OpenGL tessellation bug

Joseph_K_ — Sun, 30 Mar 2014 12:10:19 GMT

Platform: Windows 8.1 x64, MSVC 2010 x64, Intel HD4600 (4770K), driver version: 10.18.10.3496

The problem: I got shader linking error when linking a program using control and evaluation "Type mismatch: Type of gl_TessLevelInner different between shaders." If I comment out the line in ES where I read that value, whole program crashes (Access violation) when trying to bind this program via glBindProgram. Tested on several nV/AMD GPUs without any issues. However, other very simple tessellation program seems to work.

Control shader:

#version 400 compatibility

layout(vertices=1)out;

uniform vec4 LightPosition;

int GreaterVec(vec3 a,vec3 b){
return int(dot(sign(a-b),vec3(4,2,1)));
}
int ComputeMult(vec3 A,vec3 B,vec3 C,vec4 L){
vec3 n=cross(C-A,L.xyz-A*L.w);
return int(sign(dot(n,B-A)));
}
bool IsEdgeVisible(in vec4 A,in vec4 B){
   vec3 M=+A.xyz+A.www;
   vec3 N=+B.xyz+B.www;
   vec3 O=-A.xyz+A.www;
   vec3 P=-B.xyz+B.www;
   vec3 NM=N-M;
   vec3 PO=P-O;
   float Left=0;
   float Right=1;
   for(int i=0;i<3;++i){
       if(NM==0){
           if(M<0)return false;
       }else{
           if(NM>0)Left=max(Left,-M/NM);
           else Right=min(Right,-M/NM);
       }

       if(PO==0){
           if(O<0)return false;
       }else{
           if(PO>0)Left=max(Left,-O/PO);
           else Right=min(Right,-O/PO);
       }
   }
   return Left<=Right;
}

bool IsFullVisible(in vec4 A,in vec4 B,in vec4 C,int Diag){
vec3 a=A.xyz;
vec3 b=B.xyz;
vec3 c=C.xyz;
if(Diag>=0){
    a[Diag]=-a[Diag];
    b[Diag]=-b[Diag];
    c[Diag]=-c[Diag];
}
   float m=(a.x-a.y);
   float n=(b.x-b.y);
   float o=(c.x-c.y);
   float p=(a.x-a.z);
   float q=(b.x-b.z);
   float r=(c.x-c.z);
float d=(q*o-n*r);
float t=(m*r-p*o)/d;
float l=-(m*q-p*n)/d;
   vec4 X=A+t*B+l*C;
return (t>0)&&(t<1)&&(l>0)&&(l<1)&&
      all(greaterThan(X.xyz,-X.www))&&all(lessThan(X.xyz,X.www));
}

#define MATRIX gl_ModelViewProjectionMatrix
bool IsVisible(in vec4 a,in vec4 b,in vec4 c,in vec4 d,vec4 l){
   vec4 A=MATRIX*a;
   vec4 B=MATRIX*b;
   vec4 C=MATRIX*c;
   vec4 D=MATRIX*d;
   vec3 n=(MATRIX*vec4(cross(b.xyz-a.xyz,l.xyz-a.xyz*l.w),0)).xyz;
   ivec3 Corner=ivec3(1+sign(n))>>1;
if(Corner.z==1);Corner=ivec3(1)-Corner;
   int Diag=Corner.x+(Corner.y<<1)-1;
   if(IsFullVisible(A,B-A,C-A,Diag))return true;
   if(IsEdgeVisible(A,B))return true;
   if(IsEdgeVisible(A,C))return true;
   if(IsEdgeVisible(B,D))return true;
   if(IsEdgeVisible(C,D))return true;
   return false;
}

patch out vec4 P[4];

void main(){
int Num=int(gl_in[2].gl_Position.x);

