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IshaqKassam
IshaqKassam

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Drawing a Circle using OpenGL - glfw/glew c++

#cpp #opengl #glfw #glew

Hoping that you have already setup glfw & glew, and are ready to learn how to draw 2D shapes, let's dive straight into this. In this article we are going to learn how to draw a circle in openGL using glfw, c++ language.

Here is the code:

 void drawCircle(float cx, float cy, float r, int num_segments) { float theta = 3.1415926 * 2 / float(num_segments); float tangetial_factor = tanf(theta);//calculate the tangential factor float radial_factor = cosf(theta);//calculate the radial factor float x = r;//we start at angle = 0 float y = 0; glLineWidth(2); glBegin(GL_LINE_LOOP); for (int ii = 0; ii < num_segments; ii++) { glVertex2f(x + cx, y + cy);//output vertex //calculate the tangential vector //remember, the radial vector is (x, y) //to get the tangential vector we flip those coordinates and negate one of them float tx = -y; float ty = x; //add the tangential vector x += tx * tangetial_factor; y += ty * tangetial_factor; //correct using the radial factor x *= radial_factor; y *= radial_factor; } glEnd(); }
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The function above can then be called in the main() function as such:

drawCircle(250, 250, 100, 360);
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To change the circle color, you can use the glColor3f() method which takes in 3 parameters, for the RGB values.

Add this line before calling the drawCircle function

glColor3f(0.0, 0.5, 0.5);
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