how to draw a spiral using opengl - opengl

Question

I want to know how to draw a spiral.
I wrote this code:
void RenderScene(void)
{
glClear(GL_COLOR_BUFFER_BIT);
GLfloat x,y,z = -50,angle;
glBegin(GL_POINTS);
for(angle = 0; angle < 360; angle += 1)
{
x = 50 * cos(angle);
y = 50 * sin(angle);
glVertex3f(x,y,z);
z+=1;
}
glEnd();
glutSwapBuffers();
}
If I don't include the z terms I get a perfect circle but when I include z, then I get 3 dots that's it. What might have happened?
I set the viewport using glviewport(0,0,w,h)
To include z should i do anything to set viewport in z direction?

Answer 1

You see points because you are drawing points with glBegin(GL_POINTS).
Try replacing it by glBegin(GL_LINE_STRIP).
NOTE: when you saw the circle you also drew only points, but drawn close enough to appear as a connected circle.
Also, you may have not setup the depth buffer to accept values in the range z = [-50, 310] that you use. These arguments should be provided as zNear and zFar clipping planes in your gluPerspective, glOrtho() or glFrustum() call.
NOTE: this would explain why with z value you only see a few points: the other points are clipped because they are outside the z-buffer range.
UPDATE AFTER YOU HAVE SHOWN YOUR CODE:
glOrtho(-100*aspectratio,100*aspectratio,-100,100,1,-1); would only allow z-values in the [-1, 1] range, which is why only the three points with z = -1, z = 0 and z = 1 will be drawn (thus 3 points).
Finally, you're probably viewing the spiral from the top, looking directly in the direction of the rotation axis. If you are not using a perspective projection (but an isometric one), the spiral will still show up as a circle. You might want to change your view with gluLookAt().
EXAMPLE OF SETTING UP PERSPECTIVE
The following code is taken from the excellent OpenGL tutorials by NeHe:
glViewport(0, 0, width, height);
glMatrixMode(GL_PROJECTION); // Select The Projection Matrix
glLoadIdentity(); // Reset The Projection Matrix
// Calculate The Aspect Ratio Of The Window
gluPerspective(45.0f,(GLfloat)width/(GLfloat)height,0.1f,100.0f);
glMatrixMode(GL_MODELVIEW); // Select The Modelview Matrix
glLoadIdentity(); // Reset The Modelview Matrix
Then, in your draw loop would look something like this:
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear The Screen And The Depth Buffer
glLoadIdentity();
glTranslatef(-1.5f,0.0f,-6.0f); // Move Left 1.5 Units And Into The Screen 6.0
glBegin(GL_TRIANGLES); // Drawing Using Triangles
glVertex3f( 0.0f, 1.0f, 0.0f); // Top
glVertex3f(-1.0f,-1.0f, 0.0f); // Bottom Left
glVertex3f( 1.0f,-1.0f, 0.0f); // Bottom Right
glEnd();
Of course, you should alter this example code your needs.

Answer 2

catchmeifyoutry provides a perfectly capable method, but will not draw a spatially accurate 3D spiral, as any render call using a GL_LINE primitive type will rasterize to fixed pixel width. This means that as you change your perspective / view, the lines will not change width. In order to accomplish this, use a geometry shader in combination with GL_LINE_STRIP_ADJACENCY to create 3D geometry that can be rasterized like any other 3D geometry. (This does require that you use the post fixed-function pipeline however)
I recommended you to try catchmeifyoutry's method first as it will be much simpler. If you are not satisfied, try the method I described. You can use the following post as guidance:
http://prideout.net/blog/?tag=opengl-tron

Answer 3

Here is my Spiral function in C. The points are saved into a list which can be easily drawn by OpenGL (e.g. connect adjacent points in list with GL_LINES).
cx,cy ... spiral centre x and y coordinates
r ... max spiral radius
num_segments ... number of segments the spiral will have
SOME_LIST* UniformSpiralPoints(float cx, float cy, float r, int num_segments)
{
SOME_LIST *sl = newSomeList();
int i;
for(i = 0; i < num_segments; i++)
{
float theta = 2.0f * 3.1415926f * i / num_segments; //the current angle
float x = (r/num_segments)*i * cosf(theta); //the x component
float y = (r/num_segments)*i * sinf(theta); //the y component
//add (x + cx, y + cy) to list sl
}
return sl;
}
An example image with r = 1, num_segments = 1024:
P.S. There is difference in using cos(double) and cosf(float).
You use a float variable for a double function cos.