Re: [PyOpenGL-Users] How to draw a cube using indices ?

[Florian N. <flo...@en...>]

Yes it solves my problem.

Thanks!
> Le 27 nov. 2015 à 19:19, Nicolas P. Rougier <Nic...@in...> a écrit :
> 
> Maybe you need to use np.uint32 for the dtype of the index array.
> 
> Nicolas
> 
> 
>> On 27 Nov 2015, at 16:20, Florian NICOLAS <flo...@en...> wrote:
>> 
>> Yes it works (ctypes.c_void_p(0) also works). 
>> However, it seems that only half the cube is rendered. It is a bit strange as my vertex and associated indices come from a tutorial.
>> 
>> 
>> 
>> ------------------------------------------------------------------------------------------------------------------------
>> NICOLAS Florian
>> Ingénieur études amont - Service Etudes Générales Sonar
>> THALES Underwater Systems
>> ENSTA Bretagne (ex-ENSIETA) - Promotion 2014 - Spécialité SPID (Système Perception Information Décision)
>> Profil PSO (Perception et Systèmes d'Observation)
>> 
>> ________________________________________
>> De : Nicolas P. Rougier <Nic...@in...>
>> Envoyé : vendredi 27 novembre 2015 16:04
>> À : Florian NICOLAS
>> Cc : pyo...@li...
>> Objet : Re: [PyOpenGL-Users] How to draw a cube using indices ?
>> 
>> You've already bound your index buffer so you don't need to give it as argument.
>> In your display function:
>> 
>> gl.glDrawElements(gl.GL_TRIANGLES, len(index), gl.GL_UNSIGNED_INT, index)
>> 
>> becomes
>> 
>> gl.glDrawElements(gl.GL_TRIANGLES, len(index), gl.GL_UNSIGNED_INT, None)
>> 
>> 
>> 
>> Nicolas
>> 
>> 
>>> On 27 Nov 2015, at 14:57, Florian NICOLAS <flo...@en...> wrote:
>>> 
>>> 
>>> Hi everybody!
>>> 
>>> I recently started to learn OpenGL through Python thanks to several tutorial (especially the Nicolas P. Rougier one: http://www.labri.fr/perso/nrougier/teaching/opengl/).
>>> 
>>> I am now switching to 3D and I am trying to draw a cube.
>>> 
>>> Thus, I manage to get some triangles which do not render a cube (this seems to be normal as I do not duplicate my vertices and I use the glDrawArrays function).
>>> 
>>> However, after, I build an index "vector" to further use the glDrawElements function to render my cube. As a result, I do not get any error but nothing appears on screen.
>>> 
>>> I hope you could be of some help!
>>> 
>>> Thanks.
>>> 
>>> Here is my code:
>>> 
>>> #! /usr/bin/env python
>>> # -*- coding: utf-8 -*-
>>> 
>>> import sys
>>> import ctypes
>>> import numpy as np
>>> import OpenGL.GL as gl
>>> import OpenGL.GLUT as glut
>>> 
>>> vertex_code = """
>>> 
>>>  uniform float scale;
>>>  uniform mat4 matCam;
>>>  attribute vec4 color;
>>>  attribute vec3 position;
>>>  varying vec4 v_color;
>>>  void main()
>>>  {
>>>      gl_Position = matCam*vec4(scale*position, 1.0);
>>>      v_color = color;
>>>  } """
>>> 
>>> fragment_code = """
>>>  varying vec4 v_color;
>>>  void main()
>>>  {
>>>      gl_FragColor = v_color;
>>>  } """
>>> 
>>> def display():
>>>  gl.glClear(gl.GL_COLOR_BUFFER_BIT)
>>>  #gl.glDrawArrays(gl.GL_TRIANGLES, 0, 12)
>>>  gl.glDrawElements(gl.GL_TRIANGLES, len(index), gl.GL_UNSIGNED_INT, index) # render nothing (i.e. only the background color)
>>>  glut.glutSwapBuffers()
>>> 
>>> def reshape(width,height):
>>>  gl.glViewport(0, 0, width, height)
>>> 
>>> def keyboard( key, x, y ):
>>>  if key == '\033':
>>>      sys.exit( )
>>> 
>>> def timer(fps):
>>>  global clock
>>>  clock += 0.0005*1000.0/fps
>>>  print(clock)
>>> #    eye = np.array([0,0,1])
>>> #    center = np.array([0,clock,0])
>>> #    up = np.array([0,1,0])
>>> #    mat = computeLookAtMatrix(eye, center, up)
>>>  theta = clock;
>>>  mat = np.array([[np.cos(theta), 0, np.sin(theta), 0],
>>>              [0, 1, 0, 0],
>>>              [-np.sin(theta), 0, np.cos(theta), 0],
>>>              [0, 0, 0, 1]])
>>>  loc = gl.glGetUniformLocation(program, "matCam")
>>>  gl.glUniformMatrix4fv(loc, 1, False, mat)
>>> 
>>> 
>>> 
>>>  glut.glutTimerFunc(1000/fps, timer, fps)
>>>  glut.glutPostRedisplay()
>>> 
>>> 
>>> # GLUT init
