Difference between revisions of "Azurik: Rise of Perathia"
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=== Known tricky behaviour === | === Known tricky behaviour === | ||
==== Skinning code / Shader rounding mode ==== | ==== Skinning code / Shader rounding mode ==== | ||
| − | This game suffers from issues with non-exact rounding in the shaders which do the skinning / skeletal animation. | + | This game depends on correct GPU rounding. If an emulator suffers from issues with non-exact rounding in the shaders which do the skinning / skeletal animation the character models will be very broken. |
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| + | [[File:Azurik--Rise-of-Perathia--bugged.png]] | ||
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IIRC Code is like: | IIRC Code is like: | ||
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A0 = 765 * raw/255 = 3*raw. | A0 = 765 * raw/255 = 3*raw. | ||
| − | This should all be working, but it's not. NV2A | + | This should all be working, but it's not. [[NV2A/Vertex Shader]] does round-to-zero. Behaviour for GLSL and other modern graphic APIs is undefined.. |
| − | + | To work around this rounding issue <code>A0 += 1.0/255.0</code> can be used as a temporary hack | |
Latest revision as of 03:17, 27 June 2017
Known tricky behaviour
Skinning code / Shader rounding mode
This game depends on correct GPU rounding. If an emulator suffers from issues with non-exact rounding in the shaders which do the skinning / skeletal animation the character models will be very broken.
IIRC Code is like:
A0 = c[113].x + c[113].z = 18 *do stuff with c[96+A0] to c[98+A0]* A0 = c[113].x + c[113].z = 21 *do stuff with c[96+A0] to c[98+A0]* A0 = c[113].y * v2 *do stuff with c[96+A0] to c[98+A0]* c[113] is vec4(15, 765, 3, 0). 765 = 3*255. v2 is GL_UNSIGNED_BYTE, normalized => v2 = raw/255. A0 = 765 * raw/255 = 3*raw.
This should all be working, but it's not. NV2A/Vertex Shader does round-to-zero. Behaviour for GLSL and other modern graphic APIs is undefined..
To work around this rounding issue A0 += 1.0/255.0 can be used as a temporary hack
