# OpenGL Speckles on models at far distances

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I get these weird speckles on my model when using a shader and rendering the model at far distances. You can see this if you look closely at the triangles rendered closer to the sun(light) and triangles render further from the sun. Anyone know what this phenomena is called? And possible how to fix it in opengl?

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Maybe z-fighting? How is your geometry organized? How are you generating it? What is the 'box' around everything?...and lastly, out of sheer curiousity, why is everything green?

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Maybe z-fighting? How is your geometry organized? How are you generating it? What is the 'box' around everything?...and lastly, out of sheer curiousity, why is everything green?

There's nothing technical behind coloring everything green. Green is supposed to represent a forest terrain, it reminds me of final fantasy, specifically ff tactics.

But I import all models through a .obj importer that is like this one, except I changed it to save all verts,normals,faces and not discards them after saving the model to a display list, then wrapped it in a class:



{

std::vector<std::string*> coord;        //read every single line of the obj file as a string

std::vector<coordinate*> vertex;

std::vector<face*> faces;

std::vector<coordinate*> normals;       //normal vectors for every face

std::ifstream in(filename);     //open the .obj file

if(!in.is_open())       //if not opened, exit with -1

{

std::cout << "Nor oepened" << std::endl;

return -1;

}

char buf[256];

//read in every line to coord

while(!in.eof())

{

in.getline(buf,256);

coord.push_back(new std::string(buf));

}

//go through all of the elements of coord, and decide what kind of element is that

for(int i=0;i<coord.size();i++)

{

if(coord[i]->c_str()[0]=='#')   //if it is a comment (the first character is #)

continue;       //we don't care about that

else if(coord[i]->c_str()[0]=='v' && coord[i]->c_str()[1]==' ') //if vector

{

float tmpx,tmpy,tmpz;

sscanf(coord[i]->c_str(),"v %f %f %f",&tmpx,&tmpy,&tmpz);       //read in the 3 float coordinate to tmpx,tmpy,tmpz

vertex.push_back(new coordinate(tmpx,tmpy,tmpz));       //and then add it to the end of our vertex list

}else if(coord[i]->c_str()[0]=='v' && coord[i]->c_str()[1]=='n')        //if normal vector

{

float tmpx,tmpy,tmpz;   //do the same thing

sscanf(coord[i]->c_str(),"vn %f %f %f",&tmpx,&tmpy,&tmpz);

normals.push_back(new coordinate(tmpx,tmpy,tmpz));

}else if(coord[i]->c_str()[0]=='f')     //if face

{

int a,b,c,d,e;

if(count(coord[i]->begin(),coord[i]->end(),' ')==3)     //if it is a triangle (it has 3 space in it)

{

sscanf(coord[i]->c_str(),"f %d//%d %d//%d %d//%d",&a,&b,&c,&b,&d,&b);

faces.push_back(new face(b,a,c,d));     //read in, and add to the end of the face list

}else{

sscanf(coord[i]->c_str(),"f %d//%d %d//%d %d//%d %d//%d",&a,&b,&c,&b,&d,&b,&e,&b);

faces.push_back(new face(b,a,c,d,e));   //do the same, except we call another constructor, and we use different pattern

}

}

}

//raw

int num;        //the id for the list

num=glGenLists(1);      //generate a uniqe

glNewList(num,GL_COMPILE);      //and create it

for(int i=0;i<faces.size();i++)

{

{

//basically all I do here, is use the facenum (so the number of the face) as an index for the normal, so the 1st normal owe to the first face

//I subtract 1 because the index start from 0 in C++

glNormal3f(normals[faces[i]->facenum-1]->x,normals[faces[i]->facenum-1]->y,normals[faces[i]->facenum-1]->z);

//draw the faces

glVertex3f(vertex[faces[i]->faces[0]-1]->x,vertex[faces[i]->faces[0]-1]->y,vertex[faces[i]->faces[0]-1]->z);

glVertex3f(vertex[faces[i]->faces[1]-1]->x,vertex[faces[i]->faces[1]-1]->y,vertex[faces[i]->faces[1]-1]->z);

glVertex3f(vertex[faces[i]->faces[2]-1]->x,vertex[faces[i]->faces[2]-1]->y,vertex[faces[i]->faces[2]-1]->z);

glVertex3f(vertex[faces[i]->faces[3]-1]->x,vertex[faces[i]->faces[3]-1]->y,vertex[faces[i]->faces[3]-1]->z);

glEnd();

}else{

glBegin(GL_TRIANGLES);

glNormal3f(normals[faces[i]->facenum-1]->x,normals[faces[i]->facenum-1]->y,normals[faces[i]->facenum-1]->z);

glVertex3f(vertex[faces[i]->faces[0]-1]->x,vertex[faces[i]->faces[0]-1]->y,vertex[faces[i]->faces[0]-1]->z);

glVertex3f(vertex[faces[i]->faces[1]-1]->x,vertex[faces[i]->faces[1]-1]->y,vertex[faces[i]->faces[1]-1]->z);

glVertex3f(vertex[faces[i]->faces[2]-1]->x,vertex[faces[i]->faces[2]-1]->y,vertex[faces[i]->faces[2]-1]->z);

glEnd();

}

}

glEndList();

//delete everything to avoid memory leaks

for(int i=0;i<coord.size();i++)

delete coord[i];

for(int i=0;i<faces.size();i++)

delete faces[i];

for(int i=0;i<normals.size();i++)

delete normals[i];

for(int i=0;i<vertex.size();i++)

delete vertex[i];

return num;     //return with the id

}



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The green box is just a couple of plain quads that house my scene.

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Edited by Shawn619

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There's not enough info to go on. Are you using a shader? If so, did you remember to make sure everything is intialized first? It could be that the geometry is duplicated and this would cause the z-fighting artifacts that radioteeth mentioned.

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My drawing goes like this:

//globals

//init
//end init

//drawing per frame

//draw scene
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glViewport(0, 0, windowWidth, windowHeight);
glClearColor(0,0.5,0.5,0);
glMatrixMode(GL_PROJECTION);
gluPerspective(60.0, (float)windowWidth / (float)windowHeight, 0.4, 9000.0);
glMatrixMode(GL_MODELVIEW);

//enables/disables
glEnable(GL_DEPTH_TEST);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

//set camera
gluLookAt(cam.posX,cam.posY,cam.posZ,cam.viewX,cam.viewY,cam.viewZ,cam.upX,cam.upY,cam.upZ);

//draw calls
//...

glUseProgram(0);

glutSwapBuffers();

//end drawing per frame


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Edited by Shawn619

Any ideas?

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Solved!

Very unusual problem, which is why I couldn't fine many similar problem on google.

I narrowed the problem down to the attenuation calculated in my glsl shader. Funnily enough, my attenuation calculations were fine. The problem was solved by changing:

if( gl_FrontFacing ){
//color = ambient and diffuse with attenuation
}else{
//color = only ambient
}



to

if( diffuseTerm > 0.0){
//color = ambient and diffuse with attenuation
}else{
//color = only ambient
}


I don't know how, but there was a problem with gl_FrontFacing.

Edited by Shawn619

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