CODEWITHSUNDEEP
c++windowsopenglglfwwavefront
viraj
viraj

Reputation: 1814

flickering while rendering a 3D object (.obj file) using OpenGL

While attempting to render a 3D object using OpenGL (and the GLFW library), the model experiences lots of flickering. Im reading the .obj file using a library that I've written on my own.

Written below is my render function: Unfortunately, in order to understand how faces and vertices are being inputted, I will have to provide all my code, which is linked: Zipped code along with executable and sample .obj: Source

Im using .obj files from here to test the program. Right now, the program doesn't support normals and textures, which isnt an issue since most of the models on the site dont have them. Also, (right now) it only reads from "123.obj" so the file should'nt be named anything else. And it only accepts a single space, not more than that.

 float render()
    {
        glfwSetTime(0.0f);
        int win_width;
        int win_height;
        glfwGetWindowSize(&win_width, &win_height);
        float win_aspect = (float)win_width / (float)win_height;
        glViewport(0, 0, win_width, win_height);

        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        gluPerspective(90, win_aspect, 0, 100.0);

        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();
        gluLookAt(0, 0, 50.0, 0, 0, 0, 0.0, 1.0, 0.0);

        glEnable(GL_DEPTH);
        glEnable(GL_DEPTH_TEST);
        glEnable(GL_COLOR_MATERIAL);
        glEnable(GL_NORMALIZE); 
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        glRotatef(angle , 0 , 1, 0);
        glColor3f(0.0f, 0.0f, 0.0f);
        int index = 0;
        for(int a = 0; a < faces.size(); a++)
        {
            if(faces[a].vertices.size() == 3)
            {
                glBegin(GL_TRIANGLES);
            }
            else
            {
                glBegin(GL_QUADS);
            }
            for(int b = 0; b < faces[a].vertices.size(); b++)
            {
                index = faces[a].vertices[b];
                glVertex3f(vertices[index].Dimensions[_x], vertices[index].Dimensions[_y], vertices[index].Dimensions[_z]);
            }
            glEnd();
        }
        glfwSwapBuffers();
        return (float)glfwGetTime();

Upvotes: 3

Views: 2839

Answers (1)

Hannesh
Hannesh

Reputation: 7488

Here's the problem

gluPerspective(90, win_aspect, 0, 100.0);

You cannot set 0 as your nearclip, set it to something larger like 0.1, or 1.0.

gluPerspective(90, win_aspect, 1.0, 100.0);

With nearclip at 0, all of your depths get mapped to z = 1, and you get z fighting.

EDIT : if you're interested, here's some theory on perspective depth:

For a given distance from the camera x, your perspective transform outputs a certian depth value z. At the farclip, this value will be the maximum of 1, and at nearclip it will be 0. Between these values however, relationship is not linear like you may expect. The curve looks similar to the following diagrams:

Diagram

When you go to the extreme of setting your nearclip to 0, your curve is heavily warped, so now all distances map to z = 1.

Because of all this, you should also try to keep the ratio far:near smaller than 10000:1

Upvotes: 7

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