Is it possible to create physics simulation (with Bullet Physics Engine) without the `render` object

Scripting Issues
1

Hi,

Is it possible to create physics simulation without the render object?

I tried but it prints the identity matrices:

from panda3d.bullet import BulletWorld
from panda3d.core import Vec3
from panda3d.bullet import BulletBoxShape
from panda3d.bullet import BulletRigidBodyNode

world = BulletWorld()
world.setGravity(Vec3(0, 0, -9.81))

shape = BulletBoxShape(Vec3(0.5, 0.5, 0.5))
node = BulletRigidBodyNode('Box')
node.setMass(1.0)
node.addShape(shape)
world.attachRigidBody(node)

for i in range(10):
    world.doPhysics(0.016)
    print(node.getShapeTransform(0))
1 Like
2

Try printing node.getTransform() instead. getShapeTransform() returns the relative transform of the physics shape to the node it is applied to. The physics simulation is applied to the node.

1 Like
3

Yes, you are right. Thank you!

It returns positions:

T:(identity)
T:(pos 0 0 -0.002507)
T:(pos 0 0 -0.007521)
T:(pos 0 0 -0.015042)
T:(pos 0 0 -0.02507)
T:(pos 0 0 -0.037605)
T:(pos 0 0 -0.052647)
T:(pos 0 0 -0.070196)
T:(pos 0 0 -0.090252)
T:(pos 0 0 -0.112815)

But how to return angles?

4

I need something like getQuaternion()

5

I tried to add a quaternion to TransformState but I do not see quat in the output:

T:(pos 0 0 -0.02507)

main.py

from panda3d.core import TransformState, Vec3, Quat, Point3
from panda3d.bullet import BulletWorld
from panda3d.bullet import BulletBoxShape
from panda3d.bullet import BulletRigidBodyNode

world = BulletWorld()
world.setGravity(Vec3(0, 0, -9.81))
shape = BulletBoxShape(Vec3(0.5, 0.5, 0.5))
node = BulletRigidBodyNode('Box')
node.setMass(1.0)

p = Point3(0, 0, 0)
q = Quat.identQuat()
s = Vec3(1, 1, 1)

transform = TransformState.make_pos_quat_scale(p, q, s)
node.setTransform(transform)
node.addShape(shape)
world.attachRigidBody(node)

for i in range(10):
    world.doPhysics(0.016)
    print(node.getTransform())
6

I understand now. quat will be here when it will be changed. It does not show default values. I just added another scale and now I see scale in the output:

p = Point3(1, 0, 0)
q = Quat.identQuat()
s = Vec3(2, 2, 2)

Output:

T:(pos 1 0 0 scale 2)
T:(pos 1 0 -0.002507 scale 2)
T:(pos 1 0 -0.007521 scale 2)
T:(pos 1 0 -0.015042 scale 2)
T:(pos 1 0 -0.02507 scale 2)
T:(pos 1 0 -0.037605 scale 2)
...
7

This example helped me: Memory Leak in Bullet Code - #5 by enn0x

rom panda3d.core import Vec3
from panda3d.core import Point3
from panda3d.core import Quat
from panda3d.core import TransformState

q = Quat.identQuat()
s = Vec3(1,1,1)

i = 0
while True:
   i += 1
   p = Point3(0,0,i*0.001)
   ts = TransformState.makePosQuatScale(p,q,s)
8

Thank you very much for the Panda3D Bullet wrapper. I tried to use PyBullet but it is very complicated and I cannot understand haw to use it with OpenGL. The Panda3D Bullet wrapper is only one way that I found. And there is a very great manual: Using Bullet with Panda3D — Panda3D Manual I hope I will not have unresolved problems with using the Panda3D Bullet wrapper with Qt and OpenGL.

I wrote an interesting example. I use:

  • the Panda3D Bullet wrapper for Physics
  • PyQt5 (and PySide2) for creating a window
  • OpenGL 3.3 for rendering

I created a textured cube with Blender and GIMP. I exported the cube to dae (COLLADA) and imported it to my program with built-in Qt XML parser.

