Qt & OpenGLWindow - flicker on resizing - c++

Question

It appears if I drag-resize fast enough, the window itself is created by subclassing qwindow and making an openGLcontext on it
Code:
#include <QGuiApplication>
#include <QOpenGLContext>
#include <QWindow>
#include <QOpenGLFunctions_3_3_Core>
#include <stdio.h>
class OpenGLWindow : public QWindow, protected QOpenGLFunctions_3_3_Core{
public:
explicit OpenGLWindow();
~OpenGLWindow();
virtual void render();
bool isWindowInitialized;
void exposeEvent(QExposeEvent *event);
bool event(QEvent *event);
private:
QOpenGLContext* ctx;
QSurfaceFormat* fmt;
bool isGLInitialized;
GLuint VertexArrayID;
GLuint buffer1;
GLuint ProgramID;
};
bool OpenGLWindow::event(QEvent *event)
{
switch (event->type()) {
case QEvent::UpdateRequest:
render();
return true;
case QEvent::Close:
glDisableVertexAttribArray(0);
glDeleteBuffers(1, &buffer1);
glDeleteVertexArrays(1, &VertexArrayID);
glDeleteProgram(ProgramID);
return QWindow::event(event);
case QEvent::Resize:
if(isWindowInitialized && isGLInitialized)glViewport(0,0,width(),height());
return QWindow::event(event);
default:
return QWindow::event(event);
}
}
void OpenGLWindow::exposeEvent(QExposeEvent *event)
{
Q_UNUSED(event);
if (isExposed())render();
}
OpenGLWindow::OpenGLWindow()
:ctx(new QOpenGLContext)
,fmt(new QSurfaceFormat)
,isGLInitialized(0)
{
setSurfaceType(OpenGLSurface);
fmt->setRenderableType(QSurfaceFormat::OpenGL);
fmt->setVersion(3,3);
resize(640,480);
fmt->setProfile(QSurfaceFormat::CoreProfile);
setFormat(*fmt);
ctx->setFormat(*fmt);
ctx->create();
}
OpenGLWindow::~OpenGLWindow()
{}
void OpenGLWindow::render(){
//if(Image::isWindowInitialized || isExposed())return;
if(!isGLInitialized){
ctx->makeCurrent(this);
initializeOpenGLFunctions();
GLuint vsID = glCreateShader(GL_VERTEX_SHADER);
GLuint fsID = glCreateShader(GL_FRAGMENT_SHADER);
const char* vs="#version 330 core\n layout(location = 0) in vec3 vertexPosition_modelspace; \n void main(){ gl_Position.xyz = vertexPosition_modelspace; gl_Position.w = 1.0;}";
const char* fs="#version 330 core\n out vec4 color;\n void main(){ color = vec4(1,0,0,1);}";
glShaderSource(vsID, 1, &vs , NULL);
glCompileShader(vsID);
GLint isCompiled = 0;
glGetShaderiv(vsID, GL_COMPILE_STATUS, &isCompiled);
if(isCompiled == GL_FALSE){
GLint maxLength = 0;
glGetShaderiv(vsID, GL_INFO_LOG_LENGTH, &maxLength);
char info[512];
glGetShaderInfoLog(vsID, maxLength, &maxLength, info);
printf("%s",info);}
glShaderSource(fsID, 1, &fs , NULL);
glCompileShader(fsID);
glGetShaderiv(fsID, GL_COMPILE_STATUS, &isCompiled);
if(isCompiled == GL_FALSE){
GLint maxLength = 0;
glGetShaderiv(fsID, GL_INFO_LOG_LENGTH, &maxLength);
char info[512];
glGetShaderInfoLog(fsID, maxLength, &maxLength, info);
printf("%s",info);
}
GLuint ProgramID = glCreateProgram();
glAttachShader(ProgramID, vsID);
glAttachShader(ProgramID, fsID);
glLinkProgram(ProgramID);
glDeleteShader(vsID);
glDeleteShader(fsID);
static const GLfloat data1[] = { -1.0f, -1.0f, 0.0f, 1.0f, -1.0f, 0.0f, 0.0f, 1.0f, 0.0f };
glGenVertexArrays(1, &VertexArrayID);
glBindVertexArray(VertexArrayID);
glGenBuffers(1, &buffer1);
glBindBuffer(GL_ARRAY_BUFFER,buffer1);
glBufferData(GL_ARRAY_BUFFER, sizeof(data1),data1, GL_STATIC_DRAW);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0 ,3 ,GL_FLOAT ,GL_FALSE,0 ,(void*)0 );
glClearColor(1.0f, 0.0f, 0.4f,1.0f);
glUseProgram(ProgramID);
glViewport(0,0,width(),height());
isGLInitialized=true;
}
if(isExposed()){
glClear( GL_COLOR_BUFFER_BIT );
glDrawArrays(GL_TRIANGLES, 0, 3);
ctx->swapBuffers(this);
}
}
int main(int argc, char **argv)
{
QGuiApplication app(argc, argv);
OpenGLWindow* win = new OpenGLWindow();
win->show();
win->isWindowInitialized=true;
return app.exec();
}
I'm using Qt 5.4.2 on Qt Creator 3.4.1
Kit : Desktop Qt 5.4.2 MSVC2013 64bit
I'm kida lost here since i've never used openGL in qt and it's hard for me to picture where the problem might originate

Answer 1

Try setting a combination of any of the following attributes:
this->setAttribute(Qt::WA_OpaquePaintEvent, true);
this->setAttribute(Qt::WA_PaintOnScreen, true);
this->setAttribute(Qt::WA_DontCreateNativeAncestors, true);
this->setAttribute(Qt::WA_NativeWindow, true);
this->setAttribute(Qt::WA_NoSystemBackground, true);
this->setAttribute(Qt::WA_MSWindowsUseDirect3D, true);
this->setAutoFillBackground(false);