CODEWITHSUNDEEP
c++opengl
Grav
Grav

Reputation: 491

Drawing a contiguous spiral?

Here's a function that I wrote that draws a spiral:

void drawSpiral(GLfloat x1, GLfloat y1, GLfloat radius)
{
    int lineAmount = 500;
    GLfloat piMultiplier = 10.0f * 3.141592654;

    glBegin(GL_LINES);

    for (int i = 0; i <= lineAmount; i++) 
    {
        GLfloat theta = i/lineAmount*piMultiplier;
        GLfloat x = x1 + (radius*cos(i*piMultiplier/lineAmount));
        GLfloat y = y1 + (radius*sin(i*piMultiplier/lineAmount));

        glVertex2f(x, y);

        radius += 1;
    }
    glEnd();
}

The problem is that the spiral gets drawn as dotted lines instead of one contiguous line.

spiral-lines

I can get a continuous line using GL_LINE_LOOP instead of GL_LINES, but that (understandably) draws a line from the middle to outside of the spiral. So I know my logic is good, I'm just not sure whats the opengl way of doing this.

Upvotes: 0

Views: 962

Answers (1)

arboreal84
arboreal84

Reputation: 2154

You can either do:

  • GL_LINES with an array of vertex like: [start, end, start, end...]. In this case, you would need a very redundant array like: [A, B, B, C, C, D]

  • GL_LINE_STRIP with an array of vertices like [A, B, C, D]

  • GL_LINE_LOOP will create a line between the final vertex and the first, I don't think that's what you want.

In short, use GL_LINE_STRIP rather than GL_LINES.

Upvotes: 4

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