Source:

textured_cubes_bullet_pyqt5

PyQt5:

import sys
import numpy as np
from OpenGL import GL as gl
from PyQt5.QtWidgets import QApplication, QOpenGLWidget
from PyQt5.QtGui import QOpenGLShaderProgram, QOpenGLShader, QOpenGLBuffer
from PyQt5.QtGui import QOpenGLTexture, QImage
from PyQt5.QtGui import QMatrix4x4, QVector3D, QQuaternion
from PyQt5.QtXml import QDomDocument, QDomElement
from PyQt5.QtCore import Qt, QFile, QIODevice
from PyQt5.QtCore import QTimer, QElapsedTimer

from panda3d.bullet import BulletWorld
from panda3d.core import TransformState, Vec3, Quat, Point3
from panda3d.bullet import BulletBoxShape
from panda3d.bullet import BulletRigidBodyNode

# Assets:
# Cube Texture: https://dl.dropboxusercontent.com/s/tply9ubx3n3ycvv/cube.png
# Cube Model: https://dl.dropboxusercontent.com/s/0aktc37c3nx9iq3/cube.dae
# Plane Texture: https://dl.dropboxusercontent.com/s/3iibsnvyw0vupby/plane.png
# Plane Model: https://dl.dropboxusercontent.com/s/e0wktg69ec3w8pq/plane.dae

class VertexBuffers:
    vertex_pos_buffer = None
    normal_buffer = None
    tex_coord_buffer = None
    amount_of_vertices = None

class Locations:
    mvp_matrix_location = None
    model_matrix_location = None
    normal_matrix_location = None

class Object3D:
    position = QVector3D(0, 0, 0)
    rotation = QVector3D(0, 0, 0)
    scale = QVector3D(1, 1, 1)
    mvp_matrix = QMatrix4x4()
    model_matrix = QMatrix4x4()
    normal_matrix = QMatrix4x4()

    def __init__(self, vert_buffers, locations, texture, world, mass, pos):
        self.vert_pos_buffer = vert_buffers.vert_pos_buffer
        self.normal_buffer = vert_buffers.normal_buffer
        self.tex_coord_buffer = vert_buffers.tex_coord_buffer
        self.amount_of_vertices = vert_buffers.amount_of_vertices
        
        self.mvp_matrix_location = locations.mvp_matrix_location
        self.model_matrix_location = locations.model_matrix_location
        self.normal_matrix_location = locations.normal_matrix_location
        
        self.texture = texture

        self.shape = BulletBoxShape(Vec3(0.5, 0.5, 0.5))
        self.node = BulletRigidBodyNode('Box')

        self.position = pos
        self.mass = mass
        self.node.setMass(self.mass)

        p = Point3(self.position.x(), self.position.y(), self.position.z())
        q = Quat.identQuat()
        s = Vec3(1, 1, 1)

        self.transform = TransformState.make_pos_quat_scale(p, q, s)
        self.node.setTransform(self.transform)

        self.node.addShape(self.shape)
        self.world = world
        self.world.attachRigidBody(self.node)

    def draw(self, program, proj_view_matrix):
        program.bind()

        self.vert_pos_buffer.bind()
        program.setAttributeBuffer(0, gl.GL_FLOAT, 0, 3)
        program.enableAttributeArray(0)

        self.normal_buffer.bind()
        program.setAttributeBuffer(1, gl.GL_FLOAT, 0, 3)
        program.enableAttributeArray(1)

        self.tex_coord_buffer.bind()
        program.setAttributeBuffer(2, gl.GL_FLOAT, 0, 2)
        program.enableAttributeArray(2)

        self.position.setX(self.node.getTransform().pos.x)
        self.position.setY(self.node.getTransform().pos.y)
        self.position.setZ(self.node.getTransform().pos.z)
        hpr = self.node.getTransform().getHpr()
        pandaQuat = Quat()
        pandaQuat.setHpr(hpr)
        quat = QQuaternion(pandaQuat.getX(), pandaQuat.getY(), pandaQuat.getZ(), pandaQuat.getW())
        
