Question

当我运行此代码时，控制台将“无效值”显示为错误。我在书中进行了研究，但没有找到解决方法。他们甚至没有提到此值的含义。我想这将是存储在gluNewQuadric返回的指针中的地址号，该地址号可能超出GLUquadric类型的范围，但无法确定或修复它

#include <stdio.h>
#include <stdlib.h>
#include <GL/glut.h>

#ifndef CALLBACK
#define CALLBACK
#endif

void CALLBACK erro(GLenum coderro)
{
    const GLubyte *estring;
    estring=gluErrorString(coderro);
    fprintf(stderr, "Erro de quadrica: %s\n", estring);
    exit(0);
}


void tela ()
{
    GLUquadric *quadrica;
    glClearColor(1.0, 1.0, 1.0, 1.0);
    glClear(GL_COLOR_BUFFER_BIT);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(-30.0, 30.0, -30.0, 30.0, 1, 100);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glTranslated(0.0, 0.0, -20.0);

    glColor3f(1.0, 0.0, 0.0);
    quadrica=gluNewQuadric();
    gluQuadricCallback(quadrica, GLU_ERROR, erro);
    gluQuadricDrawStyle(quadrica, GLU_FILL);
    gluDisk(quadrica, 0.0, 5.0, 1, 1);

    glFlush();
}

int main (int argc, char **argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode( GLUT_SINGLE | GLUT_RGB );
    glutInitWindowSize(500, 500);
    glutCreateWindow("Tesselacao");
    glutDisplayFunc(tela);
    glutMainLoop();
}

Answer 1

请参阅gluDisk的规范：

 void gluDisk(    GLUquadric* quad,
     GLdouble inner,
     GLdouble outer,
     GLint slices,
     GLint loops);

参数
[...]
slices指定围绕z轴的细分数量。

这意味着slices必须至少为3，因为要生成形状，必须在磁盘周围至少有3个点。

例如

gluDisk(quadrica, 0.0, 5.0, 3, 1);将生成一个三角形，
gluDisk(quadrica, 0.0, 5.0, 5, 1);将生成一个五边形。

Answer 2

如果您在调试器中运行此命令并在erro处设置断点，则会发现以下内容（来自GDB的输出）：

Breakpoint 1, erro (coderro=100901) at test.c:12
12          estring=gluErrorString(coderro);
(gdb) bt
#0  erro (coderro=100901) at test.c:12
#1  0xf7dd7782 in gluQuadricError (qobj=0x81ddb70, which=100901) at src/libutil/quad.c:81
#2  0xf7dd85ad in gluPartialDisk (qobj=0x81ddb70, innerRadius=0, outerRadius=5, slices=1, loops=1, startAngle=0, sweepAngle=360) at src/libutil/quad.c:450
#3  0xf7dd84c8 in gluDisk (qobj=0x81ddb70, innerRadius=0, outerRadius=5, slices=1, loops=1) at src/libutil/quad.c:427
#4  0x08048af2 in tela () at test.c:36
#5  0xf7f72da8 in fghRedrawWindow () from /usr/lib/libglut.so.3
#6  0xf7f72df3 in fghcbDisplayWindow () from /usr/lib/libglut.so.3
#7  0xf7f77a90 in fgEnumWindows () from /usr/lib/libglut.so.3
#8  0xf7f72e47 in fghDisplayAll () from /usr/lib/libglut.so.3
#9  0xf7f73f39 in glutMainLoopEvent () from /usr/lib/libglut.so.3
#10 0xf7f73f97 in glutMainLoop () from /usr/lib/libglut.so.3
#11 0x08048b52 in main (argc=1, argv=0xffffd4e4) at test.c:48

因此，错误来自gluDisk。现在，简单尝试使用其参数，让我猜测罪魁祸首是slices=1，这确实没有道理。将其设置为2避免进入错误回调。

调用gluNewQuadric

2 个答案: