I am making a game in OpenGL which some objects goes toward you. To do that, I have to get the current camera location. I know that in OpenGL the camera always stay at (0,0,0) position, but I want to get the current location of the camera according to the world. How can I do that>
I've tried viewMatrix = glGetFloatv(GL_MODELVIEW_MATRIX)
camera_pos = viewMatrix[3], but my camera have pitch and yaw and the position always change when I am doing that. How can I solve this problem?
import pygame
from pygame.locals import *
from OpenGL.GL import *
from OpenGL.GLU import *
from OpenGL.GLUT import *
import math,random
while run:
for event in pygame.event.get():
if event.type == pygame.QUIT:
run = False
if event.type == pygame.KEYDOWN:
if event.key == pygame.K_ESCAPE:
run = False
if event.key == pygame.K_p:
paused = not paused
if not paused:
if event.type == pygame.MOUSEMOTION:
mouseMove = [event.pos[i] - displayCenter[i] for i in range(2)]
pygame.mouse.set_pos(displayCenter)
pygame.mouse.set_visible(False)
if not paused:
#Get keys
keypress = pygame.key.get_pressed()
#Init model view matrix
glLoadIdentity()
#------------------------View------------------------
#Apply the look up and down (with 90° angle limit)
if up_down_angle < -90:
if mouseMove[1] > 0:
up_down_angle += mouseMove[1]*0.1
elif up_down_angle > 90:
if mouseMove[1] < 0:
up_down_angle += mouseMove[1]*0.1
else:
up_down_angle += mouseMove[1]*0.1
glRotatef(up_down_angle, 1.0, 0.0, 0.0)
#Init the view matrix
glPushMatrix()
glLoadIdentity()
#Apply the movement
if keypress[pygame.K_w]:
glTranslatef(0,0,0.1)
if keypress[pygame.K_s]:
glTranslatef(0,0,-0.1)
if keypress[pygame.K_d]:
glTranslatef(-0.1,0,0)
if keypress[pygame.K_a]:
glTranslatef(0.1,0,0)
#Apply the look left and right
glRotatef(mouseMove[0]*0.1, 0.0, 1.0, 0.0)
#------------------------View------------------------
#------------------------Draw------------------------
#Multiply the current matrix by the new view matrix and store the final view matrix
glMultMatrixf(viewMatrix)
viewMatrix = glGetFloatv(GL_MODELVIEW_MATRIX)
camera_pos = viewMatrix[3] #Incorrect
print(camera_pos) #print the output
#Apply view matrix
glPopMatrix()
glMultMatrixf(viewMatrix)
glLightfv(GL_LIGHT0, GL_POSITION, [1, -1, 1, 0])
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT)
glPushMatrix()
glColor4f(0.2, 0.2, 0.5, 1)
for person in persons:
person.draw()
ground.draw()
glutSwapBuffers()
glPopMatrix()
#------------------------Draw------------------------
pygame.display.flip()
pygame.time.wait(10)
pygame.quit()
I expect when I do the view rotation my coordinates won't move, but the output of camera_pos changes when doing that.
The view matrix transforms form world space to view space. This means the view matrix is not the matrix which contains the camera position. The view matrix is the inverse matrix which contains the camera position and orientation.