        self.model_matrix.setToIdentity()
        self.model_matrix.translate(self.position)
        self.model_matrix.rotate(quat)
        self.model_matrix.scale(self.scale)
        self.mvp_matrix = proj_view_matrix * self.model_matrix
        
        self.normal_matrix = self.model_matrix.inverted()
        self.normal_matrix = self.normal_matrix[0].transposed()
        
        program.bind()
        program.setUniformValue(self.mvp_matrix_location, self.mvp_matrix)
        program.setUniformValue(self.model_matrix_location, self.model_matrix)
        program.setUniformValue(self.normal_matrix_location, self.normal_matrix)
        
        self.texture.bind()

        gl.glDrawArrays(gl.GL_TRIANGLES, 0, self.amount_of_vertices)

class Window(QOpenGLWidget):

    def __init__(self):
        super().__init__()
        self.setWindowTitle("Bullet Physics")
        self.resize(268, 268)

    def initializeGL(self):
        gl.glClearColor(0.2, 0.2, 0.2, 1)
        gl.glEnable(gl.GL_DEPTH_TEST)
        vertShaderSrc = """
            #version 330 core

            in vec4 aPosition;
            in vec4 aNormal;
            in vec2 aTexCoord;

            uniform mat4 uMvpMatrix;
            uniform mat4 uModelMatrix;
            uniform mat4 uNormalMatrix;

            out vec3 vPosition;
            out vec3 vNormal;
            out vec2 vTexCoord;

            void main()
            {
                gl_Position = uMvpMatrix * aPosition;
                vPosition = vec3(uModelMatrix * aPosition);
                vNormal = normalize(vec3(uNormalMatrix * aNormal));
                vTexCoord = aTexCoord;
            }
        """
        fragShaderSrc = """
            #version 330 core

            const vec3 lightColor = vec3(0.8, 0.8, 0.8);
            const vec3 lightPosition = vec3(5.0, 7.0, 2.0);
            const vec3 ambientLight = vec3(0.3, 0.3, 0.3);

            uniform sampler2D uSampler;

            in vec3 vPosition;
            in vec3 vNormal;
            in vec2 vTexCoord;

            void main()
            {
                vec4 color = texture2D(uSampler, vTexCoord);
                vec3 normal = normalize(vNormal);
                vec3 lightDirection = normalize(lightPosition - vPosition);
                float nDotL = max(dot(lightDirection, normal), 0.0);
                vec3 diffuse = lightColor * color.rgb * nDotL;
                vec3 ambient = ambientLight * color.rgb;
                gl_FragColor = vec4(diffuse + ambient, color.a);
            }
        """
        self.program = QOpenGLShaderProgram()
        self.program.addShaderFromSourceCode(QOpenGLShader.Vertex, vertShaderSrc)
        self.program.addShaderFromSourceCode(QOpenGLShader.Fragment, fragShaderSrc)
        self.program.link()
        self.program.bind()
        self.program.bindAttributeLocation("aPosition", 0)
        self.program.bindAttributeLocation("aNormal", 1)
        self.program.bindAttributeLocation("aTexCoord", 2)
        locations = Locations()
        self.program.bind()
        locations.mvp_matrix_location = self.program.uniformLocation("uMvpMatrix")
        locations.model_matrix_location = self.program.uniformLocation("uModelMatrix")
        locations.normal_matrix_location = self.program.uniformLocation("uNormalMatrix")
        self.vert_buffers = self.initVertexBuffers("assets/cube.dae")
        self.proj_view_matrix = QMatrix4x4()
        self.proj_matrix = QMatrix4x4()
        self.view_matrix = QMatrix4x4()
        self.view_matrix.lookAt(
            QVector3D(2, 3, 5),
            QVector3D(0, 0, 0),
            QVector3D(0, 1, 0))
        
        self.texture = QOpenGLTexture(QOpenGLTexture.Target2D)
        self.texture.create()
        self.texture.setData(QImage("assets/cube.png"))
        self.texture.setMinMagFilters(QOpenGLTexture.Linear, QOpenGLTexture.Linear)
        self.texture.setWrapMode(QOpenGLTexture.ClampToEdge)

        self.world = BulletWorld()
        self.world.setGravity(Vec3(0, -9.81, 0))

        self.obj = Object3D(self.vert_buffers, locations, self.texture, self.world, mass=0, pos=QVector3D(0, -3, 0))
        self.obj2 = Object3D(self.vert_buffers, locations, self.texture, self.world, mass=1, pos=QVector3D(0.8, 3, 0))
        
