这次使用OpenGL画圆,而且中间画一个实心的五角星。
1. 画实心五角:
由于之前使用Polygen画会出现故障,或许是各个GPU硬件也会不一样的,所以使用Polygen画实心五角星并不可靠;
所以这里直接使用三角形画出五角星,不须要Polygen。
2 画圆
由于GLEW里面没有现成的圆形,所以仅仅能使用人工定顶点,然后画圆的方法;
当中的数学原理能够參考这里:http://slabode.exofire.net/circle_draw.shtml
最后得到效果:
非常美丽,非常标准的五角星外加一个圆形。
注:本程序仅仅使用Vertex Buffer,没使用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;
}
}