Qt 5.3.2 / OSX cannot use native CGContext drawing in paintEvent / Flickering

[nils_heidorn]

Hi !
For the life of me i cannot use native drawing in a paintEvent on Qt 5.

I created a simple example that should fill the whole Rectangle with a certain color (RGB 240,120,60).
When started (on Mac of course, i used 10.9) the WIndow flickers some times between white and the desired “orange” color and then stays white.
Do you have any idea why my drawing is not persistent ?
A very similar way of drawing in Qt4 is working just fine.

Here is my sample:

nativepainter.pro:

QT       += core gui macextras
 
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
 
TARGET = nativePainter
TEMPLATE = app
LIBS += -framework CoreGraphics
 
SOURCES += main.cpp\
 nativepainter.cpp
 
HEADERS  += \
 nativepainter.h

QT       += core gui macextras
 
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
 
TARGET = nativePainter
TEMPLATE = app
LIBS += -framework CoreGraphics
 
SOURCES += main.cpp\
 nativepainter.cpp
 
HEADERS  += \
 nativepainter.h

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main.cpp:

#include <QApplication>
#include <nativepainter.h>
 
int main(int argc, char *argv[])
{
 QApplication a(argc, argv);
 nativePainter myNP;
 myNP.show();
 
 return a.exec();
}

#include <QApplication>
#include <nativepainter.h>
 
int main(int argc, char *argv[])
{
 QApplication a(argc, argv);
 nativePainter myNP;
 myNP.show();
 
 return a.exec();
}

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nativepainter.h:

#ifndef NATIVEPAINTER_H
#define NATIVEPAINTER_H
 
#include <QApplication>
#include <QWidget>
#include <QPaintEvent>
#include <CoreGraphics/CGColorSpace.h>
#include <ApplicationServices/ApplicationServices.h>
 
class nativePainter : public QWidget
{
 Q_OBJECT
public:
 explicit nativePainter(QWidget *parent = 0);
signals:
 
public slots:
protected:
 void paintEvent(QPaintEvent * event);
private:
};
 
#endif // NATIVEPAINTER_H

#ifndef NATIVEPAINTER_H
#define NATIVEPAINTER_H
 
#include <QApplication>
#include <QWidget>
#include <QPaintEvent>
#include <CoreGraphics/CGColorSpace.h>
#include <ApplicationServices/ApplicationServices.h>
 
class nativePainter : public QWidget
{
 Q_OBJECT
public:
 explicit nativePainter(QWidget *parent = 0);
signals:
 
public slots:
protected:
 void paintEvent(QPaintEvent * event);
private:
};
 
#endif // NATIVEPAINTER_H

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nativepainter.cpp:

#include <Qpainter>
#include <QDebug>
#include "nativepainter.h"
#ifdef Q_OS_MACX
#include <QtMac>
#endif
 
nativePainter::nativePainter(QWidget *parent) :
 QWidget(parent)
{
 
}
 
void nativePainter::paintEvent(QPaintEvent* e)
{
#ifdef Q_OS_MACX
//prepare painting
 QPainter painter;
 painter.begin(this);
 painter.beginNativePainting();
 
//create pixelbuffer and fill with RGB color (240,120,60)
 int componentCount(4), w(e->rect().width()), h(e->rect().height());
 size_t bufferLength = w * h * componentCount*2;
 unsigned char* pixels = (unsigned char*)malloc(bufferLength);
 for(ulong i=0; i < bufferLength; i+=componentCount)
 {
  pixels[i] = 240;
  pixels[i+1] = 120;
  pixels[i+2] = 60;
  pixels[i+3] = 255;
 }
 CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, pixels, bufferLength, NULL);
 size_t bitsPerComponent = 8;
 size_t bitsPerPixel = bitsPerComponent * componentCount;
 size_t bytesPerRow = componentCount * w;
 CGColorSpaceRef RGBcolorSpaceRef = CGColorSpaceCreateDeviceRGB();
 CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault | kCGImageAlphaPremultipliedLast;
 CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
 