        #self.move_dir = 1 # move direction: 1 - up, -1 - down
        #self.move_speed = 0.002
        
        self.timer = QTimer()
        self.timer.timeout.connect(self.animationLoop)
        self.elapsed_timer = QElapsedTimer()
        self.elapsed_timer.start()
        self.delta_time = 0
        self.timer.start(1000/60)
        
    def animationLoop(self):
        self.delta_time = self.elapsed_timer.elapsed()
        self.elapsed_timer.restart()
        self.world.doPhysics(self.delta_time / 1000)
        self.update()
        
    def paintGL(self):
        gl.glClear(gl.GL_COLOR_BUFFER_BIT | gl.GL_DEPTH_BUFFER_BIT)
        self.proj_view_matrix = self.proj_matrix * self.view_matrix
        self.obj.draw(self.program, self.proj_view_matrix)
        self.obj2.draw(self.program, self.proj_view_matrix)

    def resizeGL(self, w, h):
        gl.glViewport(0, 0, w, h)
        self.proj_matrix.setToIdentity()
        self.proj_matrix.perspective(50, float(w) / float(h), 0.1, 100)
        
    def initVertexBuffers(self, path):
        xml_doc = QDomDocument()
        file = QFile(path)
        if not file.open(QIODevice.ReadOnly):
            print("Failed to open the file: " + path)
        xml_doc.setContent(file)
        file.close()
        
        vert_pos_array = []
        normal_array = []
        tex_coord_array = []
        index_array = []
        
        root = xml_doc.documentElement()
        dae_elem = root.firstChildElement()
        while not dae_elem.isNull():
            if dae_elem.tagName() == "library_geometries":
                geom_elem = dae_elem.firstChildElement()
                if geom_elem.tagName() == "geometry":
                    mesh_elem = geom_elem.firstChildElement()
                    if mesh_elem.tagName() == "mesh":
                        mesh_child_elem = mesh_elem.firstChildElement()
                        while not mesh_child_elem.isNull():
                            float_array_elem = mesh_child_elem.firstChildElement()
                            str_array = float_array_elem.firstChild().toText().data().split(" ")
                            if mesh_child_elem.attribute("id").endswith("-mesh-positions"):
                                vert_pos_array = list(map(float, str_array))
                            if mesh_child_elem.attribute("id").endswith("-mesh-normals"):
                                normal_array = list(map(float, str_array))
                            if mesh_child_elem.attribute("id").endswith("-mesh-map-0"):
                                tex_coord_array = list(map(float, str_array))
                            if mesh_child_elem.tagName() == "triangles" or mesh_child_elem.tagName() == "polylist":
                                p_child_elem = mesh_child_elem.firstChildElement()
                                while not p_child_elem.isNull():
                                    if p_child_elem.tagName() == "p":
                                        str_indices = p_child_elem.firstChild().toText().data().split(" ")
                                        index_array = list(map(int, str_indices))
                                    p_child_elem = p_child_elem.nextSiblingElement()
                            mesh_child_elem = mesh_child_elem.nextSiblingElement()
            dae_elem = dae_elem.nextSiblingElement()
        # print(vert_pos_array)
        # print(normal_array)
        # print(tex_coord_array)
        # print(index_array)
        
        num_of_attributes = 3
        vert_positions = []
        normals = []
        tex_coords = []
        for i in range(0, len(index_array), num_of_attributes):
            vert_pos_index = index_array[i + 0]
            vert_positions.append(vert_pos_array[vert_pos_index * 3 + 0])
            vert_positions.append(vert_pos_array[vert_pos_index * 3 + 1])
            vert_positions.append(vert_pos_array[vert_pos_index * 3 + 2])
            
