円を描画する - OpenGLプログラミングメモ

円を描画します。
OpenGLには円を描く機能はありませんので関数を自作します。
楕円も描画できるようにしておきました。
ここから再描画用にIdleコールバック関数とチラつき防止のために
ダブルバッファリングが登場します。

 

ファイル

main.cpp

main.cpp

#pragma comment(linker, "/SUBSYSTEM:WINDOWS /ENTRY:mainCRTStartup") #include <GL/freeglut/freeglut.h> #include <math.h> #define WIDTH 320 #define HEIGHT 240 #define Pai 3.1415926 void Circle2D(float radius,int x,int y) {  for (float th1 = 0.0;  th1 <= 360.0;  th1 = th1 + 1.0)  {                float th2 = th1 + 10.0;   float th1_rad = th1 / 180.0 * Pai;    float th2_rad = th2 / 180.0 * Pai;   float x1 = radius * cos(th1_rad);   float y1 = radius * sin(th1_rad);   float x2 = radius * cos(th2_rad);   float y2 = radius * sin(th2_rad);   glBegin(GL_LINES);       glVertex2f( x1+x, y1+y );         glVertex2f( x2+x, y2+y );   glEnd();  } } void Circle2DFill(float radius,int x,int y) {  for (float th1 = 0.0;  th1 <= 360.0;  th1 = th1 + 1.0)  {                float th2 = th1 + 10.0;   float th1_rad = th1 / 180.0 * Pai;    float th2_rad = th2 / 180.0 * Pai;   float x1 = radius * cos(th1_rad);   float y1 = radius * sin(th1_rad);   float x2 = radius * cos(th2_rad);   float y2 = radius * sin(th2_rad);   glBegin(GL_TRIANGLES);     glVertex2f( x, y );    glVertex2f( x1+x, y1+y );         glVertex2f( x2+x, y2+y );   glEnd();  }  } void Oval2D(float radius,int x,int y,float ovalx,float ovaly) {  for (float th1 = 0.0;  th1 <= 360.0;  th1 = th1 + 1.0)  {                float th2 = th1 + 10.0;   float th1_rad = th1 / 180.0 * Pai;    float th2_rad = th2 / 180.0 * Pai;   float x1 = radius * cos(th1_rad)*(ovalx/100.0f);   float y1 = radius * sin(th1_rad)*(ovaly/100.0f);   float x2 = radius * cos(th2_rad)*(ovalx/100.0f);   float y2 = radius * sin(th2_rad)*(ovaly/100.0f);   glBegin(GL_LINES);       glVertex2f( x1+x, y1+y );         glVertex2f( x2+x, y2+y );   glEnd();  } } void Oval2DFill(float radius,int x,int y,float ovalx,float ovaly) {  for (float th1 = 0.0;  th1 <= 360.0;  th1 = th1 + 1.0)  {                float th2 = th1 + 10.0;   float th1_rad = th1 / 180.0 * Pai;    float th2_rad = th2 / 180.0 * Pai;   float x1 = radius * cos(th1_rad)*(ovalx/100.0f);   float y1 = radius * sin(th1_rad)*(ovaly/100.0f);   float x2 = radius * cos(th2_rad)*(ovalx/100.0f);   float y2 = radius * sin(th2_rad)*(ovaly/100.0f);   glBegin(GL_TRIANGLES);     glVertex2f( x, y );    glVertex2f( x1+x, y1+y );         glVertex2f( x2+x, y2+y );   glEnd();  } } void display(void) {  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);  glColor4f(1.0f, 0.0f, 0.0f, 1.0f);  Circle2D(40.0f,50,50);  glColor4f(0.0f, 0.0f, 1.0f, 1.0f);  Circle2DFill(50.0f,150,180);  glColor4f(0.0f, 1.0f, 0.0f, 1.0f);  Oval2D(50.0f,150,80,100.0f,80.0f);  glColor4f(0.0f, 0.0f, 0.0f, 1.0f);  Oval2DFill(80.0f,260,120,50.0f,100.0f);  glutSwapBuffers(); } void idle(void) {  glutPostRedisplay(); } void Init(){  glClearColor(1.0, 1.0, 1.0, 1.0);  glOrtho(0, WIDTH, HEIGHT, 0, -1, 1); } int main(int argc, char *argv[]) {  glutInitWindowPosition(100, 100);  glutInitWindowSize(WIDTH, HEIGHT);  glutInit(&argc, argv);  glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE);  glutCreateWindow("円を描画");  glutDisplayFunc(display);  glutIdleFunc(idle);  Init();  glutMainLoop();  return 0; }