一、目的

1、使用GLSL实现图形的平移。

二、程序运行结果

三、平移变换

  平移变换的任务是将一个对象沿着一个任意长度和方向的向量移动。
  对于三维空间上的一点(x,y,z)，我们使用4*4齐次矩阵的形式来表示平移变换：

translation transformation

  使用四维向量来表示三维向量的做法称作齐次坐标，这对3D图形学来说普遍而又实用。向量的第四个分量称之为 “w” 。事实上，我们在以前教程中见到的着色器中的内置变量 gl_Position 就是一个四维向量，w 分量会在将3D场景投影到 2D 平面时起重要作用！通用的做法是： w = 1 时表示点，w = 0 时表示向量。原因是点可以被平移但是向量不行，你可以改变向量的长度和方向，但是无论向量的起点在哪里，所有具有相同长度和方向的向量是被视为相同的！所以你可以简单地用原点作为所有向量的起点！当我们将 w 设置为0时，乘以变换矩阵后的向量还会是相同的向量。

四、代码解析

1、在GLSL程序中，建立一个4*4齐次矩阵dot，将该矩阵与每个点相乘可得到x,y坐标都平移scare的新点坐标。
2、向量vec4(scale,scale,0.0,1.0)表示的是第4列，矩阵运算后，点(x,y)移到(x+scale,y+scale)处

五、源代码

"""
glfw_square02.py
Author: dalong10
Description: Draw a Square, learning OPENGL 
"""
import glutils    #Common OpenGL utilities,see glutils.py
import sys, random, math
import OpenGL
from OpenGL.GL import *
from OpenGL.GL.shaders import *
import numpy 
import numpy as np
import glfw

strVS = """
#version 330 core
layout(location = 0) in vec3 position;
uniform float scale;

void main(){
    mat4 rot=mat4(vec4(1.0, 0.0,0.0,0),
                vec4(0.0, 1.0,0.0,0),
                vec4(0.0,0.0,1.0,0.0),
                vec4(scale,scale,0.0,1.0));
    gl_Position=rot * vec4(position.x, position.y, position.z, 1.0);
    
    }
"""

strFS = """
#version 330 core
out vec3 color;
void main(){
    color = vec3(1,1,0);
    }
"""

class FirstSquare:
    def __init__(self, side):
        self.side = side

        # load shaders
        self.program = glutils.loadShaders(strVS, strFS)
        glUseProgram(self.program)
        
        s = side/2.0
        vertices = [
            -s, s, 0,  
             s, s, 0,  
             s, -s, 0 , 
             -s, -s, 0            
             ]
                
        # set up vertex array object (VAO)
        self.vao = glGenVertexArrays(1)
        glBindVertexArray(self.vao)
        # set up VBOs
        vertexData = numpy.array(vertices, numpy.float32)
        self.vertexBuffer = glGenBuffers(1)
        glBindBuffer(GL_ARRAY_BUFFER, self.vertexBuffer)
        glBufferData(GL_ARRAY_BUFFER, 4*len(vertexData), vertexData, 
                     GL_STATIC_DRAW)
        #enable arrays
        self.vertIndex = 0
        glEnableVertexAttribArray(self.vertIndex)
        # set buffers 
        glBindBuffer(GL_ARRAY_BUFFER, self.vertexBuffer)
        glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, None)
        # unbind VAO
        glBindVertexArray(0)

    def render(self):       
        # use shader
        glUseProgram(self.program)
        scale = i*0.1
        glUniform1f(glGetUniformLocation(self.program, "scale"), scale)

        # bind VAO
        glBindVertexArray(self.vao)
        # draw
        glDrawArrays(GL_LINE_LOOP, 0, 4)
        # unbind VAO
        glBindVertexArray(0)

if __name__ == '__main__':
    import sys
    import glfw
    import OpenGL.GL as gl
    def on_key(window, key, scancode, action, mods):
        if key == glfw.KEY_ESCAPE and action == glfw.PRESS:
            glfw.set_window_should_close(window,1)

    # Initialize the library
    if not glfw.init():
        sys.exit()

    # Create a windowed mode window and its OpenGL context
    window = glfw.create_window(640, 480, "Square translation transformation", None, None)
    if not window:
        glfw.terminate()
        sys.exit()

    # Make the window's context current
    glfw.make_context_current(window)

    # Install a key handler
    glfw.set_key_callback(window, on_key)

    # Loop until the user closes the window
    while not glfw.window_should_close(window):
        # Render here
        width, height = glfw.get_framebuffer_size(window)
        ratio = width / float(height)
        gl.glViewport(0, 0, width, height)
        gl.glClear(gl.GL_COLOR_BUFFER_BIT)
        gl.glClearColor(0.0,0.0,4.0,0.0)
        firstSquare0 = FirstSquare(1.0)        
        for i in range(-4,4):
            firstSquare0.render()            

        # Swap front and back buffers
        glfw.swap_buffers(window)
        
        # Poll for and process events
        glfw.poll_events()

    glfw.terminate()