int Multiplicity=0;
#define PLL LightPosition
#define PA gl_in[0].gl_Position
#define PB gl_in[1].gl_Position
#define PC vec4(gl_in[0].gl_Position.xyz*PLL.w-PLL.xyz,0)
#define PD vec4(gl_in[1].gl_Position.xyz*PLL.w-PLL.xyz,0)
if(!IsVisible(PA,PB,PC,PD,PLL))
{
gl_TessLevelOuter[1]=0;
gl_TessLevelOuter[0]=0;
gl_TessLevelOuter[3]=gl_TessLevelOuter[2]=0.0;
gl_TessLevelInner[1]=gl_TessLevelInner[0]=0.0;
return;
}
for(int i=0;i<Num;++i){
#define T0 gl_in[0].gl_Position.xyz
#define T1 gl_in[1].gl_Position.xyz
#define T2 gl_in[i+3].gl_Position.xyz
    if(GreaterVec(T0,T2)>0){//T[2] T[0] T[1]?
      Multiplicity+=ComputeMult(T2,T0,T1,LightPosition);
    }else{
      if(GreaterVec(T1,T2)>0){//T[0] T[2] T[1]?
        Multiplicity-=ComputeMult(T0,T2,T1,LightPosition);
      }else{//T[0] T[1] T[2]?
        Multiplicity+=ComputeMult(T0,T1,T2,LightPosition);
      }
    }
}

int AbsMultiplicity=abs(Multiplicity);
gl_TessLevelOuter[0]=int(AbsMultiplicity>0);
gl_TessLevelOuter[2]=1;
gl_TessLevelOuter[1]=gl_TessLevelOuter[3]=gl_TessLevelInner[0]=2*AbsMultiplicity-1;
gl_TessLevelInner[1]=1;

if(Multiplicity>0){
    P[0]=vec4(gl_in[1].gl_Position.xyz,1);
    P[1]=vec4(gl_in[0].gl_Position.xyz,1);
    P[2]=vec4(gl_in[1].gl_Position.xyz*LightPosition.w-LightPosition.xyz,0);
    P[3]=vec4(gl_in[0].gl_Position.xyz*LightPosition.w-LightPosition.xyz,0);
}
if(Multiplicity<0)
{
    P[0]=vec4(gl_in[0].gl_Position.xyz,1);
    P[1]=vec4(gl_in[1].gl_Position.xyz,1);
    P[2]=vec4(gl_in[0].gl_Position.xyz*LightPosition.w-LightPosition.xyz,0);
    P[3]=vec4(gl_in[1].gl_Position.xyz*LightPosition.w-LightPosition.xyz,0);
}
}

----------------------------

Evaluation shader:

#version 400 compatibility

layout(quads,fractional_odd_spacing,cw)in;

patch in vec4 P[4];

int GetIndex(){
int x=int(round(gl_TessCoord.x*gl_TessLevelInner[0]))*2;
int y=int(round(gl_TessCoord.y));
int id=x+y;
int l=((id+2)/4)%2;
int t=(id%2)^((id/4)%2);
return t+l*2;
}

void main(){
gl_Position=gl_ModelViewProjectionMatrix*P[GetIndex()];
}

---------------

A little mistake - it crashes

Joseph_K_ — Sun, 30 Mar 2014 12:20:24 GMT

A little mistake - it crashes on glUseProgram, not bind... (btw where is post edit button?)

Hi Joseph,

Michael_C_Intel2 — Wed, 02 Jul 2014 17:01:00 GMT

Hi Joseph,

Thanks for bring this to our attention. I have disucssed it with our OopenGL driver development team and they will investigate the issue. When I have an update I will let you know.

Hi Joseph,

Michael_C_Intel2 — Fri, 12 Sep 2014 21:35:11 GMT

Hi Joseph,

A new driver has been released that has a fix for your issue.

https://downloadcenter.intel.com/Detail_Desc.aspx?DwnldID=24245&lang=eng&ProdId=3720

topic A little mistake - it crashes in Developing Games on Intel Graphics

OpenGL tessellation bug

A little mistake - it crashes

Hi Joseph,

Hi Joseph,