如何在PyOpenGL中使用顶点数组对象和glDrawElements进行绘制 [英] How to draw with Vertex Array Objects and glDrawElements in PyOpenGL

问题描述

我有以下代码，应该在屏幕上简单地绘制一个绿色三角形.它使用顶点数组对象和索引缓冲区进行绘制，并且具有我能制作的最简单的着色器.

I have the following code which should simply draw a green triangle to the screen. It is using Vertex Array Objects and index buffers to draw and has the simplest shader I could make.

起初，我不使用索引缓冲区，而只是使用glDrawArrays进行绘图调用，它可以正常工作，但是当我将其更改为使用glDrawElements时，则屏幕上没有任何内容(全黑). /p>

At first I was not using index buffers and was simply making the draw call with glDrawArrays which worked fine but when I change it to use glDrawElements then nothing is drawn to the screen (it is entirely black).

from OpenGL.GL import shaders
from OpenGL.arrays import vbo
from OpenGL.GL import *
from OpenGL.raw.GL.ARB.vertex_array_object import glGenVertexArrays, \
                                                  glBindVertexArray

import pygame

import numpy as np

def run():
    pygame.init()
    screen = pygame.display.set_mode((800,600), pygame.OPENGL)

    #Create the Vertex Array Object
    vertexArrayObject = GLuint(0)
    glGenVertexArrays(1, vertexArrayObject)
    glBindVertexArray(vertexArrayObject)

    #Create the VBO
    vertices = np.array([[0,1,0],[-1,-1,0],[1,-1,0]], dtype='f')
    vertexPositions = vbo.VBO(vertices)

    #Create the index buffer object
    indices = np.array([0,1,2], dtype='uint16')
    indexPositions = vbo.VBO(indices, target=GL_ELEMENT_ARRAY_BUFFER)

    indexPositions.bind()
    vertexPositions.bind()

    glEnableVertexAttribArray(0) # from 'location = 0' in shader
    glVertexAttribPointer(0, 3, GL_FLOAT, False, 0, None)

    glBindVertexArray(0)
    vertexPositions.unbind()
    indexPositions.unbind()

    #Now create the shaders
    VERTEX_SHADER = shaders.compileShader("""
    #version 330
    layout(location = 0) in vec4 position;
    void main()
    {
        gl_Position = position;
    }
    """, GL_VERTEX_SHADER)

    FRAGMENT_SHADER = shaders.compileShader("""
    #version 330
    out vec4 outputColor;
    void main()
    {
        outputColor = vec4(0.0f, 1.0f, 0.0f, 1.0f);
    }
    """, GL_FRAGMENT_SHADER)

    shader = shaders.compileProgram(VERTEX_SHADER, FRAGMENT_SHADER)

    #The draw loop
    while True:
        glUseProgram(shader)
        glBindVertexArray(vertexArrayObject)

        #glDrawArrays(GL_TRIANGLES, 0, 3) #This line works
        glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_INT, 0) #This line does not

        glBindVertexArray(0)
        glUseProgram(0)

        # Show the screen
        pygame.display.flip()

run()

如果我只注释掉glDrawElements并取消注释glDrawArrays行，则它可以正常工作，因此至少可以正确输入顶点VBO.

If I simply comment out the glDrawElements and uncomment the glDrawArrays line then it works correctly so at least the vertex VBO is being input correctly.

我在这里做错了什么?我能够找到的所有OpenGL文档都表明我正确地执行了此操作，因此很明显我对OpenGL本身或PyOpenGL包装程序有误解.

What am I doing wrong here? All the OpenGL documentation I have been able to find suggests that I am doing this correctly so I am obviously misunderstanding something either about OpenGL itself or the PyOpenGL wrapper.

编辑

更改VAO设置以使用更直接的OpenGL函数，而不是像这样的VBO包装器:

Changing the VAO setup to use more direct OpenGL function rather than the VBO wrapper like:

vertices = np.array([[0,1,0],[-1,-1,0],[1,-1,0]], dtype='f')
vertexPositions = glGenBuffers(1)
glBindBuffer(GL_ARRAY_BUFFER, vertexPositions)
glBufferData(GL_ARRAY_BUFFER, vertices, GL_STATIC_DRAW)

#Create the index buffer object
indices = np.array([0,1,2], dtype='uint16')
indexPositions = glGenBuffers(1)
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexPositions)
glBufferData(GL_ELEMENT_ARRAY_BUFFER, indices, GL_STATIC_DRAW)

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexPositions)
glBindBuffer(GL_ARRAY_BUFFER, vertexPositions)

glEnableVertexAttribArray(0) # from 'location = 0' in shader
glVertexAttribPointer(0, 3, GL_FLOAT, False, 0, None)

glBindVertexArray(0)
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0)
glBindBuffer(GL_ARRAY_BUFFER, 0)

没有区别. glDrawArrays仍然有效，而glDrawElements仍然无效.

makes no difference. glDrawArrays still works and glDrawElements still doesn't.

推荐答案

感谢@NicolBolas.他激励我真正采用此代码并使之生效.而不是理论化:) 我已经删除了vertexArrayObject(它是多余的，因为我们已经有用于顶点和索引的VBO). 因此，您只需在调用glDraw *之前绑定索引和顶点缓冲区(以及属性)即可. 当然，将None(空指针)传递给glDrawElements索引而不是0非常重要！

Thanks @NicolBolas. He motivated me to actually take this code and make it work. Instead of theoritizing:) I have removed vertexArrayObject(it's redundand as we already have VBOs for vertices and indices). So you just bind index and vertex buffers(along with attributes) prior to glDraw* call. And of course very important to pass None(null pointer) to glDrawElements indices instead of 0!

from OpenGL.GL import shaders
from OpenGL.arrays import vbo
from OpenGL.GL import *
from OpenGL.raw.GL.ARB.vertex_array_object import glGenVertexArrays, \
                                                  glBindVertexArray

import pygame

import numpy as np

def run():
    pygame.init()
    screen = pygame.display.set_mode((800,600), pygame.OPENGL|pygame.DOUBLEBUF)

    #Create the VBO
    vertices = np.array([[0,1,0],[-1,-1,0],[1,-1,0]], dtype='f')
    vertexPositions = vbo.VBO(vertices)

    #Create the index buffer object
    indices = np.array([[0,1,2]], dtype=np.int32)
    indexPositions = vbo.VBO(indices, target=GL_ELEMENT_ARRAY_BUFFER)

    #Now create the shaders
    VERTEX_SHADER = shaders.compileShader("""
    #version 330
    layout(location = 0) in vec4 position;
    void main()
    {
        gl_Position = position;
    }
    """, GL_VERTEX_SHADER)

    FRAGMENT_SHADER = shaders.compileShader("""
    #version 330
    out vec4 outputColor;
    void main()
    {
        outputColor = vec4(0.0f, 1.0f, 0.0f, 1.0f);
    }
    """, GL_FRAGMENT_SHADER)

    shader = shaders.compileProgram(VERTEX_SHADER, FRAGMENT_SHADER)

    #The draw loop
    while True:
        glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT)
        glUseProgram(shader)

        indexPositions.bind()

        vertexPositions.bind()
        glEnableVertexAttribArray(0);
        glVertexAttribPointer(0, 3, GL_FLOAT, False, 0, None)

        #glDrawArrays(GL_TRIANGLES, 0, 3) #This line still works
        glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_INT, None) #This line does work too!

        # Show the screen
        pygame.display.flip()

run()

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