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Simple example of OpenGL 4.1 in a QGLWidget
/*
* GLWidgetOpenGL4Example.h
*
* Created on: Apr 23, 2016
* Author: roy_shilkrot
*
*/
class GLWidgetOpenGL4Example : public QGLWidget {
public:
GLWidgetOpenGL4Example(const QGLFormat& fmt):QGLWidget(fmt),vaoId(0),elementBuffer(0) {}
protected:
virtual void paintGL();
virtual void initializeGL();
virtual void resizeGL(int width, int height) { glViewport(0, 0, width, height); }
private:
const int vertexLocationInShader = 0;
GLuint vaoId;
GLuint elementBuffer;
QGLShaderProgram shaderProgram;
};
void GLWidgetOpenGL4Example::paintGL() {
glBindVertexArray(vaoId);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, elementBuffer);
shaderProgram.bind();
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
shaderProgram.release();
glBindVertexArray(0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
}
void GLWidgetOpenGL4Example::initializeGL() {
qInfo() << "Widget OpenGl: " << format().majorVersion() << "." << format().minorVersion();
qInfo() << "Context valid: " << context()->isValid();
qInfo() << "Really used OpenGl: " << context()->format().majorVersion() << "." << context()->format().minorVersion();
qInfo() << "OpenGl information: VENDOR: " << (const char*)glGetString(GL_VENDOR);
qInfo() << " RENDERDER: " << (const char*)glGetString(GL_RENDERER);
qInfo() << " VERSION: " << (const char*)glGetString(GL_VERSION);
qInfo() << " GLSL VERSION: " << (const char*)glGetString(GL_SHADING_LANGUAGE_VERSION);
glClearColor(0.0, 1.0, 0.0, 1.0);
//Faces:
vector<GLuint> f = {
0, 1, 2,
0, 2, 3
};
//Vertices:
vector<GLfloat> v = {
0.1, 0.1, 0.0, // 0
0.1, 0.9, 0.0, // 1
0.9, 0.9, 0.0, // 2
0.9, 0.1, 0.0 // 3
};
qInfo() << "VAO: generate Vertex Array";
glGenVertexArrays(1,&vaoId);
glBindVertexArray(vaoId);
{
// buffer for faces
glGenBuffers(1, &elementBuffer);
qInfo("VAO %d: new elements (faces) buffer %d: %d faces", vaoId, elementBuffer, f.size()/3);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, elementBuffer);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(GLuint) * f.size(), &(f[0]), GL_STATIC_DRAW);
}
// buffer for vertex positions
{
GLuint buffer;
glGenBuffers(1, &buffer);
qInfo("VAO %d: new position / vertex buffer %d: %d vertices", vaoId, buffer, v.size()/3);
glBindBuffer(GL_ARRAY_BUFFER, buffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat) * 3 * v.size(), &(v[0]), GL_STATIC_DRAW);
glVertexAttribPointer(vertexLocationInShader, 3, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(vertexLocationInShader);
}
glBindVertexArray(0);
const char *vsrc =
"uniform mat4 projectionMatrix; \n"
"uniform mat4 modelviewMatrix; \n"
" \n"
"layout(location = 0) in vec3 inPosition; \n"
"void main(void) \n"
"{ \n"
" gl_Position = projectionMatrix * \n"
" modelviewMatrix * \n"
" inPosition; \n"
"} \n";
const char *fsrc =
"layout(location = 0, index = 0) out vec4 fragColor; \n"
"void main(void) \n"
"{ \n"
" gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0); \n"
"} \n";
shaderProgram.addShaderFromSourceCode(QGLShader::Vertex, vsrc);
shaderProgram.addShaderFromSourceFile(QGLShader::Fragment, fsrc);
shaderProgram.bindAttributeLocation("inPosition", vertexLocationInShader);
shaderProgram.link();
//setup ortho projection
shaderProgram.bind();
QMatrix4x4 m;
shaderProgram.setUniformValue("modelviewMatrix", m);
m.ortho(0, 1, 0, 1, 0, -1);
shaderProgram.setUniformValue("projectionMatrix", m);
shaderProgram.release();
}
int main(int argc, char** argv) {
// Read command lines arguments.
QApplication application(argc, argv);
//Important: Setup the Core profile (and not the compatability profile, OpenGL 2.1)
QGLFormat fmt = QGLFormat::defaultFormat();
fmt.setVersion(4, 1);
fmt.setProfile(QGLFormat::CoreProfile);
// Instantiate the viewer.
GLWidgetOpenGL4Example glwidgetExample(fmt);
glwidgetExample.setWindowTitle("QGLWidget OpenGL 4 Example");
// Make the viewer window visible on screen.
glwidgetExample.show();
// Run main loop.
return application.exec();
}
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