OpenGL 3: Circle

This time, OpenGL is used to draw a circle, and a solid pentagram is drawn in the middle.

1. Draw solid five corners:

Since the previous use of polygen painting will fail, maybe the GPU hardware will be different, so the use of polygen to draw a solid five-pointed star is not reliable;

Therefore, polygen is not required to draw a star using a triangle.

2 circles

Because there is no circular shape in glew, we can only manually set the vertex and then draw the circle;

When the mathematical principles can be taken here: http://slabode.exofire.net/circle_draw.shtml

The final result is as follows:

Very beautiful, very standard star plus a circle.

Note: This program only uses vertex buffer and does not use index buffer.

#pragma once#include <stdio.h>#include <GL\glew.h>#include <GL\freeglut.h>#include "math_3d.h"#include <cmath>namespace Tutorial2_Tri_pentagram{GLuint VBO;const static float PI = 3.1415926f;const static double toPI = PI/180.0;const static double penR = 0.8;const static double penInR = penR * sin(18.0*toPI) / sin(126.0*toPI);void DrawCircle(Vector3f *vers, int offset,float cx, float cy, float r, int num_segments) {for(int i = 0; i < num_segments; i++) { //get the current angle float theta = 2.0f * PI * float(i) / float(num_segments);float x = r * cosf(theta);//calculate the x component float y = r * sinf(theta);//calculate the y component vers[offset+i] = Vector3f(x + cx, y + cy, 0.0f);//output vertex }}void createGeometry(){Vector3f vers[10];for (int i = 0, k = 0; i < 10; i+=2, k++){vers[i].x = (float)(penR * cos((18.0+72.0*k)*toPI));vers[i].y = (float)(penR * sin((18.0+72.0*k)*toPI));vers[i].z = 0.0f;vers[i+1].x = (float)(penInR * cos((72.0*k+54.0)*toPI));vers[i+1].y = (float)(penInR * sin((72.0*k+54.0)*toPI));vers[i+1].z = 0.0f;}Vector3f vers2[412] = {vers[0], vers[4], vers[5], vers[0], vers[5], vers[6],vers[2], vers[6], vers[7], vers[2], vers[7], vers[8]};DrawCircle(vers2, 12, 0.0f, 0.0f, (float)penR, 400);glGenBuffers(1, &VBO);glBindBuffer(GL_ARRAY_BUFFER, VBO);glBufferData(GL_ARRAY_BUFFER, sizeof(vers2), vers2, GL_STATIC_DRAW);}static void renderScene(){glClear(GL_COLOR_BUFFER_BIT);glEnableVertexAttribArray(0);glBindBuffer(GL_ARRAY_BUFFER, VBO);glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);glDrawArrays(GL_TRIANGLES, 0, 12);glDrawArrays(GL_LINE_LOOP, 12, 400);glDisableVertexAttribArray(0);glutSwapBuffers();}void initCallBack(){glutDisplayFunc(renderScene);}int run(int argc, char **argv){glutInit(&argc, argv);glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA);glutInitWindowSize(800, 600);glutInitWindowPosition(50, 50);glutCreateWindow("Bill's Another Pentagram");initCallBack();GLenum res = glewInit();if (res != GLEW_OK){fprintf(stderr, "Error: '%s'\n", glewGetErrorString(res));return 1;}createGeometry();glClearColor(0.0f, 0.6f, 0.2f, 0.0f);glutMainLoop();return 0;}}

OpenGL 3: Circle