一、目的
1、正弦函数的基本画法；
2、GLSL方式实现练习。
二、程序运行结果
三、glDrawArrays 函数
GLSL画这些基本的类型使用的函数主要是glDraw*系列的函数：
void glDrawArrays (GLenum mode, GLint first, GLsizei count);
mode有以下类型，画点GL_POINTS，画线 GL_LINES，顺连线段GL_LINE_STRIP，回环线段GL_LINE_LOOP，三角形GL_TRIANGLES，GL_TRIANGLE_STRIP，GL_TRIANGLE_FAN，四边形GL_QUADS，GL_QUAD_STRIP，多边形GL_POLYGON。
first为0即可，
count表示要绘制顶点的个数。
四、正弦波绘制
正弦波公式是y = sin(x ) ，通过描点画出图形。需确定了以下几个参数来画正弦波：
1. sampleCnt：采样点个数，openGL画东西都采用逼近的方式，采样点越多，正弦波就越精细。
2. factor：用来控制正弦波的频率，如sin(2x ),sin(3x ) 等。
3. amplitude：振幅，用来控制正弦波的振幅，如3sin(2x )。
4. rangeL：我们要把正弦波映射到[-1.0,1.0]的范围内,否则画出来的正弦波都看不到。
5. rangeR：如传的-pi~pi的范围，会把这个范围的正弦波映射到[-1.0,1.0]范围内。
注意：shader里面y坐标统一乘了0.9，主要是避免图形顶到边框。
五、源代码
"""
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、参考文献
1、他山随悟博客https://blog.csdn.net/t3swing/article/details/78471135