            normal_index = index_array[i + 1]
            normals.append(normal_array[normal_index * 3 + 0])
            normals.append(normal_array[normal_index * 3 + 1])
            normals.append(normal_array[normal_index * 3 + 2])
            
            tex_coord_index = index_array[i + 2]
            tex_coords.append(tex_coord_array[tex_coord_index * 2 + 0])
            tex_coords.append(tex_coord_array[tex_coord_index * 2 + 1])
        # print(vert_positions)
        # print(normals)
        # print(tex_coords)
        
        output = {}

        vert_positions = np.array(vert_positions, dtype=np.float32)
        vert_pos_buffer = QOpenGLBuffer()
        vert_pos_buffer.create()
        vert_pos_buffer.bind()
        vert_pos_buffer.allocate(vert_positions, len(vert_positions) * 4)
        
        normals = np.array(normals, dtype=np.float32)
        normal_buffer = QOpenGLBuffer()
        normal_buffer.create()
        normal_buffer.bind()
        normal_buffer.allocate(normals, len(normals) * 4)
        
        tex_coords = np.array(tex_coords, dtype=np.float32)
        tex_coord_buffer = QOpenGLBuffer()
        tex_coord_buffer.create()
        tex_coord_buffer.bind()
        tex_coord_buffer.allocate(tex_coords, len(tex_coords) * 4)

        vert_buffers = VertexBuffers()
        vert_buffers.vert_pos_buffer = vert_pos_buffer
        vert_buffers.normal_buffer = normal_buffer
        vert_buffers.tex_coord_buffer = tex_coord_buffer
        vert_buffers.amount_of_vertices = int(len(index_array) / 3)
        
        return vert_buffers

def main():
    QApplication.setAttribute(Qt.AA_UseDesktopOpenGL)
    app = QApplication(sys.argv)
    w = Window()
    w.show()
    sys.exit(app.exec_())

if __name__ == "__main__":
    main()

PySide2:

import sys
import numpy as np
from OpenGL import GL as gl
from PySide2.QtWidgets import QApplication, QOpenGLWidget
from PySide2.QtGui import QOpenGLShaderProgram, QOpenGLShader, QOpenGLBuffer
from PySide2.QtGui import QOpenGLTexture, QImage
from PySide2.QtGui import QMatrix4x4, QVector3D, QQuaternion
from PySide2.QtXml import QDomDocument, QDomElement
from PySide2.QtCore import Qt, QFile, QIODevice
from PySide2.QtCore import QTimer, QElapsedTimer

from panda3d.bullet import BulletWorld
from panda3d.core import TransformState, Vec3, Quat, Point3
from panda3d.bullet import BulletBoxShape
from panda3d.bullet import BulletRigidBodyNode

# Assets:
# Cube Texture: https://dl.dropboxusercontent.com/s/tply9ubx3n3ycvv/cube.png
# Cube Model: https://dl.dropboxusercontent.com/s/0aktc37c3nx9iq3/cube.dae
# Plane Texture: https://dl.dropboxusercontent.com/s/3iibsnvyw0vupby/plane.png
# Plane Model: https://dl.dropboxusercontent.com/s/e0wktg69ec3w8pq/plane.dae

class VertexBuffers:
    vertex_pos_buffer = None
    normal_buffer = None
    tex_coord_buffer = None
    amount_of_vertices = None

class Locations:
    mvp_matrix_location = None
    model_matrix_location = None
    normal_matrix_location = None

class Object3D:
    position = QVector3D(0, 0, 0)
    rotation = QVector3D(0, 0, 0)
    scale = QVector3D(1, 1, 1)
    mvp_matrix = QMatrix4x4()
    model_matrix = QMatrix4x4()
    normal_matrix = QMatrix4x4()

