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Speckles on models at far distances


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#1 Shawn619   Members   -  Reputation: 342

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Posted 11 June 2013 - 12:00 PM

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?

 

2wdn81l.jpg



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#2 radioteeth   Prime Members   -  Reputation: 1054

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Posted 11 June 2013 - 10:55 PM

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?



#3 Shawn619   Members   -  Reputation: 342

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Posted 12 June 2013 - 12:05 AM

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:

	
	int loadObject(const char* filename)
	
	
	{
	
	
	        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++)
	
	
	        {
	
	
	                if(faces[i]->four)      //if it's a quad draw a quad
	
	
	                {
	
	
	                        glBegin(GL_QUADS);
	
	
	                                //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
	
	
	}
	















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




Edited by Shawn619, 12 June 2013 - 12:15 AM.


#4 marcClintDion   Members   -  Reputation: 431

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Posted 12 June 2013 - 11:17 AM

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.


Consider it pure joy, my brothers and sisters, whenever you face trials of many kinds, because you know that the testing of your faith produces perseverance. Let perseverance finish its work so that you may be mature and complete, not lacking anything.


#5 Shawn619   Members   -  Reputation: 342

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Posted 12 June 2013 - 02:40 PM

My drawing goes like this:

//globals
GLuint shaderOne;
 
//init
shaderOne = initializeShader(...)
//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);
glLoadIdentity();
gluPerspective(60.0, (float)windowWidth / (float)windowHeight, 0.4, 9000.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
 
 
 
//enables/disables
glEnable(GL_DEPTH_TEST);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
 
 
//start shader
glUseProgram(shaderOne);
 
 
//set camera
gluLookAt(cam.posX,cam.posY,cam.posZ,cam.viewX,cam.viewY,cam.viewZ,cam.upX,cam.upY,cam.upZ);
 
//draw calls
//...
 
 
//end shader
glUseProgram(0);


glutSwapBuffers();

//end drawing per frame








Edited by Shawn619, 12 June 2013 - 02:41 PM.


#6 Shawn619   Members   -  Reputation: 342

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Posted 17 June 2013 - 10:25 PM

Any ideas?



#7 Shawn619   Members   -  Reputation: 342

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Posted 18 June 2013 - 02:28 PM

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.

 

Here is the result(with smooth instead of flat shading):

263jyoy.jpg


Edited by Shawn619, 18 June 2013 - 02:29 PM.





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