//create CGImageRef with pixels
 CGImageRef iref = CGImageCreate(
   w,
   h,
   bitsPerComponent,
   bitsPerPixel,
   bytesPerRow,
   RGBcolorSpaceRef,
   bitmapInfo,
   provider,   // data provider
   NULL,       // decode
   true,        // should interpolate
   renderingIntent);
 
//draw CGImage to current context
 CGRect cgrect = CGRectMake(e->rect().x(), e->rect().y(), e->rect().x() + e->rect().width(), e->rect().y() + e->rect().height());
 CGContextRef context = QtMac::currentCGContext();
 CGContextDrawImage(context, cgrect, iref);
 CGContextFlush(context);
 CGContextSynchronize(context);
//end painting
 painter.endNativePainting();
 painter.end();
#else
 QPainter painter;
 painter.begin(this);
 painter.fillRect(e->rect(), QColor(240, 120, 60));
 painter.end();
#endif
}

#include <Qpainter>
#include <QDebug>
#include "nativepainter.h"
#ifdef Q_OS_MACX
#include <QtMac>
#endif
 
nativePainter::nativePainter(QWidget *parent) :
 QWidget(parent)
{
 
}
 
void nativePainter::paintEvent(QPaintEvent* e)
{
#ifdef Q_OS_MACX
//prepare painting
 QPainter painter;
 painter.begin(this);
 painter.beginNativePainting();
 
//create pixelbuffer and fill with RGB color (240,120,60)
 int componentCount(4), w(e->rect().width()), h(e->rect().height());
 size_t bufferLength = w * h * componentCount*2;
 unsigned char* pixels = (unsigned char*)malloc(bufferLength);
 for(ulong i=0; i < bufferLength; i+=componentCount)
 {
  pixels[i] = 240;
  pixels[i+1] = 120;
  pixels[i+2] = 60;
  pixels[i+3] = 255;
 }
 CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, pixels, bufferLength, NULL);
 size_t bitsPerComponent = 8;
 size_t bitsPerPixel = bitsPerComponent * componentCount;
 size_t bytesPerRow = componentCount * w;
 CGColorSpaceRef RGBcolorSpaceRef = CGColorSpaceCreateDeviceRGB();
 CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault | kCGImageAlphaPremultipliedLast;
 CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
 
//create CGImageRef with pixels
 CGImageRef iref = CGImageCreate(
   w,
   h,
   bitsPerComponent,
   bitsPerPixel,
   bytesPerRow,
   RGBcolorSpaceRef,
   bitmapInfo,
   provider,   // data provider
   NULL,       // decode
   true,        // should interpolate
   renderingIntent);
 
//draw CGImage to current context
 CGRect cgrect = CGRectMake(e->rect().x(), e->rect().y(), e->rect().x() + e->rect().width(), e->rect().y() + e->rect().height());
 CGContextRef context = QtMac::currentCGContext();
 CGContextDrawImage(context, cgrect, iref);
 CGContextFlush(context);
 CGContextSynchronize(context);
//end painting
 painter.endNativePainting();
 painter.end();
#else
 QPainter painter;
 painter.begin(this);
 painter.fillRect(e->rect(), QColor(240, 120, 60));
 painter.end();
#endif
}

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May try to compile and see for yourself, do you guys have any idea ?

Greetings & Thanks,

Nils

[anda_skoa]

Maybe using widget attributes Qt::WA_OpaquePaintEvent or Qt::WA_NoSystemBackground could help?

Cheers,
_

[nils_heidorn]

Hello anda_skoa,
damn, that sounded just like it, BUT:
Using either of your proposed attributes or both ends up in the same kind of flickering only with black as the end state instead of "regular windows-backround-color". Same happened in one of my experiments before when i set the background color to transparent(via pallette entry):
Argh, i am frustrated :-(

Thanks though !

Nils