    def __init__(self, vert_buffers, locations, texture, world, mass, pos):
        self.vert_pos_buffer = vert_buffers.vert_pos_buffer
        self.normal_buffer = vert_buffers.normal_buffer
        self.tex_coord_buffer = vert_buffers.tex_coord_buffer
        self.amount_of_vertices = vert_buffers.amount_of_vertices
        
        self.mvp_matrix_location = locations.mvp_matrix_location
        self.model_matrix_location = locations.model_matrix_location
        self.normal_matrix_location = locations.normal_matrix_location
        
        self.texture = texture

        self.shape = BulletBoxShape(Vec3(0.5, 0.5, 0.5))
        self.node = BulletRigidBodyNode('Box')

        self.position = pos
        self.mass = mass
        self.node.setMass(self.mass)

        p = Point3(self.position.x(), self.position.y(), self.position.z())
        q = Quat.identQuat()
        s = Vec3(1, 1, 1)

        self.transform = TransformState.make_pos_quat_scale(p, q, s)
        self.node.setTransform(self.transform)

        self.node.addShape(self.shape)
        self.world = world
        self.world.attachRigidBody(self.node)

    def draw(self, program, proj_view_matrix):
        program.bind()

        self.vert_pos_buffer.bind()
        program.setAttributeBuffer(0, gl.GL_FLOAT, 0, 3)
        program.enableAttributeArray(0)

        self.normal_buffer.bind()
        program.setAttributeBuffer(1, gl.GL_FLOAT, 0, 3)
        program.enableAttributeArray(1)

        self.tex_coord_buffer.bind()
        program.setAttributeBuffer(2, gl.GL_FLOAT, 0, 2)
        program.enableAttributeArray(2)

        self.position.setX(self.node.getTransform().pos.x)
        self.position.setY(self.node.getTransform().pos.y)
        self.position.setZ(self.node.getTransform().pos.z)
        hpr = self.node.getTransform().getHpr()
        pandaQuat = Quat()
        pandaQuat.setHpr(hpr)
        quat = QQuaternion(pandaQuat.getX(), pandaQuat.getY(), pandaQuat.getZ(), pandaQuat.getW())
        
        self.model_matrix.setToIdentity()
        self.model_matrix.translate(self.position)
        self.model_matrix.rotate(quat)
        self.model_matrix.scale(self.scale)
        self.mvp_matrix = proj_view_matrix * self.model_matrix
        
        self.normal_matrix = self.model_matrix.inverted()
        self.normal_matrix = self.normal_matrix[0].transposed()
        
        program.bind()
        program.setUniformValue(self.mvp_matrix_location, self.mvp_matrix)
        program.setUniformValue(self.model_matrix_location, self.model_matrix)
        program.setUniformValue(self.normal_matrix_location, self.normal_matrix)
        
        self.texture.bind()

        gl.glDrawArrays(gl.GL_TRIANGLES, 0, self.amount_of_vertices)

class Window(QOpenGLWidget):

    def __init__(self):
        super().__init__()
        self.setWindowTitle("Bullet Physics")
        self.resize(268, 268)

    def initializeGL(self):
        gl.glClearColor(0.2, 0.2, 0.2, 1)
        gl.glEnable(gl.GL_DEPTH_TEST)
        vertShaderSrc = """
            #version 330 core

            in vec4 aPosition;
            in vec4 aNormal;
            in vec2 aTexCoord;

            uniform mat4 uMvpMatrix;
            uniform mat4 uModelMatrix;
            uniform mat4 uNormalMatrix;

            out vec3 vPosition;
            out vec3 vNormal;
            out vec2 vTexCoord;

            void main()
            {
                gl_Position = uMvpMatrix * aPosition;
                vPosition = vec3(uModelMatrix * aPosition);
                vNormal = normalize(vec3(uNormalMatrix * aNormal));
                vTexCoord = aTexCoord;
            }
        """
        fragShaderSrc = """
            #version 330 core

            const vec3 lightColor = vec3(0.8, 0.8, 0.8);
            const vec3 lightPosition = vec3(5.0, 7.0, 2.0);
            const vec3 ambientLight = vec3(0.3, 0.3, 0.3);

            uniform sampler2D uSampler;

