一、目的

1、正弦函數的基本畫法；
2、GLSL方式實現練習。

二、程序運行結果

三、glDrawArrays 函數

??GLSL畫這些基本的類型使用的函數主要是glDraw*系列的函數：

            
              void  glDrawArrays (GLenum mode, GLint first, GLsizei count);

            
          

??mode有以下類型，畫點GL_POINTS，畫線 GL_LINES，順連線段GL_LINE_STRIP，回環線段GL_LINE_LOOP，三角形GL_TRIANGLES，GL_TRIANGLE_STRIP，GL_TRIANGLE_FAN，四邊形GL_QUADS，GL_QUAD_STRIP，多邊形GL_POLYGON。
??first為0即可，
??count表示要繪制頂點的個數。

四、正弦波繪制

??正弦波公式是y = sin(x ) ，通過描點畫出圖形。需確定了以下幾個參數來畫正弦波：
??1. sampleCnt：采樣點個數，openGL畫東西都采用逼近的方式，采樣點越多，正弦波就越精細。
??2. factor：用來控制正弦波的頻率，如sin(2x ),sin(3x ) 等。
??3. amplitude：振幅，用來控制正弦波的振幅，如3sin(2x )。
??4. rangeL：我們要把正弦波映射到[-1.0,1.0]的范圍內,否則畫出來的正弦波都看不到。
??5. rangeR：如傳的-pi~pi的范圍，會把這個范圍的正弦波映射到[-1.0,1.0]范圍內。
??注意：shader里面y坐標統一乘了0.9，主要是避免圖形頂到邊框。

五、源代碼

            
              """
glfw_sin01.py
Author: dalong10
Description: Draw a Sine curve, 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 vec2 position;
void main(){
	gl_Position = vec4(position.x,position.y*0.9,0.0,1.0);
	}
"""

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

def createSinArray(sampleCnt, factor, amplitude, rangeL,rangeR):
    i = 0
    range0 = rangeR-rangeL
    if ((sampleCnt<=4) or (rangeR <= rangeL)):
        print("param error sampleCnt:%d rangeR:%f rangeL:%f\n",sampleCnt,rangeL,rangeR)
        return 
    array0 =np.zeros(sampleCnt*2, np.float32)
    for i in range(sampleCnt):
        array0[i*2] = (2.0*i-sampleCnt)/sampleCnt  # x
        array0[i*2+1] = amplitude * math.sin(factor*(rangeL+i*range0/sampleCnt)) # y
    return array0


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

        # load shaders
        self.program = glutils.loadShaders(strVS, strFS)
        glUseProgram(self.program)             
        # set up VBOs
        vertexData = createSinArray(200, 1.0,1.0,-3*PI,3 * PI)
        self.vertexBuffer = glGenBuffers(1)
        glBindBuffer(GL_ARRAY_BUFFER, self.vertexBuffer)
        glBufferData(GL_ARRAY_BUFFER, 4*len(vertexData), vertexData, GL_STATIC_DRAW)
        # set up vertex array object (VAO)
        self.vao = glGenVertexArrays(1)
        glBindVertexArray(self.vao)
        glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 0, None)
        glEnableVertexAttribArray(0)
        # unbind VAO
        glBindVertexArray(0)
        glBindBuffer(GL_ARRAY_BUFFER, 0)    

    def render(self):       
        # use shader
        glUseProgram(self.program)
        # bind VAO
        glBindVertexArray(self.vao)
        # draw
        glDrawArrays(GL_LINE_STRIP, 0, 200)
        # 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(300, 300, "draw Sine Curve0 ", 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)
    PI = 3.14159265358979323846264
    # Loop until the user closes the window
    firstSinCurve0 = FirstSinCurve(1.0)        
    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)
 
        firstSinCurve0.render()                 
        # Swap front and back buffers
        glfw.swap_buffers(window)       
        # Poll for and process events
        glfw.poll_events()

    glfw.terminate()


            
          

六、參考文獻

1、他山隨悟博客https://blog.csdn.net/t3swing/article/details/78471135