Qt opengl use shader to draw triangle

[zhangzhisheng]

I just want to draw a triangle with Qt. When I run the program, there is no triangle. What is wrong with my code?

#include "glwidget.h"

GLWidget::GLWidget(QWidget *parent) :QOpenGLWidget(parent)
{
this->setFocusPolicy(Qt::StrongFocus);
QSurfaceFormat format;
format.setDepthBufferSize(24);
format.setMajorVersion(4);
format.setMinorVersion(2);
format.setSamples(16);
format.setProfile(QSurfaceFormat::CoreProfile);
setFormat(format);
}

void GLWidget::initializeGL()
{
initializeOpenGLFunctions();
glClearColor(0.13F, 0.13F, 0.14F, 0.0F);
m_shaderProgram.addShaderFromSourceFile(QOpenGLShader::Vertex,"../PCRP/vertexshadercode.vert");
m_shaderProgram.addShaderFromSourceFile(QOpenGLShader::Fragment,"../PCRP/fragmentshadercode.frag");
m_shaderProgram.link();
m_MVPMatrixLoc=m_shaderProgram.uniformLocation("u_MVPMatrix");
GLfloat vertex[]={1.0,0.0,0.0,1.0,
0.0,1.0,0.0,1.0,
1.0,1.0,0.0,1.0};
m_Vbo.create();
m_Vbo.setUsagePattern(QOpenGLBuffer::StaticDraw);
m_Vbo.bind();
m_Vbo.allocate(vertex,sizeof(vertex));
m_ViewMatrix.lookAt(QVector3D(0.0f, 0.0f, 1.5f), QVector3D(0.0f, 0.0f, -5.0f), QVector3D(0.0f, 1.0f, 0.0f));
}

void GLWidget::paintGL()
{
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
glEnable(GL_DEPTH_TEST);
glEnable(GL_MULTISAMPLE);
m_shaderProgram.bind();
m_shaderProgram.enableAttributeArray("a_Position");
m_shaderProgram.setAttributeBuffer("a_Position",GL_FLOAT,0,4);

m_ModelMatrix.setToIdentity();
m_MVPMatrix=m_ProjectionMatrix*m_ViewMatrix*m_ModelMatrix;

m_shaderProgram.setUniformValue(m_MVPMatrixLoc,m_MVPMatrix);
glDrawArrays(GL_TRIANGLES,0,3);

}

void GLWidget::resizeGL(int w, int h)
{
glViewport(0, 0, (GLint)width(), (GLint)height());
m_ProjectionMatrix.setToIdentity();
m_ProjectionMatrix.perspective(45,(float) (width()/height()),0.1f,1000.0f);
}

this is vertexshadercode.vert

attribute vec4 a_Position;

uniform mat4 u_MVPMatrix;

void main()
{

gl_Position = u_MVPMatrix*a_Position;
} ;

this is fragmentshadercode.frag

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