python - 如何使用 OpenGL 随时更改旋转半径

Question

我有一张 map ，我想围绕具有一定半径的点旋转。我设法做到了这一点，但我的问题是我有时想在旅途中改变半径并相应地更新相机

pygame.init()
display = (1700, 1000)
pygame.display.set_mode(display, DOUBLEBUF | OPENGL)
glMatrixMode(GL_PROJECTION)
glLoadIdentity()
gluPerspective(50, (display[0] / display[1]), 0.1, 5000)

glTranslatef(1, 1, -(radius/2))
glMatrixMode(GL_MODELVIEW)
glLoadIdentity()
glRotatef(10, 1, 0, 0) # i gave it 10 degrees for the camera to look at 
                       # the ground 
gluLookAt(offset_x - radius / 2, height, offset_z - radius / 2,
          offset_x, 0, offset_z,
          0, 1, 0)

# offset_x,offset_z are the center of the circle, 
# and the distance of rotation is the radius.
# This gets me to the point i want to be, everything is good so far. 

while True: 
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
    glPushMatrix()

    if not move: 
        glTranslatef(offset_x, 0, offset_z)
        glRotatef(rotation_angle, 0, 1, 0)
        glTranslatef(-offset_x, 0, -offset_z)
        rotation_angle += 0.5
    else:
        glTranslatef(offset_x, 0, offset_z)
        glRotatef(rotation_angle, 0, 1, 0)
        glTranslatef(-offset_x, 0, -offset_z)
    #### this rotates around the point at the start.
    #### the radius and the view distance is perfect. 

现在我从文本文件中获取新的半径，并且我想更改 View 以从新的半径距离围绕新的半径中心旋转。我有这个“if”知道半径何时改变，但我不明白如何使用 glTranslatef() 或 gluLookAt() 来更改围绕新点的旋转。

    #####################################################
    if radius_changed:
        glTranslatef(0, 0, radius - old_radius_copy) # this isnt working

        radius_changed = False
    else:
         glTranslatef(0, 0, radius - old_radius_copy) # this isnt working
    ######################################################


    glCallList(obj.gl_list)
    DrawBuffer(bufferObj, noPoints, noCirclePoints, noCrossPoints)
    glPopMatrix()

Answer 1

使用 glScalef() 将得到正确的结果，如下所示:

    if radius_changed:
        delta =  float(old_radius_copy) / float(radius)
        print delta
        scale_param_for_radius_change *= delta
        glTranslatef(offset_x, 0, offset_z)
        glScalef(scale_param_for_radius_change, 1, scale_param_for_radius_change)
        glTranslatef(-offset_x, 0, -offset_z)
        old_radius_copy = radius
        radius_changed = False
    else:
        glTranslatef(offset_x, 0, offset_z)
        glScalef(scale_param_for_radius_change, 1, scale_param_for_radius_change)
        glTranslatef(-offset_x, 0, -offset_z)