Write a function which can can calculate the inverse matrix of a 4x4 matrix:
def InverseMat44(mat):
m = [mat[i][j] for i in range(4) for j in range(4)]
inv = [0]*16
inv[0] = m[5] * m[10] * m[15] - m[5] * m[11] * m[14] - m[9] * m[6] * m[15] + m[9] * m[7] * m[14] + m[13] * m[6] * m[11] - m[13] * m[7] * m[10]
inv[4] = -m[4] * m[10] * m[15] + m[4] * m[11] * m[14] + m[8] * m[6] * m[15] - m[8] * m[7] * m[14] - m[12] * m[6] * m[11] + m[12] * m[7] * m[10]
inv[8] = m[4] * m[9] * m[15] - m[4] * m[11] * m[13] - m[8] * m[5] * m[15] + m[8] * m[7] * m[13] + m[12] * m[5] * m[11] - m[12] * m[7] * m[9]
inv[12] = -m[4] * m[9] * m[14] + m[4] * m[10] * m[13] + m[8] * m[5] * m[14] - m[8] * m[6] * m[13] - m[12] * m[5] * m[10] + m[12] * m[6] * m[9]
inv[1] = -m[1] * m[10] * m[15] + m[1] * m[11] * m[14] + m[9] * m[2] * m[15] - m[9] * m[3] * m[14] - m[13] * m[2] * m[11] + m[13] * m[3] * m[10]
inv[5] = m[0] * m[10] * m[15] - m[0] * m[11] * m[14] - m[8] * m[2] * m[15] + m[8] * m[3] * m[14] + m[12] * m[2] * m[11] - m[12] * m[3] * m[10]
inv[9] = -m[0] * m[9] * m[15] + m[0] * m[11] * m[13] + m[8] * m[1] * m[15] - m[8] * m[3] * m[13] - m[12] * m[1] * m[11] + m[12] * m[3] * m[9]
inv[13] = m[0] * m[9] * m[14] - m[0] * m[10] * m[13] - m[8] * m[1] * m[14] + m[8] * m[2] * m[13] + m[12] * m[1] * m[10] - m[12] * m[2] * m[9]
inv[2] = m[1] * m[6] * m[15] - m[1] * m[7] * m[14] - m[5] * m[2] * m[15] + m[5] * m[3] * m[14] + m[13] * m[2] * m[7] - m[13] * m[3] * m[6]
inv[6] = -m[0] * m[6] * m[15] + m[0] * m[7] * m[14] + m[4] * m[2] * m[15] - m[4] * m[3] * m[14] - m[12] * m[2] * m[7] + m[12] * m[3] * m[6]
inv[10] = m[0] * m[5] * m[15] - m[0] * m[7] * m[13] - m[4] * m[1] * m[15] + m[4] * m[3] * m[13] + m[12] * m[1] * m[7] - m[12] * m[3] * m[5]
inv[14] = -m[0] * m[5] * m[14] + m[0] * m[6] * m[13] + m[4] * m[1] * m[14] - m[4] * m[2] * m[13] - m[12] * m[1] * m[6] + m[12] * m[2] * m[5]
inv[3] = -m[1] * m[6] * m[11] + m[1] * m[7] * m[10] + m[5] * m[2] * m[11] - m[5] * m[3] * m[10] - m[9] * m[2] * m[7] + m[9] * m[3] * m[6]
inv[7] = m[0] * m[6] * m[11] - m[0] * m[7] * m[10] - m[4] * m[2] * m[11] + m[4] * m[3] * m[10] + m[8] * m[2] * m[7] - m[8] * m[3] * m[6]
inv[11] = -m[0] * m[5] * m[11] + m[0] * m[7] * m[9] + m[4] * m[1] * m[11] - m[4] * m[3] * m[9] - m[8] * m[1] * m[7] + m[8] * m[3] * m[5]
inv[15] = m[0] * m[5] * m[10] - m[0] * m[6] * m[9] - m[4] * m[1] * m[10] + m[4] * m[2] * m[9] + m[8] * m[1] * m[6] - m[8] * m[2] * m[5]
det = m[0] * inv[0] + m[1] * inv[4] + m[2] * inv[8] + m[3] * inv[12]
for i in range(16):
inv[i] /= det;
return inv;
See also inverting a 4x4 matrix and Find the inverse of a 4×4 matrix.
And calculate the inverse matrix of the view matrix:
viewMatrix = glGetFloatv(GL_MODELVIEW_MATRIX)
invVM = InverseMat44(viewMatrix)
camera_pos = (invVM[12], invVM[13], invVM[14])
print(camera_pos)
The inverse matrix can also be calculated by libraries. e.g. numpy.linalg.inv from NumPy library or glm.inverse from PyGLM library.