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Skinning Artifacts
http://horde3d.org/forums/viewtopic.php?f=2&t=1602		 Page 1 of 1
Author:  dazza007 [ 02.12.2011, 14:04 ]
Post subject:  Skinning Artifacts
Hi All,
Struck a few issues with Skinned characters.
Hoping someone can look at the below image - and tell me what I am doing wrong
The shadow mapping is all wrong when using the skinned flag, when i dont use it - the shadows are fine

Image

Cheers
Darrin
Author:  dazza007 [ 07.12.2011, 23:51 ]
Post subject:  Re: Skinning Artifacts
Well still no luck - however I have discovered something weird
- When the character is at world coordinates (0,0,0) and the camera not far off - everything looks fine
- the further the character gets away from 0,0,0 the worse the artifacting appears, you can actually see it degrade as you walk the character further away.
- it only appears to happen with shadow maps

- Any ideas, anyone? this has taken far too much time to try and isolate.

Cheers
D
Author:  worstplayer [ 31.05.2012, 19:14 ]
Post subject:  Re: Skinning Artifacts
Hello, I have same exact problem.

http://www.youtube.com/watch?v=Db4b6jw-1UI

Shadows appear OK when near the origin and get progressively more "screwy" as i move away.
This happens even when I don't move any bones, just adding skin flag is enough to trigger this.

EDIT: this is what gbuffer looks like: http://imgur.com/EpE6V

So, skinning outputs "wrong" position, and yet somehow the model is not visually distorted (but it affects lighting). I have absolutely no idea what's going on :shock: .

EDIT2: everything seems to work OK when the model has only one bone.
Author:  worstplayer [ 02.06.2012, 18:59 ]
Post subject:  Re: Skinning Artifacts
PROGRESS!

If I put this in the vertex shader:
Code:
pos.w=1.0;
gl_Position =viewProjMat *normalize( pos);
visual distortion exactly follows distortion in g-buffer position
Image

So, quick and dirty workaround would be putting this somewhere into VS_GENERAL and VS_SHADOWMAP:
Code:
pos.xyz/=pos.w;
pos.w=1.0;
This works well enough but i'm sure there's a better way to solve this.
Author:  MistaED [ 03.06.2012, 10:04 ]
Post subject:  Re: Skinning Artifacts
Ok here's the VS_SHADOWMAP pass:
Code:
[[VS_SHADOWMAP]]
// =================================================================================================
   
#include "shaders/utilityLib/vertCommon.glsl"
#include "shaders/utilityLib/vertSkinning.glsl"

uniform mat4 viewProjMat;
uniform vec4 lightPos;
attribute vec3 vertPos;
varying vec3 lightVec;

#ifdef _F05_AlphaTest
   attribute vec2 texCoords0;
   varying vec2 texCoords;
#endif

void main( void )
{
#ifdef _F01_Skinning   
   vec4 pos = calcWorldPos( skinPos( vec4( vertPos, 1.0 ) ) );
#else
   vec4 pos = calcWorldPos( vec4( vertPos, 1.0 ) );
#endif

#ifdef _F05_AlphaTest
   texCoords = texCoords0;
#endif

   lightVec = lightPos.xyz - pos.xyz;
   gl_Position = viewProjMat * pos;
}

Change it to look like:
Code:
[[VS_SHADOWMAP]]
// =================================================================================================
   
#include "shaders/utilityLib/vertCommon.glsl"
#include "shaders/utilityLib/vertSkinning.glsl"

uniform mat4 viewProjMat;
uniform vec4 lightPos;
attribute vec3 vertPos;
varying vec3 lightVec;

#ifdef _F05_AlphaTest
   attribute vec2 texCoords0;
   varying vec2 texCoords;
#endif

void main( void )
{
#ifdef _F01_Skinning
   mat4 skinningMat = calcSkinningMat();
   vec4 pos = calcWorldPos( skinPos( vec4( vertPos, 1.0 ), skinningMat ) );
#else
   vec4 pos = calcWorldPos( vec4( vertPos, 1.0 ) );
#endif

#ifdef _F05_AlphaTest
   texCoords = texCoords0;
#endif

   lightVec = lightPos.xyz - pos.xyz;
   gl_Position = viewProjMat * pos;
}

Does that fix the issue?
Author:  worstplayer [ 03.06.2012, 12:10 ]
Post subject:  Re: Skinning Artifacts
It didn't fix it by itself. The problem isn't only in VS_SHADOWMAP, but also in VS_GENERAL. In case of deferred lighting it puts wrong position into gbuffer.

The problem seems to come from vertSkinning.glsl, from this function:
Code:
vec4 skinPos( const vec4 pos, const mat4 skinningMat )
{
   return pos * skinningMat;
}


changing it to:
Code:
vec4 skinPos( const vec4 pos, const mat4 skinningMat )
{
   vec4 npos = pos * skinningMat;
   return vec4(npos.xyz/npos.w,1.0);
}

together with your change to VS_SHADOWMAP, finally made both casting and receiving shadows correct. Now, i don't understand exact mechanism of what's going on, but it seems that with skinning, pos.w isn't always exactly 1, so gl_Position=viewProjMat*pos still computes correct position, but things like lightVec=lightPos.xyz-pos.xyz don't.

EDIT: works in game http://www.youtube.com/watch?v=q99euNflHos , also going to test it with chicago guy and some other models.
EDIT2: Everything else works too.
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