为什么在平移和更改摄影机角度时，我的有线球体会变成椭圆形?

问题描述

我需要沿z轴来回平移我的有线球体，同时还要更改摄影机角度.每当我的球体平移时，它就会慢慢变成椭圆体.我真的不明白为什么.在这里，您可以看到我认为是错误的代码段.同样，在调整窗口大小时，不应更改形状，而只能更改其大小.

I need to translate my wired sphere along z-axis back and forth while also changing camera angle. Whenever my sphere gets translated, it slowly turns into ellipsoid. I really don't understand why. Here you can see pieces of code where I believe is a mistake. Also, shapes shouldn't be changed when resizing the window, only their size.

void init() {
    glClearColor(0.0, 0.0, 0.0, 0.0);
      glEnable(GL_DEPTH_TEST);

    }


void display(void) {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

 glPushMatrix();
    glLoadIdentity();
    gluLookAt(ex, ey, ez, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
    glTranslatef(0.0,0.0,tra);
    glScalef(0.65, 0.65, 0.65);
    glColor3f(1.0f, 0.8f, 1.0f);
    glutWireSphere(0.65, 10, 15);
    glPopMatrix();

 glPushMatrix();
    glLoadIdentity();
    gluLookAt(ex, ey, ez, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
    glColor3f(0.1f, 0.8f, 1.0f);
    glutWireTorus(0.25, 1.0, 15, 15);
    glPopMatrix();
    glFlush();

    glFlush();
    }

void reshape(int w, int h) {
    glViewport(0, 0, (GLsizei)w, (GLsizei)h);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();


  gluPerspective(70.0, (GLfloat)w / (GLfloat)h, 1.0, 80.0);
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
    }

推荐答案

这是由透视畸变或广角畸变引起的，并向视图的边缘.可以通过减小视角范围来减小效果，但是效果永远不会被完全消除(平行投影除外).
参见als 如何修复透视投影变形?.

That's caused by the Perspective distortion or wide-angle distortion and increases towards the edge of the view. The effect can be decreased by reducing the field of view angle, but the effect will never be canceled completely (except parallel projection).
See als How to fix perspective projection distortion?.

在透视投影时，对象的大小始终是相对于视口的大小，而不是屏幕的大小.

At perspective projection the size of the objects is always relative to the size of the viewport rather than the size of your screen.

如果您不希望透视失真，并且想要对象的尺寸必须与屏幕尺寸(以像素为单位)相对，则必须使用相对于尺寸的正交投影视口.

If you don't want perspective distortion and if you want that the size of the objects has to be relative to the size of the screen (measured in pixel), then you have to use an orthographic projection, relative to the size of the viewport.

例如:

void reshape(int w, int h) {
    glViewport(0, 0, (GLsizei)w, (GLsizei)h);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    //gluPerspective(70.0, (GLfloat)w / (GLfloat)h, 1.0, 80.0);

    float sx = w / 100.0f;
    float sy = h / 100.0f;
    glOrtho(-sx/2.0f, sx/2.0f, -sy/2.0f, sy/2.0f, 1.0f, 80.0f);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

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