OpenGL 洪水填充无法识别边界

OpenGL flood fill not recognizing boundary

我正在尝试在 OpenGL 中实现洪水填充算法,但我遇到了一个错误。错误是算法并没有在边界处停止,而是一直持续到 window 的边缘,最终因错误的内存访问错误而崩溃。我正在使用 MacOS Mojave 10.14.4。

我认为我的实现逻辑是正确的,但是,我已经从 getPixel 中打印出每个像素的颜色,并且它始终是白色(背景颜色),即使在获取边界颜色时也是如此像素.

下面的代码使用Bresenham's Line algorithm(中点算法)画了一个圆,然后flood fill了它(未成功)。

#include <GLUT/GLUT.h>
#include <iostream>


struct Color {
    GLubyte r;
    GLubyte g;
    GLubyte b;
};

Color getPixelColor(GLint x, GLint y) {
    Color color;
    glReadPixels(x, y, 1, 1, GL_RGB, GL_UNSIGNED_BYTE, &color);
    return color;
}

void setPixel (GLint x, GLint y) {
    glBegin(GL_POINTS);
    glVertex2i(x, y);
    glEnd();
    Color color = getPixelColor(x, y);
}


void setPixelColor(GLint x, GLint y, Color color) {
    glColor3ub(color.r, color.g, color.b);
    setPixel(x, y);
    glEnd();
    glFlush();
}

void floodFill4 (GLint x, GLint y, Color fillColor, Color interiorColor) {
    Color color = getPixelColor(x, y);
    if (color.r == interiorColor.r && color.g == interiorColor.g &&
        color.b == interiorColor.b) {
        setPixelColor(x, y, fillColor);
        floodFill4 (x + 1, y, fillColor, interiorColor);
        floodFill4 (x - 1, y, fillColor, interiorColor);
        floodFill4 (x, y + 1, fillColor, interiorColor);
        floodFill4 (x, y - 1, fillColor, interiorColor);
    }
}

void drawCirclePoint(GLint x, GLint y, GLint cx, GLint cy) {
    setPixel(cx+x, cy+y);
    setPixel(cx+y, cy+x);
    setPixel(cx-y, cy+x);
    setPixel(cx-x, cy+y);
    setPixel(cx-x, cy-y);
    setPixel(cx-y, cy-x);
    setPixel(cx+y, cy-x);
    setPixel(cx+x, cy-y);
}

void drawCircle(GLint cx, GLint cy, GLint radius) {
    int p = 1 - radius;
    GLint x = 0;
    GLint y = radius;
    while (x < y) {
        drawCirclePoint(x, y, cx, cy);
        if (p < 0) {
            x++;
            p += (2 * x) + 1;
        } else {
            x++;
            y--;
            p += (2 * x) + 1 - (2 * y);
        }
    }
}


void displayMe(void) {
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3ub(0, 0, 0);
    GLint cx = 0;
    GLint cy = 0;
    GLint radius = 200;
    // Draw head
    glColor3ub(0, 0, 0);
    drawCircle(cx, cy, radius);
    glEnd();
    glFlush();
    Color interiorColor = {255, 255, 255};
    Color fillColor = {0, 0, 255};
//    floodFill4(100, 100, fillColor, interiorColor);
}

void init (void) {
    glClearColor(1.0, 1.0, 1.0, 0.0);  // Set display-window color to white.
    glMatrixMode(GL_PROJECTION);       // Set projection parameters.
    glLoadIdentity();
    gluOrtho2D(-1000.0, 1000.0, -1000.0, 1000.0);
    glMatrixMode(GL_MODELVIEW);
}

int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(1000, 1000);
    glutInitWindowPosition(100, 100);
    glutCreateWindow("My Drawing");
    init();
    glutDisplayFunc(displayMe);
    glutMainLoop();
    return 0;
}

我看过 ,看起来很相似,但找不到解决方案。

如果您要坚持使用 glVertex() 进行点绘图,请确保设置矩阵堆栈变换 (GL_PROJECTION/GL_MODELVIEW),以便它们与 glReadPixels()坐标系:

glMatrixMode( GL_PROJECTION );
glLoadIdentity();
gluOrtho2D( 0, glutGet(GLUT_WINDOW_WIDTH), 0, glutGet(GLUT_WINDOW_HEIGHT) );
glMatrixMode( GL_MODELVIEW );
glLoadIdentity();

或切换到 glRasterPos() + glDrawPixels() for setPixel*().

更好的是,执行 flood-fill 逻辑 host-side 并将结果上传到 GL 纹理以供显示。

无论哪种方式,你都会 运行 使用递归解决方案在相当合理大小的输入上进入堆栈溢出,所以你可能想要切换到显式堆栈/queue

void floodFill4( GLint aX, GLint aY, Color fillColor, Color interiorColor )
{
    typedef std::pair< GLint, GLint > Location;
    std::queue< Location > locations;

    locations.push( Location( aX, aY ) );
    while( !locations.empty() )
    {
        const Location loc = locations.front();
        locations.pop();

        GLint x = loc.first;
        GLint y = loc.second;

        Color color = getPixelColor( x, y );
        if( color.r == interiorColor.r &&
            color.g == interiorColor.g &&
            color.b == interiorColor.b )
        {
            setPixelColor( x, y, fillColor );
            locations.push( Location( x, y - 1 ) );
            locations.push( Location( x, y + 1 ) );
            locations.push( Location( x - 1, y ) );
            locations.push( Location( x + 1, y ) );
        }
    }
}