基于Python的OpenGL 04 之变换

1. 概述

本文基于Python语言，描述OpenGL的变换

前置知识可参考：

• 基于Python的OpenGL 03 之纹理 - 当时明月在曾照彩云归 - 博客园 (cnblogs.com)

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：

• 变换 - LearnOpenGL CN (learnopengl-cn.github.io)

2. 导入GLM

平移、旋转、缩放等变换主要是使用变换矩阵来实现

OpenGL Mathematics(GLM)是一个基于GLSL的只有头文件的C++数学运算库

GLM的GitHub站点为：g-truc/glm: OpenGL Mathematics (GLM) (github.com)

PyGLM是GLM的Python绑定，其API基本一致

PyGLM的GitHub站点为：Zuzu-Typ/PyGLM: Fast OpenGL Mathematics (GLM) for Python (github.com)

PyGLM的PyPi地址为：PyGLM · PyPI

使用pip安装PyGLM：

pip install PyGLM

引入GLM：

import glm

3. 设置变换矩阵

设置一个平移、旋转、缩放的矩阵：

trans = glm.mat4(1.0)
trans = glm.translate(trans, glm.vec3(0.5, -0.5, 0.0)*np.sin(glfw.get_time()))
trans = glm.rotate(trans, glfw.get_time(), glm.vec3(0.0, 0.0, 1.0))
trans = glm.scale(trans, glm.vec3(1.0, 1.0, 0.0)*(np.sin(glfw.get_time())*0.5+0.5))

在顶点着色器中将变换矩阵与坐标结合：

#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec3 aColor;
layout (location = 2) in vec2 aTexCoord;

out vec3 ourColor;
out vec2 TexCoord;

uniform mat4 transform;

void main()
{
    gl_Position = transform * vec4(aPos, 1.0);
    ourColor = aColor;
    TexCoord = aTexCoord;
}

将变换矩阵输入到GPU：

glUniformMatrix4fv(glGetUniformLocation(shader.shaderProgram, 'transform'), 1, GL_FALSE, glm.value_ptr(trans))

如果顺利的话，结果如下：

4. 完整代码

主要文件test.py：

import glfw as glfw
from OpenGL.GL import *
import numpy as np
from PIL.Image import open
import glm as glm

import shader as shader

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

VAO = glGenVertexArrays(1)
glBindVertexArray(VAO)

vertices = np.array([
     # ---- 位置 ----       ---- 颜色 ----     - 纹理坐标 -
     0.5,  0.5, 0.0,   1.0, 0.0, 0.0,   1.0, 1.0,   # 右上
     0.5, -0.5, 0.0,   0.0, 1.0, 0.0,   1.0, 0.0,   # 右下
    -0.5, -0.5, 0.0,   0.0, 0.0, 1.0,   0.0, 0.0,   # 左下
    -0.5,  0.5, 0.0,   1.0, 1.0, 0.0,   0.0, 1.0,   # 左上
                    ])
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 * 8), None)
glEnableVertexArrayAttrib(VAO, 0)
glVertexAttribPointer(1, 3, GL_DOUBLE, GL_FALSE, int(8 * 8), ctypes.c_void_p(8 * 3))
glEnableVertexArrayAttrib(VAO, 1)
glVertexAttribPointer(2, 2, GL_DOUBLE, GL_FALSE, int(8 * 8), ctypes.c_void_p(8 * 6))
glEnableVertexAttribArray(2)

indices = np.array([
        0, 1, 3,  # first triangle
        1, 2, 3  # second triangle
        ])
EBO = glGenBuffers(1)
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO)
glBufferData(GL_ELEMENT_ARRAY_BUFFER, 8 * indices.size, indices, GL_STATIC_DRAW)

image = open('./textures/container.jpg')
texture = glGenTextures(1)
glBindTexture(GL_TEXTURE_2D, texture)
# 为当前绑定的纹理对象设置环绕、过滤方式
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR)
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, image.size[0], image.size[1], 0, GL_RGB, GL_UNSIGNED_BYTE, image.tobytes())
glGenerateMipmap(GL_TEXTURE_2D)

shader = shader.Shader("./glsl/test.vs.glsl", "./glsl/test.fs.glsl")

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

    trans = glm.mat4(1.0)
    trans = glm.translate(trans, glm.vec3(0.5, -0.5, 0.0)*np.sin(glfw.get_time()))
    trans = glm.rotate(trans, glfw.get_time(), glm.vec3(0.0, 0.0, 1.0))
    trans = glm.scale(trans, glm.vec3(1.0, 1.0, 0.0)*(np.sin(glfw.get_time())*0.5+0.5))

    shader.use()
    glUniformMatrix4fv(glGetUniformLocation(shader.shaderProgram, 'transform'), 1, GL_FALSE, glm.value_ptr(trans))

    glBindVertexArray(VAO)
    glActiveTexture(GL_TEXTURE0)  # 在绑定纹理之前先激活纹理单元
    glBindTexture(GL_TEXTURE_2D, texture)
    # glDrawArrays(GL_TRIANGLES, 0, 3)
    glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, None)

    glfw.swap_buffers(window)
    glfw.poll_events()

shader.delete()

顶点着色器test.vs.glsl：

#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec3 aColor;
layout (location = 2) in vec2 aTexCoord;

out vec3 ourColor;
out vec2 TexCoord;

uniform mat4 transform;

void main()
{
    gl_Position = transform * vec4(aPos, 1.0);
    ourColor = aColor;
    TexCoord = aTexCoord;
}

片段着色器test.fs.glsl：

#version 330 core
out vec4 FragColor;

in vec3 ourColor;
in vec2 TexCoord;

uniform sampler2D texture1;
uniform sampler2D texture2;

void main()
{
    FragColor = mix(texture(texture1, TexCoord), texture(texture2, TexCoord), 0.2);
}

• shader.py见：基于Python的OpenGL 02 之着色器 - 当时明月在曾照彩云归 - 博客园 (cnblogs.com)

5. 参考资料

[1]变换 - LearnOpenGL CN (learnopengl-cn.github.io)

[2]glm/manual.md at master · g-truc/glm (github.com)

[3]OpenGL学习笔记三——引入GLM库，实现transform_绿洲守望者的博客-CSDN博客_glm库

[4]OpenGL学习笔记（五）纹理 - 知乎 (zhihu.com)

[5]PyGLM · PyPI

[6]LearnOpenGL-Python/transformations.py at master · Zuzu-Typ/LearnOpenGL-Python (github.com)