基于Python的OpenGL 01 之Hello Triangle

1. 引言

本文基于Python语言,描述OpenGL的绘制流程,这里描述的是OpenGL的核心模式(Core-profile)

本文基于GLFW与PyOpenGL库进行开发,Python语言下的OpenGL环境搭建可参考:

笔者这里不过多描述每个名词、函数和细节,更详细的文档可以参考:

2. 流程综述

OpenGL的绘制流程(图形渲染管线,Graphics Pipeline)如下:

img

  • 顶点着色(vertex shader)阶段将CPU传入的数据进行一定的变换处理
  • 图元装配(shape assembly)阶段的就是上阶段的顶点数据处理成图元(如,三角形)
  • 几何着色(geometry shader)阶段是根据一定规则将输入的图元变更或输出更多的图元(可选)
  • 光栅化(rasterization)阶段的是将上阶段的图元进行计算得到图元占据的屏幕像素列表
  • 片元着色(fragment)阶段是将上阶段生成的片元进行着色处理后
  • 测试与混合阶段计算片元的深度、颜色等从而进行舍弃或保留

绘制流程繁琐,然而,我们能配置的只有三个蓝色的着色器部分。几何着色器可选,一般配置顶点着色器和片段着色器即可,即,以下步骤就是配置顶点着色器和片段着色器

3. 生成顶点数据

生成顶点缓冲对象(Vertex Buffer Objects, VBO)并加载数据:

vertices = np.array([[-0.5, -0.5, 0.0],
                     [0.5, -0.5, 0.0],
                     [0.0, 0.5, 0.0]])
VBO = glGenBuffers(1)
glBindBuffer(GL_ARRAY_BUFFER, VBO)
glBufferData(GL_ARRAY_BUFFER, 8*vertices.size, vertices, GL_STATIC_DRAW)

4. 链接属性数据

顶点数组对象(Vertex Array Object, VAO)与VBO绑定,用于保存属性数据(先绑定VAO,再创建VBO就会绑定到VAO上):

VAO = glGenVertexArrays(1)
glBindVertexArray(VAO)

vertices = np.array([[-0.5, -0.5, 0.0],
                     [0.5, -0.5, 0.0],
                     [0.0, 0.5, 0.0]])
VBO = glGenBuffers(1)
glBindBuffer(GL_ARRAY_BUFFER, VBO)
glBufferData(GL_ARRAY_BUFFER, 8*vertices.size, vertices, GL_STATIC_DRAW)

glVertexAttribPointer(0, 3, GL_DOUBLE, GL_FALSE, int(8*3), None)
glEnableVertexArrayAttrib(VAO, 0)

5. 创建顶点着色器

创建顶点着色器(Vertex Shader)并编译:

vertexShaderSource = """
    #version 330 core
    layout (location = 0) in vec3 aPos;
    
    void main()
    {
        gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);
    }
"""
vertexShader = glCreateShader(GL_VERTEX_SHADER)
glShaderSource(vertexShader, vertexShaderSource)
glCompileShader(vertexShader)

6. 创建片段着色器

创建片段着色器(Fragment Shader)并编译:

fragmentShaderSource = """
    #version 330 core
    out vec4 FragColor;
    
    void main()
    {
        FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);
    } 
"""
fragmentShader = glCreateShader(GL_FRAGMENT_SHADER)
glShaderSource(fragmentShader, fragmentShaderSource)
glCompileShader(fragmentShader)

7. 链接着色器

着色器程序对象(Shader Program Object)是多个着色器合并之后并最终链接完成的版本:

shaderProgram = glCreateProgram()
glAttachShader(shaderProgram, vertexShader)
glAttachShader(shaderProgram, fragmentShader)
glLinkProgram(shaderProgram)

8. 绘制

开始(循环)绘制:

glClearColor(0.2, 0.3, 0.3, 1.0);
glClear(GL_COLOR_BUFFER_BIT);

glUseProgram(shaderProgram);
glBindVertexArray(VAO);
glDrawArrays(GL_TRIANGLES, 0, 3);

9. 完整代码

基于GLFW、PyOpenGL和Numpy创建OpenGL开发环境,完整代码如下:

import glfw
from OpenGL.GL import *
import numpy as np

glfw.init()
window = glfw.create_window(800, 600, "hello triangle", None, None)
glfw.make_context_current(window)

VAO = glGenVertexArrays(1)
glBindVertexArray(VAO)

vertices = np.array([[-0.5, -0.5, 0.0],
                     [0.5, -0.5, 0.0],
                     [0.0, 0.5, 0.0]])
VBO = glGenBuffers(1)
glBindBuffer(GL_ARRAY_BUFFER, VBO)
glBufferData(GL_ARRAY_BUFFER, 8*vertices.size, vertices, GL_STATIC_DRAW)
glVertexAttribPointer(0, 3, GL_DOUBLE, GL_FALSE, int(8*3), None)
glEnableVertexArrayAttrib(VAO, 0)

vertexShaderSource = """
    #version 330 core
    layout (location = 0) in vec3 aPos;
    
    void main()
    {
        gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);
    }
"""
vertexShader = glCreateShader(GL_VERTEX_SHADER)
glShaderSource(vertexShader, vertexShaderSource)
glCompileShader(vertexShader)

fragmentShaderSource = """
    #version 330 core
    out vec4 FragColor;
    
    void main()
    {
        FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);
    } 
"""
fragmentShader = glCreateShader(GL_FRAGMENT_SHADER)
glShaderSource(fragmentShader, fragmentShaderSource)
glCompileShader(fragmentShader)

shaderProgram = glCreateProgram()
glAttachShader(shaderProgram, vertexShader)
glAttachShader(shaderProgram, fragmentShader)
glLinkProgram(shaderProgram)

glDeleteShader(vertexShader)
glDeleteShader(fragmentShader)

while not glfw.window_should_close(window):
    glClearColor(0.2, 0.3, 0.3, 1.0)
    glClear(GL_COLOR_BUFFER_BIT)

    glUseProgram(shaderProgram)
    glBindVertexArray(VAO);
    glDrawArrays(GL_LINE_STRIP, 0, 3)
        
    glfw.swap_buffers(window)
    glfw.poll_events()

运行结果如下:

image-20220715233727161

10. 参考资料

[1]你好,三角形 - LearnOpenGL CN (learnopengl-cn.github.io)

[2]【Learn OpenGL笔记】三角形(Triangle) - 知乎 (zhihu.com)

[3]基于GLFW的PyOpenGL的使用 - 当时明月在曾照彩云归 - 博客园 (cnblogs.com)

[4](Python OpenGL)【3】着色器 PyOpenGL - WSX_1994 - 博客园 (cnblogs.com)

posted @ 2022-07-14 23:51  当时明月在曾照彩云归  阅读(439)  评论(0编辑  收藏  举报