c++ - Bresenham 画圆算法的实现有什么问题？

Question

我已经实现了 Bresenham 圆算法。但这段代码只输出一个白色窗口。不绘制圆边界的单个像素。

该函数绘制 8 个对称点。

void plot_point(int x, int y, int xc, int yc)
{
    glBegin(GL_POINTS);
    glVertex2i(xc+x, yc+y);
    glVertex2i(xc+x, yc-y);
    glVertex2i(xc+y, yc+x);
    glVertex2i(xc+y, yc-x);
    glVertex2i(xc-x, yc-y);
    glVertex2i(xc-y, yc-x);
    glVertex2i(xc-x, yc+y);
    glVertex2i(xc-y, yc+x);
    glEnd();
}

该函数计算 x,y 坐标。

void bresenham_circle(int r)
{
    int x = 0, y = r, dx;

    plot_point(x, y, 0, 0);
    dx = 3 - 2*r;

    x += 1;
    if(dx >= 0)
        y -= 1;

    while(x < y)
    {
        plot_point(x, y, 0, 0);
        if(dx < 0)
            dx += 4*x + 6;
        else
            dx += 4*(x-y) + 10;

        if(dx >= 0)
            y -= 1;
        x += 1;
    }

    glFlush();
}

编辑:这是 main() 和 display() 函数:

void display()
{
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(1.0, 0.5, 0.0);

    int radius = 8;
    bresenham_circle(radius);
}

int main(int argc, char **argv)
{
    glutInit(&argc,argv);
    glutInitWindowPosition(0, 0);
    glutInitWindowSize(640,480);
    glutCreateWindow("Bresenham's Circle");
    glClearColor(1.0, 1.0, .5, 1.0);
    glutDisplayFunc(display);
    glutMainLoop();

    return 0;
}

我尝试绘制一些单点，即使在空间 [(-1, -1), (1, 1)] 中，但仍然什么也没有出现。

Answer 1

在我这边工作正常:

在放下圆形几何图形之前，请确保设置合理的投影/模型 View 矩阵+圆形半径(以及透明颜色/绘制颜色):

glClearColor( 0, 0, 0, 1 );
glClear(GL_COLOR_BUFFER_BIT);

glMatrixMode( GL_PROJECTION );
glLoadIdentity();
glOrtho( -100, 100, -100, 100, -1, 1 );

glMatrixMode( GL_MODELVIEW );
glLoadIdentity();

glColor3ub( 255, 255, 255 );
bresenham_circle( 50 );

一起:

#include <GL/glut.h>

void plot_point( int x, int y, int xc, int yc )
{
    glBegin( GL_POINTS );
    glVertex2i( xc + x, yc + y );
    glVertex2i( xc + x, yc - y );
    glVertex2i( xc + y, yc + x );
    glVertex2i( xc + y, yc - x );
    glVertex2i( xc - x, yc - y );
    glVertex2i( xc - y, yc - x );
    glVertex2i( xc - x, yc + y );
    glVertex2i( xc - y, yc + x );
    glEnd();
}

void bresenham_circle( int r )
{
    int x = 0, y = r, dx;

    plot_point( x, y, 0, 0 );
    dx = 3 - 2 * r;

    x += 1;
    if( dx >= 0 )
        y -= 1;

    while( x < y )
    {
        plot_point( x, y, 0, 0 );
        if( dx < 0 )
            dx += 4 * x + 6;
        else
            dx += 4 * ( x - y ) + 10;

        if( dx >= 0 )
            y -= 1;
        x += 1;
    }
}

void display()
{
    glClearColor( 0, 0, 0, 1 );
    glClear(GL_COLOR_BUFFER_BIT);

    glMatrixMode( GL_PROJECTION );
    glLoadIdentity();
    glOrtho( -100, 100, -100, 100, -1, 1 );

    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity();

    glColor3ub( 255, 255, 255 );
    bresenham_circle( 50 );

    glutSwapBuffers();
}

int main( int argc, char** argv )
{
    glutInit( &argc, argv );
    glutInitDisplayMode( GLUT_RGBA | GLUT_DOUBLE );
    glutCreateWindow( "GLUT" );
    glutDisplayFunc( display );
    glutMainLoop();
    return 0;
}