ep06_rotating_cube.py

import glfw
from OpenGL.GL import *
from OpenGL.GL.shaders import compileProgram, compileShader
import numpy as np
import pyrr

vertex_src = """
# version 330

layout(location = 0) in vec3 a_position;
layout(location = 1) in vec3 a_color;

uniform mat4 rotation;

out vec3 v_color;

void main()
{
    gl_Position = rotation * vec4(a_position, 1.0);
    v_color = a_color;
}
"""

fragment_src = """
# version 330

in vec3 v_color;
out vec4 out_color;

void main()
{
    out_color = vec4(v_color, 1.0);
}
"""

def window_resize(window, width, height):
    glViewport(0, 0, width, height)

# initializing glfw library
if not glfw.init():
    raise Exception("glfw can not be initialized!")

# creating the window
window = glfw.create_window(1280, 720, "My OpenGL window", None, None)

# check if window was created
if not window:
    glfw.terminate()
    raise Exception("glfw window can not be created!")

# set window's position
glfw.set_window_pos(window, 400, 200)

# set the callback function for window resize
glfw.set_window_size_callback(window, window_resize)

# make the context current
glfw.make_context_current(window)

vertices = [-0.5, -0.5, 0.5, 1.0, 0.0, 0.0,
             0.5, -0.5, 0.5, 0.0, 1.0, 0.0,
             0.5,  0.5, 0.5, 0.0, 0.0, 1.0,
            -0.5,  0.5, 0.5, 1.0, 1.0, 1.0,

            -0.5, -0.5, -0.5, 1.0, 0.0, 0.0,
             0.5, -0.5, -0.5, 0.0, 1.0, 0.0,
             0.5,  0.5, -0.5, 0.0, 0.0, 1.0,
            -0.5,  0.5, -0.5, 1.0, 1.0, 1.0]

indices = [0, 1, 2, 2, 3, 0,
           4, 5, 6, 6, 7, 4,
           4, 5, 1, 1, 0, 4,
           6, 7, 3, 3, 2, 6,
           5, 6, 2, 2, 1, 5,
           7, 4, 0, 0, 3, 7]

vertices = np.array(vertices, dtype=np.float32)
indices = np.array(indices, dtype=np.uint32)

shader = compileProgram(compileShader(vertex_src, GL_VERTEX_SHADER), compileShader(fragment_src, GL_FRAGMENT_SHADER))

# Vertex Buffer Object
VBO = glGenBuffers(1)
glBindBuffer(GL_ARRAY_BUFFER, VBO)
glBufferData(GL_ARRAY_BUFFER, vertices.nbytes, vertices, GL_STATIC_DRAW)

# Element Buffer Object
EBO = glGenBuffers(1)
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO)
glBufferData(GL_ELEMENT_ARRAY_BUFFER, indices.nbytes, indices, GL_STATIC_DRAW)

glEnableVertexAttribArray(0)
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 24, ctypes.c_void_p(0))

glEnableVertexAttribArray(1)
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 24, ctypes.c_void_p(12))

glUseProgram(shader)
glClearColor(0, 0.1, 0.1, 1)
glEnable(GL_DEPTH_TEST)

rotation_loc = glGetUniformLocation(shader, "rotation")

# the main application loop
while not glfw.window_should_close(window):
    glfw.poll_events()

    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT)

    rot_x = pyrr.Matrix44.from_x_rotation(0.5 * glfw.get_time())
    rot_y = pyrr.Matrix44.from_y_rotation(0.8 * glfw.get_time())

    # glUniformMatrix4fv(rotation_loc, 1, GL_FALSE, rot_x * rot_y)
    # glUniformMatrix4fv(rotation_loc, 1, GL_FALSE, rot_x @ rot_y)
    glUniformMatrix4fv(rotation_loc, 1, GL_FALSE, pyrr.matrix44.multiply(rot_x, rot_y))

    glDrawElements(GL_TRIANGLES, len(indices), GL_UNSIGNED_INT, None)

    glfw.swap_buffers(window)

# terminate glfw, free up allocated resources
glfw.terminate()