Fail to generate a triangle by openGL with Qt5.0.2 - c++

Question

OS : mac osx 10.8.3
compiler : clang3.2
I am a beginner of opengl, trying to play opengl with Qt5
There are two problems about this simple program(plot a triangle)
I can't see the triangle
The program could not exit even I close the window
hpp
#include <QGLWidget>
#include <QtGui/QOpenGLFunctions>
#include <QtGui/QOpenGLShaderProgram>
class QWidget;
class ch1HelloTriangle : public QGLWidget, protected QOpenGLFunctions
{
Q_OBJECT
public:
explicit ch1HelloTriangle(QWidget *parent = 0);
protected:
virtual void initializeGL();
void initShaders();
void InitializeVertexBuffer();
virtual void resizeGL(int w, int h);
virtual void paintGL();
private:
QOpenGLShaderProgram program;
GLuint positionBufferObject;
};
.cpp
#include <locale.h>
#include <QWidget>
#include "ch1HelloTriangle.hpp"
namespace
{
float const vertexPositions[] = {
0.75f, 0.75f, 0.0f, 1.0f,
0.75f, -0.75f, 0.0f, 1.0f,
-0.75f, -0.75f, 0.0f, 1.0f,
};
}
ch1HelloTriangle::ch1HelloTriangle(QWidget *parent) :
QGLWidget(parent)
{
}
void ch1HelloTriangle::initializeGL()
{
initializeOpenGLFunctions();
InitializeVertexBuffer();
initShaders();
}
void ch1HelloTriangle::initShaders()
{
// Override system locale until shaders are compiled
setlocale(LC_NUMERIC, "C");
// Compile vertex shader
if (!program.addShaderFromSourceCode(QOpenGLShader::Vertex,
"attribute vec4 position;\n"
"void main()\n"
"{\n"
" gl_Position = position;\n"
"}\n"))
{
close();
}
// Compile fragment shader
if (!program.addShaderFromSourceCode(QOpenGLShader::Fragment,
"out vec4 outputColor;\n"
"void main()\n"
"{\n"
" outputColor = vec4(1.0f, 1.0f, 1.0f, 1.0f);\n"
"}\n"))
{
close();
}
// Link shader pipeline
if (!program.link())
close();
// Bind shader pipeline for use
if (!program.bind())
close();
// Restore system locale
setlocale(LC_ALL, "");
}
void ch1HelloTriangle::InitializeVertexBuffer()
{
glGenBuffers(1, &positionBufferObject);
glBindBuffer(GL_ARRAY_BUFFER, positionBufferObject);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertexPositions), vertexPositions, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);
}
void ch1HelloTriangle::resizeGL(int w, int h)
{
// Set OpenGL viewport to cover whole widget
glViewport(0, 0, w, h);
}
void ch1HelloTriangle::paintGL()
{
/*
//codes propose by http://stackoverflow.com/questions/13111291/displaying-a-triangle-with-qt-and-opengl?rq=1, can't see the triangle either
QSize viewport_size = size();
glViewport(0, 0, viewport_size.width(), viewport_size.height());
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glFrustum(-1, 1, -1, 1, 5, 7); // near and far match your triangle Z distance
glMatrixMode(GL_MODELVIEW);*/
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT);
glBindBuffer(GL_ARRAY_BUFFER, positionBufferObject);
int vertexLocation = program.attributeLocation("position");
program.enableAttributeArray(vertexLocation);
glVertexAttribPointer(vertexLocation, 4, GL_FLOAT, GL_FALSE, 0, 0);
glDrawArrays(GL_TRIANGLES, 0, 3);
}
main.cpp
#include <QApplication>
#include "ch1HelloTriangle.hpp"
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
ch1HelloTriangle ch1;
ch1.show();
return a.exec();
}

Answer 1

After a lot of trial and error, I solved the problem.
Change two things :
1 : read the shader by files
// Compile vertex shader
if (!program.addShaderFromSourceFile(QOpenGLShader::Vertex, "modernOpenGLShader/ch1/vertex")){
QMessageBox::warning(this, "QOpenGLShader::Vertex", "QOpenGLShader::Vertex" + program.log());
close();
}
// Compile fragment shader
if (!program.addShaderFromSourceFile(QOpenGLShader::Fragment, "modernOpenGLShader/ch1/frag")){
QMessageBox::warning(this, "QOpenGLShader::Fragment", "QOpenGLShader::Fragment" + program.log());
close();
}
2 : change the fragment shader, remove the output variable
void main() {
//set every drawn pixel to white
gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);
}
From the websites, "modern opengl":http://www.arcsynthesis.org/gltut/
and "another site":tomdalling.com/blog/modern-opengl/01-getting-started-in-xcode-and-visual-cpp/
The output qualify should exist(atleast the codes of the second website will work on my pc)
But Qt will throw error message
QOpenGLShader::FragmentERROR: 0:4: Invalid qualifiers 'out' in global variable context
Do anyone know why?Thanks