            in vec3 vPosition;
            in vec3 vNormal;
            in vec2 vTexCoord;

            void main()
            {
                vec4 color = texture2D(uSampler, vTexCoord);
                vec3 normal = normalize(vNormal);
                vec3 lightDirection = normalize(lightPosition - vPosition);
                float nDotL = max(dot(lightDirection, normal), 0.0);
                vec3 diffuse = lightColor * color.rgb * nDotL;
                vec3 ambient = ambientLight * color.rgb;
                gl_FragColor = vec4(diffuse + ambient, color.a);
            }
        """
        self.program = QOpenGLShaderProgram()
        self.program.addShaderFromSourceCode(QOpenGLShader.Vertex, vertShaderSrc)
        self.program.addShaderFromSourceCode(QOpenGLShader.Fragment, fragShaderSrc)
        self.program.link()
        self.program.bind()
        self.program.bindAttributeLocation("aPosition", 0)
        self.program.bindAttributeLocation("aNormal", 1)
        self.program.bindAttributeLocation("aTexCoord", 2)
        locations = Locations()
        self.program.bind()
        locations.mvp_matrix_location = self.program.uniformLocation("uMvpMatrix")
        locations.model_matrix_location = self.program.uniformLocation("uModelMatrix")
        locations.normal_matrix_location = self.program.uniformLocation("uNormalMatrix")
        self.vert_buffers = self.initVertexBuffers("assets/cube.dae")
        self.proj_view_matrix = QMatrix4x4()
        self.proj_matrix = QMatrix4x4()
        self.view_matrix = QMatrix4x4()
        self.view_matrix.lookAt(
            QVector3D(2, 3, 5),
            QVector3D(0, 0, 0),
            QVector3D(0, 1, 0))
        
        self.texture = QOpenGLTexture(QOpenGLTexture.Target2D)
        self.texture.create()
        self.texture.setData(QImage("assets/cube.png"))
        self.texture.setMinMagFilters(QOpenGLTexture.Linear, QOpenGLTexture.Linear)
        self.texture.setWrapMode(QOpenGLTexture.ClampToEdge)

        self.world = BulletWorld()
        self.world.setGravity(Vec3(0, -9.81, 0))

        self.obj = Object3D(self.vert_buffers, locations, self.texture, self.world, mass=0, pos=QVector3D(0, -3, 0))
        self.obj2 = Object3D(self.vert_buffers, locations, self.texture, self.world, mass=1, pos=QVector3D(0.8, 3, 0))
        
        #self.move_dir = 1 # move direction: 1 - up, -1 - down
        #self.move_speed = 0.002
        
        self.timer = QTimer()
        self.timer.timeout.connect(self.animationLoop)
        self.elapsed_timer = QElapsedTimer()
        self.elapsed_timer.start()
        self.delta_time = 0
        self.timer.start(1000/60)
        
    def animationLoop(self):
        self.delta_time = self.elapsed_timer.elapsed()
        self.elapsed_timer.restart()
        self.world.doPhysics(self.delta_time / 1000)
        self.update()
        
    def paintGL(self):
        gl.glClear(gl.GL_COLOR_BUFFER_BIT | gl.GL_DEPTH_BUFFER_BIT)
        self.proj_view_matrix = self.proj_matrix * self.view_matrix
        self.obj.draw(self.program, self.proj_view_matrix)
        self.obj2.draw(self.program, self.proj_view_matrix)

    def resizeGL(self, w, h):
        gl.glViewport(0, 0, w, h)
        self.proj_matrix.setToIdentity()
        self.proj_matrix.perspective(50, float(w) / float(h), 0.1, 100)
        
    def initVertexBuffers(self, path):
        xml_doc = QDomDocument()
        file = QFile(path)
        if not file.open(QIODevice.ReadOnly):
            print("Failed to open the file: " + path)
        xml_doc.setContent(file)
        file.close()
        
        vert_pos_array = []
        normal_array = []
        tex_coord_array = []
        index_array = []
        
