No shape display pyopengl

February 20, 2022

So i’m trying to make a function for displaying a circle, here’s the function :

def drawCircle(x,y,size):
    glColor3f(1,1,1)
    glBegin(GL_TRIANGLE_STRIP)
    glVertex2f(0,0)
    glVertex2f(100,0)
    glVertex2f(100,100)
    glVertex2f(0,100)

But when i try it, nothing display. If you have the solution, please explain me in detail, I’m not a profesional in opengl or in pyopengl.

Here’s the code :

import glfw
from OpenGL.GL import *
from OpenGL.GLUT import *
import numpy as np
import pyrr
from random import *
from math import *

buffer = bytearray(800 * 600 * 3)
display = (800,600)

if not glfw.init():
    raise Exception("glfw can not be initialized!")

def CreateWindow(title="Baguette game",width=800,height=600):
    display = (width,height)
    window = glfw.create_window(width,height,title, None, None)
    glfw.set_window_pos(window,400,200)
    glfw.make_context_current(window)

    return window

def DrawTriangle(pointA=[-0.5, -0.5, 0.0],pointB=[0.5, -0.5,0.0],
                 pointC=[-0.5, 0, 0.0],color=[1.0,1.0,1.0]):
    vertices = [pointA[0], pointA[1], pointA[2],
                pointB[0], pointB[1], pointB[2],
                pointC[0], pointC[1], pointC[2]]

    colors = [color[0], color[1], color[2],
              color[0], color[1], color[2],
              color[0], color[1], color[2] ]
    
    v = np.array(vertices,dtype=np.float32)
    c = np.array(colors, dtype=np.float32)
    
    glEnableClientState(GL_VERTEX_ARRAY)
    glVertexPointer(3, GL_FLOAT,0,v)
    glEnableClientState(GL_COLOR_ARRAY)
    glColorPointer(3, GL_FLOAT,0,c)
    glDrawArrays(GL_TRIANGLES,0,3)

def DrawRectangle(size=[0.5,0.5],position=[0,0],color=[1.0,1.0,1.0]):
    DrawTriangle([position[0]-size[0]/2,position[1]+size[1]/2,0],
                  [position[0]+size[0]/2,position[1]+size[1]/2,0],
                  [position[0]+size[0]/2,position[1]-size[1]/2,0],
                  color)
    DrawTriangle([position[0]-size[0]/2,position[1]-size[1]/2,0],
                  [position[0]+size[0]/2,position[1]-size[1]/2,0],
                  [position[0]-size[0]/2,position[1]+size[1]/2,0],
                  color)

def Pixel(x,y):
    buffer_data = [randint(0,255), 0, 0] * (x * y)
    buffer = (GLubyte * (x * y * 3))(*buffer_data)
    glDrawPixels(x, y, GL_RGB, GL_UNSIGNED_BYTE, buffer)

def drawCircle(x,y,size):
    glColor3f(1,1,1)
    glBegin(GL_TRIANGLE_STRIP)
    glVertex2f(0,0)
    glVertex2f(100,0)
    glVertex2f(100,100)
    glVertex2f(0,100)
    
if __name__=="__main__":
    window = CreateWindow()
    initialPosition = (0,0,0)
    z=1
    while not glfw.window_should_close(window):
        glfw.poll_events()
        #glClear(GL_COLOR_BUFFER_BIT)

        DrawRectangle([1,1],[-0.5,0],[1,0,0])
        DrawRectangle([1,1],[0.5,0],[0,1,0])
        
        glfw.swap_buffers(window)
    glfw.terminate()

>Solution :

You don’t use the x, y and size arguments at all. A glBegin/glEnd sequence must be delimited with glEnd. e.g.:

def drawCircle(cx, cy, radius):
    glColor3f(1,1,1)
    glBegin(GL_TRIANGLE_FAN)
    glVertex2f(cx, cy)
    for a in range(361):
        x = cx + radius * cos(radians(a))
        y = cy + radius * sin(radians(a))
        glVertex2f(x, y)
    glEnd()

For example draw a circle in the center of the viewport: