编译链接着色器程序，进行绘制

三角形的绘制实现类。

//
// Created by ByteFlow on 2019/7/9.
//

#include "TriangleSample.h"
#include "../util/GLUtils.h"
#include "../util/LogUtil.h"

TriangleSample::TriangleSample()
{

}

TriangleSample::~TriangleSample()
{
if (m_ProgramObj)
{
glDeleteProgram(m_ProgramObj);
}

}

void TriangleSample::Init()
{
char vShaderStr[] =
"#version 300 es "
"layout(location = 0) in vec4 vPosition; "
"void main() "
"{ "
" gl_Position = vPosition; "
"} ";

char fShaderStr[] =
"#version 300 es "
"precision mediump float; "
"out vec4 fragColor; "
"void main() "
"{ "
" fragColor = vec4 ( 1.0, 0.0, 0.0, 1.0 ); "
"} ";

m_ProgramObj = GLUtils::CreateProgram(vShaderStr, fShaderStr, m_VertexShader, m_FragmentShader);

}

void TriangleSample::Draw()
{
LOGCATE("TriangleSample::Draw");
GLfloat vVertices[] = {
0.0f, 0.5f, 0.0f,
-0.5f, -0.5f, 0.0f,
0.5f, -0.5f, 0.0f,
};

if(m_ProgramObj == 0)
return;

// Use the program object
glUseProgram (m_ProgramObj);

// Load the vertex data
glVertexAttribPointer (0, 3, GL_FLOAT, GL_FALSE, 0, vVertices );
glEnableVertexAttribArray (0);

glDrawArrays (GL_TRIANGLES, 0, 3);

}

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编译和链接着色器程序的类

#include "GLUtils.h"
#include "LogUtil.h"
#include <stdlib.h>

GLuint GLUtils::LoadShader(GLenum shaderType, const char *pSource)
{
GLuint shader = 0;
shader = glCreateShader(shaderType);
if (shader)
{
glShaderSource(shader, 1, &pSource, NULL);
glCompileShader(shader);
GLint compiled = 0;
glGetShaderiv(shader, GL_COMPILE_STATUS, &compiled);
if (!compiled)
{
GLint infoLen = 0;
glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &infoLen);
if (infoLen)
{
char* buf = (char*) malloc((size_t)infoLen);
if (buf)
{
glGetShaderInfoLog(shader, infoLen, NULL, buf);
LOGCATE("GLUtils::LoadShader Could not compile shader %d: %s ", shaderType, buf);
free(buf);
}
glDeleteShader(shader);
shader = 0;
}
}
}
return shader;
}

GLuint GLUtils::CreateProgram(const char *pVertexShaderSource, const char *pFragShaderSource, GLuint &vertexShaderHandle, GLuint &fragShaderHandle)
{
GLuint program = 0;
vertexShaderHandle = LoadShader(GL_VERTEX_SHADER, pVertexShaderSource);
if (!vertexShaderHandle) return program;

fragShaderHandle = LoadShader(GL_FRAGMENT_SHADER, pFragShaderSource);
if (!fragShaderHandle) return program;

program = glCreateProgram();
if (program)
{
glAttachShader(program, vertexShaderHandle);
CheckGLError("glAttachShader");
glAttachShader(program, fragShaderHandle);
CheckGLError("glAttachShader");
glLinkProgram(program);
GLint linkStatus = GL_FALSE;
glGetProgramiv(program, GL_LINK_STATUS, &linkStatus);

glDetachShader(program, vertexShaderHandle);
glDeleteShader(vertexShaderHandle);
vertexShaderHandle = 0;
glDetachShader(program, fragShaderHandle);
glDeleteShader(fragShaderHandle);
fragShaderHandle = 0;
if (linkStatus != GL_TRUE)
{
GLint bufLength = 0;
glGetProgramiv(program, GL_INFO_LOG_LENGTH, &bufLength);
if (bufLength)
{
char* buf = (char*) malloc((size_t)bufLength);
if (buf)
{
glGetProgramInfoLog(program, bufLength, NULL, buf);
LOGCATE("GLUtils::CreateProgram Could not link program: %s ", buf);
free(buf);
}
}
glDeleteProgram(program);
program = 0;
}
}
LOGCATE("GLUtils::CreateProgram program = %d", program);
return program;
}

void GLUtils::DeleteProgram(GLuint &program)
{
LOGCATE("GLUtils::DeleteProgram");
if (program)
{
glUseProgram(0);
glDeleteProgram(program);
program = 0;
}
}

void GLUtils::CheckGLError(const char *pGLOperation)
{
for (GLint error = glGetError(); error; error = glGetError())
{
LOGCATE("GLUtils::CheckGLError GL Operation %s() glError (0x%x) ", pGLOperation, error);
}

}

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在 Init 函数中实现编译链接着色器程序 m_ProgramObj ，其中顶点着色器脚本：

#version 300 es
layout(location = 0) in vec4 vPosition;
void main()
{
gl_Position = vPosition;
}
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片元着色器脚本：

#version 300 es
precision mediump float;
out vec4 fragColor;
void main()
{
fragColor = vec4 ( 1.0, 0.0, 0.0, 1.0 ); //填充三角形区域为红色
}
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在 Draw 函数中指定着色器程序，为着色器程序中的变量赋值，传入顶点坐标信息，然后绘制三角形。

opengles 坐标系中三角形顶点坐标：