OpenGL ES2学习笔记（6）-- Line Strip和Line Loop

Line Strip

上一篇文章画了两条线段，但是用了4个点。如果几条线段首尾相接的话，可以让OpenGL把他们当成Line Strip来画，这样就可以用n+1个点来画n条线段。

代码

import java.nio.ByteBuffer
import java.nio.ByteOrder
import javax.media.opengl.GL

def vertexShaderCode = """
  attribute vec4 a_Position;

  void main() {                              
    gl_Position = a_Position;
    gl_PointSize = 10.0;
  }
"""

def fragmentShaderCode = """
  precision mediump float; 

  void main() {
    gl_FragColor = vec4(1.0,0.5,0.0,1.0);
  }
"""

def shaderProgram = glob.compileAndLink(vertexShaderCode,fragmentShaderCode)
def aPositionLocation = gl.glGetAttribLocation(shaderProgram.objectId,"a_Position")
shaderProgram.use()


def BYTES_PER_FLOAT = 4
def POSITION_ELEMENT_COUNT = 2
def POINT_COUNT = 4

def vertices = [
 -0.2f,-0.8f,-0.2f,0.0f,0.2f,-0.6f,] as float[]

def vertexData = ByteBuffer
        .allocateDirect(vertices.length * BYTES_PER_FLOAT)
        .order(ByteOrder.nativeOrder())
        .asFloatBuffer()
vertexData.put(vertices)
vertexData.position(0)
gl.glVertexAttribPointer(aPositionLocation,?   POSITION_ELEMENT_COUNT,gl.GL_FLOAT,false,vertexData)
gl.glEnableVertexAttribArray(aPositionLocation)


gl.glClearColor(0.0f,0.0f)
gl.glClear(gl.GL_COLOR_BUFFER_BIT)
gl.glLineWidth(4)
gl.glDrawArrays(gl.GL_LINE_STRIP,POINT_COUNT)

gl.glDrawArrays(gl.GL_LINE_STRIP,POINT_COUNT)

效果

Line Loop

如果Line Strip闭合的话，那么就变成了Line Loop。修改上面的脚本，把传递给glDrawArrays()方法的GL_LINE_STRIP参数改成GL_LINE_LOOP：

gl.glDrawArrays(gl.GL_LINE_LOOP,POINT_COUNT)