Bresenham画椭圆算法.doc

这里不仔细讲原理，只是把我写的算法发出来，跟大家分享下，如果有错误的话，还请大家告诉我，如果写的不好，也请指出来，一起讨论进步。算法步骤:(1) 输入椭圆的长半轴a和短半轴b。(2) 计算初始值d = b*b + a * a * (-b + 0.25）， x = 0, y = b。(3) 绘制点 (x, y)及其在四分象限上的另外3个对称点。(4) 判断d的符号。若d = 0，则先将d更新为d + b * b * (2 * x + 3)，再将 (x, y)更新为(x+1, y)；否则先将d更新为d + b * b * (2 * x + 3) + a * a (-2 * y + 2)，再将(x, y)更新为(x+1, y-1)。(5) 当b*b * (x+1) a * a * (y - 0.5)时，重复步骤(3)和(4)，否则转到步骤(6)。(6) 用上半部分计算的最后点(x, y)来计算下半部分中d的初值: d = b * b * (x + 0.5) * (x + 0.5) + a * a * (y - 1) * (y - 1) - a * a * b * b。(7) 绘制点(x, y)及其在四分象限上的另外3个对称点。(8) 判断d的符号。若d = 0， 重复步骤(7)和(8)，否则结束。下面是算法:#include void init (void)glClearColor (0.0f, 0.0f, 0.0f, 1.0f);void drawEllipse (int a, int b, int xLoc, int yLoc)glPushMatrix ();int x, y;float d1, d2, aa, bb;aa = a * a;bb = b * b;d1 = bb + aa * (-b + 0.25);glTranslatef (GLfloat) xLoc, (GLfloat) yLoc, 0.0f);x = 0; y = b;glBegin (GL_POINTS);glVertex2i ( x, y);glVertex2i (-x, y);glVertex2i (-x, -y);glVertex2i ( x, -y);while (bb * (x + 1) aa * (y - 0.5)if (d1 = -0.000001)d1 += bb * (x 1) + 3);elsed1 += bb * (x 1) + 3) + aa * (2 - (y 1);- y;+ x;glVertex2i ( x, y);glVertex2i (-x, y);glVertex2i (-x, -y);glVertex2i ( x, -y);d2 = bb * (0.25 * x) + aa * (1 - (y 0)if (d2 = -0.000001)+ x;d2 += bb * (x + 1) 1) + aa * (3 - (y 1);elsed2 += aa * (3 - (y 1);- y;glVertex2i ( x, y);glVertex2i (-x, -y);glVertex2i (-x, y);glVertex2i ( x, -y);glEnd ();glPopMatrix ();void display (void)glClear (GL_COLOR_BUFFER_BIT);glLoadIdentity ();glColor3f (1.0f, 0.0f, 0.0f);/ draw a ellipsedrawEllipse (200, 300, 50, 50);glutSwapBuffers ();void reshape (int w, int h)glViewport (0, 0, (GLsizei) w, (GLsizei) h);glMatrixMode (GL_PROJECTION);glLoadIdentity ();if (w = h)gluOrtho2D (-600.0, 600.0, -600.0 * (GLfloat) h / (GLfloat) w, 600.0 * (GLfloat) h / (GLfloat) w);elsegluOrtho2D (-600.0 * (GLfloat) w / (GLfloat) h,600.0 * (GLfloat) w / (GLfloat) h, -600.0, 600.0);glMatrixMode (GL_MODELVIEW);glLoadIdentity ();void keyboard (unsigned char key, int x, int y)switch (key)case 27: / VK_ESCAPEexit (0);break;default:break;int main (int argc, char * argv)glutInit (&argc, argv);glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);glutInitWindowSize (600, 600);glutCreateWindow (Bresenham ellipse);init ();glutReshapeFunc (reshape);glutDisplayFunc (display);glutKeyboardFunc (keyboard);glutMainLoop ();return 0;努力不一定有结果，但不努力一定没结果。分类: 图形学(CG)绿色通道：好文要顶关注我收藏该文与我联系 风恋残