Difference between revisions of "Azurik: Rise of Perathia"
From xboxdevwiki
(Temporary hack) |
|||
| Line 3: | Line 3: | ||
==== 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. |
[[File:http://i.imgur.com/tpmLpjP.png]] | [[File:http://i.imgur.com/tpmLpjP.png]] | ||
| Line 22: | Line 22: | ||
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 | |
Revision as of 13:37, 29 March 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.
File:Http://i.imgur.com/tpmLpjP.png
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