>>> # --------------------------------------
>>> glut.glutInit()
>>> glut.glutInitDisplayMode(glut.GLUT_DOUBLE | glut.GLUT_RGBA)
>>> glut.glutCreateWindow('Hello world!')
>>> glut.glutReshapeWindow(512,512)
>>> glut.glutReshapeFunc(reshape)
>>> glut.glutDisplayFunc(display)
>>> glut.glutKeyboardFunc(keyboard)
>>> glut.glutTimerFunc(1000/60, timer, 60)
>>> 
>>> # Build data
>>> # --------------------------------------
>>> data = np.zeros(8, [("position", np.float32, 3),
>>>                  ("color",    np.float32, 4)])
>>> 
>>> data['color']    = [ (1,0,0,1), (0,1,0,1), (0,0,1,1), (1,1,0,1),
>>>                  (1,0,0,1), (0,1,0,1), (0,0,1,1), (1,1,0,1) ]
>>> 
>>> data['position'] = [ (-1,-1,1),
>>>                   (1,-1,1),
>>>                      (1,1,1),
>>>                      (-1,1,1),
>>>                      (-1,-1,-1),
>>>                      (1,-1,-1),
>>>                      (1,1,-1),
>>>                      (-1,1,-1)]
>>> 
>>> index = np.array([0,1,2,
>>>              2,3,0,
>>>              1,5,6,
>>>              6,2,1,
>>>              7,6,5,
>>>              5,4,7,
>>>              4,0,3,
>>>              3,7,4,
>>>              4,5,1,
>>>              1,0,4,
>>>              3,2,6,
>>>              6,7,3])
>>> 
>>> # Build & activate program
>>> # --------------------------------------
>>> 
>>> # Request a program and shader slots from GPU
>>> program  = gl.glCreateProgram()
>>> vertex   = gl.glCreateShader(gl.GL_VERTEX_SHADER)
>>> fragment = gl.glCreateShader(gl.GL_FRAGMENT_SHADER)
>>> 
>>> # Set shaders source
>>> gl.glShaderSource(vertex, vertex_code)
>>> gl.glShaderSource(fragment, fragment_code)
>>> 
>>> # Compile shaders
>>> gl.glCompileShader(vertex)
>>> gl.glCompileShader(fragment)
>>> 
>>> # Attach shader objects to the program
>>> gl.glAttachShader(program, vertex)
>>> gl.glAttachShader(program, fragment)
>>> 
>>> # Build program
>>> gl.glLinkProgram(program)
>>> 
>>> # Get rid of shaders (no more needed)
>>> gl.glDetachShader(program, vertex)
>>> gl.glDetachShader(program, fragment)
>>> 
>>> # Make program the default program
>>> gl.glUseProgram(program)
>>> 
>>> 
>>> # Build buffer
>>> # --------------------------------------
>>> 
>>> # Request a buffer slot from GPU
>>> buffer = gl.glGenBuffers(1)
>>> 
>>> # Make this buffer the default one
>>> gl.glBindBuffer(gl.GL_ARRAY_BUFFER, buffer)
>>> 
>>> # Upload data
>>> gl.glBufferData(gl.GL_ARRAY_BUFFER, data.nbytes, data, gl.GL_DYNAMIC_DRAW)
>>> 
>>> # same for index buffer
>>> buffer_index= gl.glGenBuffers(1)
>>> gl.glBindBuffer(gl.GL_ELEMENT_ARRAY_BUFFER, buffer_index)
>>> gl.glBufferData(gl.GL_ELEMENT_ARRAY_BUFFER, index.nbytes, index, gl.GL_STATIC_DRAW)
>>> 
>>> 
>>> # Bind attributes
>>> # --------------------------------------
>>> stride = data.strides[0]
>>> offset = ctypes.c_void_p(0)
>>> loc = gl.glGetAttribLocation(program, "position")
>>> gl.glEnableVertexAttribArray(loc)
>>> gl.glBindBuffer(gl.GL_ARRAY_BUFFER, buffer)
>>> gl.glVertexAttribPointer(loc, 3, gl.GL_FLOAT, False, stride, offset)
>>> 
>>> offset = ctypes.c_void_p(data.dtype["position"].itemsize)
>>> loc = gl.glGetAttribLocation(program, "color")
>>> gl.glEnableVertexAttribArray(loc)
>>> gl.glBindBuffer(gl.GL_ARRAY_BUFFER, buffer)
>>> gl.glVertexAttribPointer(loc, 4, gl.GL_FLOAT, False, stride, offset)
>>> 
>>> gl.glBindBuffer(gl.GL_ELEMENT_ARRAY_BUFFER, buffer_index)
>>> 
>>> # Bind uniforms
>>> # --------------------------------------
>>> loc = gl.glGetUniformLocation(program, "scale")
>>> gl.glUniform1f(loc, 0.5)
>>> clock = 0
>>> 
>>> loc = gl.glGetUniformLocation(program, "matCam")
>>> print(loc)
>>> gl.glUniformMatrix4fv(loc, 1, False, np.eye(4))
>>> 
>>> # Enter mainloop
>>> # --------------------------------------
>>> glut.glutMainLoop()
>>> ------------------------------------------------------------------------------
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>> 
>> 
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>