I am following this tutorial for arcball navigation in 3d:
https://en.wikibooks.org/wiki/OpenGL_Programming/Modern_OpenGL_Tutorial_Arcball
I managed to perform all the steps and the navigation works but I cant seem to comprehend last step in tutorial:
An extra trick is converting the rotation axis from camera coordinates to object coordinates. It's useful when the camera and object are placed differently. For instace, if you rotate the object by 90° on the Y axis ("turn its head" to the right), then perform a vertical move with your mouse, you make a rotation on the camera X axis, but it should become a rotation on the Z axis (plane barrel roll) for the object. By converting the axis in object coordinates, the rotation will respect that the user work in camera coordinates (WYSIWYG). To transform from camera to object coordinates, we take the inverse of the MV matrix (from the MVP matrix triplet).
The problem is that when i turn the model in the first step axis of rotation transform as well and they are not aligned with my "camera view". Of course I would like to keep my rotation axes always aligned with my camera view.
Can someone please give me an advice how to tackle it? In the tutorial there is a code but not much of explanation on what it is actually doing plus I only speak Python.
Thank you, Jacob
My code:
import pygame
from pygame.locals import *
from OpenGL.GL import *
from OpenGL.GLU import *
import math
import os
import numpy as np
size = 30
speed = 500
amplitude_amplificator = 80
color_table = ((1,0,0),
(0,1,0),
(0,0,1),
(1,1,0),
(1,0,1),
(0,1,1),
(1,0.5,0),
(0.5,1,0),
(0.5,1,0.5),
(0,0.5,0)
)
locations = ((0,-975, 0),
(0, 975, 0),
(-1273,-975, 0),
(-1273, 975, 0),
(-2482, -975, 0),
(-2482, 975, 0),
(-3737, -975, 0),
(-3737, 975, 0)
)
lines = ((0,2),
(2, 4),
(4, 6),
(1, 3),
(3, 5),
(5, 7),
(0, 1),
(2, 3),
(4, 5),
(6, 7),
)
amplitudes = ((3.38829249165602, 2.38305866657961, 2.52151563664636),
(5.08487438107113, 2.36432294667884, 3.0843991148654),
(3.44312569856563, 1.23112415468012, 1.29869765112226),
(4.0421066637935, 1.40655294535107, 1.36083778879317),
(3.78074337117764, 0.648255908566916, 0.752239154016233),
(5.08887133464996, 0.607037324785205, 0.543523234321567),
(4.49095206021647, 0.432732677308301, 2.18289872563964),
(5.14707697114171, 0.335119576625248, 2.15666871777855)
)
phases = ((-146.873017352057,0,-95.316526141321),
(-149.008372080797, 5.24886681104675, 78.3075732082314),
(-148.241584335287, 5.54327579087787, -118.279685417256),
(-151.844141596427, 6.48705235395368, -113.246406750217),
(-148.14233553496, 27.9523171503408, 65.8254568277543),
(-157.058723259828, 38.8760924034639, 85.2339573112435),
(-153.417593784393, -120.329988461629, 16.0421535833842),
(-156.779107376825, 83.2350395893582, 10.7592173681729)
)
# DRAW CUBE
def Cube(po,si,co):
POS = (
(po[0]+si, po[1]-si, po[2]-si),
(po[0]+si, po[1]+si, po[2]-si),
(po[0]-si, po[1]+si, po[2]-si),
(po[0]-si, po[1]-si, po[2]-si),
(po[0]+si, po[1]-si, po[2]+si),
(po[0]+si, po[1]+si, po[2]+si),
(po[0]-si, po[1]-si, po[2]+si),
(po[0]-si, po[1]+si, po[2]+si)
)
edges = (
(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)
for edge in edges:
for vertex in edge:
glColor3f(co[0],co[1],co[2])
glVertex3fv(POS[vertex])
glEnd()
#DRAW ORIGINAL SHAPE IN LINES
def Line_orig(po):
glBegin(GL_LINES)
for edge in po:
for vertex in edge:
glVertex3fv(locations[vertex])
glEnd()
#Hemisphere mapping
def map_hemisphere(x,y):
z = math.sqrt(abs(1-math.pow(x,2)-math.pow(y,2)))
return z
# Calculate angle of two spatial vectors
def angle_calculation(a,b):
r = math.degrees(math.acos((np.dot(a, b))/(np.linalg.norm(a)*np.linalg.norm(b))))
return r
def main():
mouse_pressed = 0
pygame.init()
display = (1200,800)
pygame.display.set_mode(display, DOUBLEBUF|OPENGL)
gluPerspective(45, (display[0]/display[1]), 0.1, 30000.0)
glTranslatef(0,0.0,-10000)
#glRotatef(90, 1, 0, 0)
while True:
for event in pygame.event.get():
if event.type == pygame.QUIT:
pygame.quit()
quit()
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT)
time = pygame.time.get_ticks()/1000
norm_mouse_pos = (2*pygame.mouse.get_pos()[0]/display[0]-1,2*pygame.mouse.get_pos()[1]/display[1]-1,map_hemisphere(2*pygame.mouse.get_pos()[0]/display[0]-1,2*pygame.mouse.get_pos()[1]/display[1]-1))
if pygame.mouse.get_pressed()[0]==1:
if mouse_pressed == 0:
mouse_pressed = 1
clear = lambda: os.system('cls')
clear()
p1 = (norm_mouse_pos[0],norm_mouse_pos[1],map_hemisphere(norm_mouse_pos[0],norm_mouse_pos[1]))
print(p1)
else:
p2 = (norm_mouse_pos[0],norm_mouse_pos[1],map_hemisphere(norm_mouse_pos[0],norm_mouse_pos[1]))
cist = np.cross(p1, p2)
print(angle_calculation(p1,p2))
glRotatef( angle_calculation(p1,p2) , -cist[0] , cist[1] , cist[2] )
else:
mouse_pressed = 0
# Translation of the model via keyboard handling
keys=pygame.key.get_pressed()
if keys[K_w]:
glTranslatef(0, 100, 0)
if keys[K_s]:
glTranslatef(0, -100, 0)
if keys[K_a]:
glTranslatef(-100, 0, 0)
if keys[K_d]:
glTranslatef(100, 0, 0)
# Drawing the Cubes at Nodes Loactions
for item, el in enumerate(locations):
Cube((el[0] + amplitudes[item][0]*math.sin(time + phases[item][0]*(3.1415927/180))*amplitude_amplificator,
el[1] + amplitudes[item][1]*math.sin(time + phases[item][1]*(3.1415927/180))*amplitude_amplificator,
el[2] + amplitudes[item][2]*math.sin(time + phases[item][2]*(3.1415927/180))*amplitude_amplificator
), size, color_table[item])
# Drawing the Original Shapes (Specified nodes in Lines Tuple)
Line_orig(lines)
# Drawing the Deformed Shape
glBegin(GL_LINES)
for edge in lines:
for vertex in edge:
glVertex3fv((locations[vertex][0] + amplitudes[vertex][0]*math.sin(time + phases[vertex][0]*(3.1415927/180))*amplitude_amplificator,
locations[vertex][1] + amplitudes[vertex][1]*math.sin(time + phases[vertex][1]*(3.1415927/180))*amplitude_amplificator ,
locations[vertex][2] + amplitudes[vertex][2]*math.sin(time + phases[vertex][2]*(3.1415927/180))*amplitude_amplificator,
))
glEnd()
# OpenGL Management
pygame.display.flip()
pygame.time.wait(10)
main()
