how to drag camera with the mouse like in blender

Question

i've found a program that you can move around the camera with the mouse in pyopengl, by doing some things i dont fully undesthand

from pygame.locals import *
import pygame
from OpenGL.GL import *
from OpenGL.GLU import *
from OpenGL.GLUT import *


def cube():
    vertices = (
        (1,-1,-1),
        (1,1,-1),
        (-1,1,-1),
        (-1,-1,-1),
        (1,-1,1),
        (1,1,1),
        (-1,-1,1),
        (-1,1,1)
    )
    edegs = (
        (0,1),
        (0,3),
        (0,4),
        (2,1),
        (2,3),
        (2,7),
        (6,3),
        (6,4),
        (6,7),
        (5,1),
        (5,4),
        (5,7),
    )
    glBegin(GL_LINES)
    glColor3fv((1,1,1))
    for edeg in edegs:
        for vertex in edeg:
            glVertex3fv(vertices[vertex])
    glEnd()
pygame.init()
screen = (800,600)
pygame.display.set_mode(screen, DOUBLEBUF|OPENGL)
glMatrixMode(GL_PROJECTION)

gluPerspective(45, (screen[0]/screen[1]), 0.1, 50.0)

glTranslate(0.0,0.0,-5)
glMatrixMode(GL_MODELVIEW)  
modelMatrix = glGetFloatv(GL_MODELVIEW_MATRIX)

busy = True
button_down = False
zoom = -0.5
while True:
    glPushMatrix()
    glLoadIdentity()

    for event in pygame.event.get():
        if(event.type == pygame.QUIT):
            pygame.quit()
            busy = False
        elif event.type == pygame.MOUSEMOTION:
            if(button_down):
                glRotatef(event.rel[1], 1, 0, 0)
                glRotatef(event.rel[0], 0, 1, 0)
        elif event.type == pygame.MOUSEBUTTONDOWN:
            if event.button == 4:
                zoom += 0.2
            if event.button == 5:
                zoom -= 0.2
    if(not busy): break
    for event in pygame.mouse.get_pressed():
        if pygame.mouse.get_pressed()[0] == 1:
            button_down = True
        elif pygame.mouse.get_pressed()[0] == 0:
            button_down = False
            
    #mouse scroll
    
            
    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT)
    glMultMatrixf(modelMatrix)
    modelMatrix = glGetFloatv(GL_MODELVIEW_MATRIX)

    glLoadIdentity()
    glTranslatef(0.0,0.0,zoom)
    
    glMultMatrixf(modelMatrix)

    cube()

    
    glPopMatrix()
    
        

    pygame.display.flip()
    pygame.time.wait(10)

But as you drag the object around it starts to lose the top to bottom orientation unlike programs like blender and sketchup, is there a way to fix that or another way to manipulate the camera?

Rabbid76 · Accepted Answer · 2021-12-17T21:18:49.877

Just sum up the rotation around the x-axis and the rotation around the y-axis. First rotate around the y-axis and than around the x-axis:

modelview = translate * rotateY * raotateX

Complete example:

from pygame.locals import *
import pygame
from OpenGL.GL import *
from OpenGL.GLU import *
from OpenGL.GLUT import *

def cube():
    vertices = (
        (1,-1,-1), (1,1,-1), (-1,1,-1), (-1,-1,-1),
        (1,-1,1), (1,1,1), (-1,-1,1), (-1,1,1)
    )
    edegs = (
        (0,1), (0,3), (0,4), (2,1), (2,3), (2,7),
        (6,3), (6,4), (6,7), (5,1), (5,4), (5,7),
    )
    glBegin(GL_LINES)
    glColor3fv((1,1,1))
    for edeg in edegs:
        for vertex in edeg:
            glVertex3fv(vertices[vertex])
    glColor3fv((1,0,0))    
    glVertex3f(0, -2, 0)  
    glVertex3f(0, 2, 0)    
    glEnd()

pygame.init()
screen = (400, 300)
pygame.display.set_mode(screen, DOUBLEBUF|OPENGL)

glEnable(GL_DEPTH_TEST)

glMatrixMode(GL_PROJECTION)
gluPerspective(45, (screen[0]/screen[1]), 0.1, 50.0)

glMatrixMode(GL_MODELVIEW)  
glTranslate(0.0,0.0,-5)

rot_x, rot_y, zoom = 0, 0, -0.5

clock = pygame.time.Clock()
busy = True
while busy:

    mouse_buttons = pygame.mouse.get_pressed()
    button_down = mouse_buttons[0] == 1
   
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            busy = False
        elif event.type == pygame.MOUSEMOTION:
            if button_down:
                rot_x += event.rel[1]
                rot_y += event.rel[0]
        elif event.type == pygame.MOUSEBUTTONDOWN:
            if event.button == 4:
                zoom += 0.2
            if event.button == 5:
                zoom -= 0.2
            
    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT)

    glPushMatrix()
    glTranslatef(0.0,0.0, zoom)
    glRotatef(rot_x, 1, 0, 0)    
    glRotatef(rot_y, 0, 1, 0)    
    cube()
    glPopMatrix()
    
    pygame.display.flip()
    clock.tick(100)

pygame.quit()

See also How to implement alt+MMB camera rotation like in 3ds max?, How to implement camera pan like in 3dsMax?, How to implement zoom towards mouse like in 3dsMax?.

how to drag camera with the mouse like in blender

1 Answers1