        root = xml_doc.documentElement()
        dae_elem = root.firstChildElement()
        while not dae_elem.isNull():
            if dae_elem.tagName() == "library_geometries":
                geom_elem = dae_elem.firstChildElement()
                if geom_elem.tagName() == "geometry":
                    mesh_elem = geom_elem.firstChildElement()
                    if mesh_elem.tagName() == "mesh":
                        mesh_child_elem = mesh_elem.firstChildElement()
                        while not mesh_child_elem.isNull():
                            float_array_elem = mesh_child_elem.firstChildElement()
                            str_array = float_array_elem.firstChild().toText().data().split(" ")
                            if mesh_child_elem.attribute("id").endswith("-mesh-positions"):
                                vert_pos_array = list(map(float, str_array))
                            if mesh_child_elem.attribute("id").endswith("-mesh-normals"):
                                normal_array = list(map(float, str_array))
                            if mesh_child_elem.attribute("id").endswith("-mesh-map-0"):
                                tex_coord_array = list(map(float, str_array))
                            if mesh_child_elem.tagName() == "triangles" or mesh_child_elem.tagName() == "polylist":
                                p_child_elem = mesh_child_elem.firstChildElement()
                                while not p_child_elem.isNull():
                                    if p_child_elem.tagName() == "p":
                                        str_indices = p_child_elem.firstChild().toText().data().split(" ")
                                        index_array = list(map(int, str_indices))
                                    p_child_elem = p_child_elem.nextSiblingElement()
                            mesh_child_elem = mesh_child_elem.nextSiblingElement()
            dae_elem = dae_elem.nextSiblingElement()
        # print(vert_pos_array)
        # print(normal_array)
        # print(tex_coord_array)
        # print(index_array)
        
        num_of_attributes = 3
        vert_positions = []
        normals = []
        tex_coords = []
        for i in range(0, len(index_array), num_of_attributes):
            vert_pos_index = index_array[i + 0]
            vert_positions.append(vert_pos_array[vert_pos_index * 3 + 0])
            vert_positions.append(vert_pos_array[vert_pos_index * 3 + 1])
            vert_positions.append(vert_pos_array[vert_pos_index * 3 + 2])
            
            normal_index = index_array[i + 1]
            normals.append(normal_array[normal_index * 3 + 0])
            normals.append(normal_array[normal_index * 3 + 1])
            normals.append(normal_array[normal_index * 3 + 2])
            
            tex_coord_index = index_array[i + 2]
            tex_coords.append(tex_coord_array[tex_coord_index * 2 + 0])
            tex_coords.append(tex_coord_array[tex_coord_index * 2 + 1])
        # print(vert_positions)
        # print(normals)
        # print(tex_coords)
        
        output = {}

        vert_positions = np.array(vert_positions, dtype=np.float32)
        vert_pos_buffer = QOpenGLBuffer()
        vert_pos_buffer.create()
        vert_pos_buffer.bind()
        vert_pos_buffer.allocate(vert_positions, len(vert_positions) * 4)
        
        normals = np.array(normals, dtype=np.float32)
        normal_buffer = QOpenGLBuffer()
        normal_buffer.create()
        normal_buffer.bind()
        normal_buffer.allocate(normals, len(normals) * 4)
        
        tex_coords = np.array(tex_coords, dtype=np.float32)
        tex_coord_buffer = QOpenGLBuffer()
        tex_coord_buffer.create()
        tex_coord_buffer.bind()
        tex_coord_buffer.allocate(tex_coords, len(tex_coords) * 4)

        vert_buffers = VertexBuffers()
        vert_buffers.vert_pos_buffer = vert_pos_buffer
        vert_buffers.normal_buffer = normal_buffer
        vert_buffers.tex_coord_buffer = tex_coord_buffer
        vert_buffers.amount_of_vertices = int(len(index_array) / 3)
        
        return vert_buffers

def main():
    QApplication.setAttribute(Qt.AA_UseDesktopOpenGL)
    app = QApplication(sys.argv)
    w = Window()
    w.show()
    sys.exit(app.exec_())

if __name__ == "__main__":
    main()
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