg (16595, 2003-03-13)
unified_lod_2\data\bitmaps\white.jpg (5582, 2003-03-18)
unified_lod_2\data\bt_files (0, 2003-03-15)
unified_lod_2\data\bt_files\crater_0513.bt (1052932, 2000-12-23)
unified_lod_2\data\Century Big.font_map (2657, 2002-09-27)
unified_lod_2\data\Century Big.jpg (48930, 2002-09-27)
unified_lod_2\data\Century Small.font_map (2657, 2002-09-27)
unified_lod_2\data\Century Small.jpg (32862, 2002-09-27)
unified_lod_2\data\crater_0513.terrain_tree (27027339, 2003-03-19)
unified_lod_2\data\test_bumps_small.terrain_tree (1107217, 2003-03-14)
unified_lod_2\framework (0, 2003-03-19)
unified_lod_2\framework.h (1835, 2003-03-19)
unified_lod_2\framework\auto_array.cpp (868, 2003-03-12)
unified_lod_2\framework\auto_array.h (3313, 2003-02-16)
unified_lod_2\framework\bit_array.cpp (629, 2003-02-19)
unified_lod_2\framework\bit_array.h (1316, 2002-06-11)
unified_lod_2\framework\data_structures.cpp (1006, 2003-03-03)
... ...

Okay, here we are with the second installment of this environmental LOD series, "unified_lod_2". If you didn't download and look at "unified_lod_1" first, you might want to do that, since it is a little bit simpler. This month the code drops you straight into terrain rendering mode. All the keyboard commands are documented on-screen. The main difference between this month's code and last month's is that alpha blending is now being used to eliminate popping. However, there are some other minor differences -- the file format is slightly different, for example. So the two demos don't interoperate. I did some refactoring of this code after writing the corresponding article. Mainly, I changed the order in which things are drawn. Now the solid version of each block in the terrain is drawn first; then in a second pass the transitioning blocks get mixed into the final image. If you want to see the alpha-blending work very clearly, then hit 'S' to turn off the rendering of solid blocks. This will also show you how much fill-rate overhead there is in the blending step; and really, there isn't all that much. I think in the article I might have given the impression that a lot of extra fill was required (an impression aided by the fact that there was a layout error in the article, and the wrong image was given in one of the figures, so it looks like more pixels are being filled than actually are). Don't pay too much attention to the frame rate yet, since absolutely no optimization has been done (and the system will still change significantly before it is complete). [Below are some notes pasted from unified_lod_1, but which are just as relevant here]: Even though the terrain is rendered as static blocks, I am not using vertex buffers for them. Right now I am rendering them in pretty much the slowest possible way, i.e. calling glVertex() a bunch of times. You could fix this pretty easily, but I figure I will wait until the final version before doing low-level performance tweaks like that. The important thing to remember is that because they are static blocks, they *can* be rendered very efficiently as vertex buffers should we choose to do so. The way I output vertex normals may confuse some people. You'll see that I don't store a surface normal at every vertex in the mesh data structure; instead, I store a tangent frame, represented as a quaternion. This quaternion contains all the information you need to compute the normal, tangent, and binormal vectors. I use quaternions because they are small, they are nice to interpolate, and they can be used directly in high-end shaders to produce anisotropic lighting effects. For now though, because we're only doing DX8-level stuff, I extract the vertex normal manually, by rotating the Z-axis (0, 0, 1) by the quaternion. This is not very fast as I've implemented it, but you can make it much faster using a specialized function made to extract the rotated Z-axis from a quaternion. I talk about the math behind this in my Game Developer article "Inverse Kinematics with Joint Limits" [basically, write out the algebra for (q)z(q*) and simplify]. I will probably make this upgrade for next month's code. I have included a utility "preprocess_terrain" that generates .terrain_tree files. If you run it with no arguments, it will generate a simple sine-wave terrain. If you give it the name of a .bt file as an argument, it will parse that .bt file and preprocess it appropriately. For more information on the .bt file format, see http://vterrain.org. I have supplied the original .bt file for the Crater Lake map in case you want to make changes to the preprocessor or mesh format. All this data made the download pretty large; sorry about that. At some point maybe I will do an article about mesh compression. (Quaternions as tangent frames compress very nicely, I'll have you know!) I originally wrote this code in my personal game engine. To port this into an OpenGL-based open source app, I extracted some of my game engine source, simplified it some, and put it in the subdirectories 'framework' and 'mesh'. 'framework' is basically all supporting code that doesn't have much to do with the basic algorithm. 'mesh' is supporting code that *does* have to do with the basic algorithm (for example, it contains the mesh simplification code). Because Windows XP has lousy scheduling, the frame rate in this app is a bit skippy sometimes under XP. I don't know how to fix this without doing relatively convoluted and disgusting things that have no place in a demo... so we get to live with that. Windows XP ... 10 millisecond timeslices, my ass. Jonathan Blow March 19, 2003 Bouldin Creek Cafe in Austin, Texas

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