QPainter doesn't seem to draw QImage

[Denarius]

Hello,
I want to draw a QImage based off of a PNG file.
It compiles fine, but it doesn't show my PNG file.

Here's the piece of code I use:

The .h

#ifndef DRAWINGMAP_H
#define DRAWINGMAP_H
 
#include <QtGui/QWidget>
#include "ui_drawingmap.h"
#include <QtCore/QList>
#include <QtGui/QImage>
 
struct myPos2D
{
	int x;
	int y;
	int yaw;
};
 
class DrawingMap : public QWidget
{
    Q_OBJECT
 
public:
    DrawingMap(QWidget *parent = 0);
    ~DrawingMap();
 
public slots:
	void setPos(int x , int y , int yaw);
	void setRobotDiameter(int diameter);
 
protected:
    void paintEvent(QPaintEvent *event);
 
 
private:
    Ui::DrawingMapClass ui;
 
    int x_pos, y_pos, yaw;
    int robotDiameter;
    int zoom;
 
    QImage robotImage;
 
    QList<myPos2D> positionList;
 
};
 
#endif // DRAWINGMAP_H

#ifndef DRAWINGMAP_H
#define DRAWINGMAP_H

#include <QtGui/QWidget>
#include "ui_drawingmap.h"
#include <QtCore/QList>
#include <QtGui/QImage>

struct myPos2D
{
	int x;
	int y;
	int yaw;
};

class DrawingMap : public QWidget
{
    Q_OBJECT

public:
    DrawingMap(QWidget *parent = 0);
    ~DrawingMap();

public slots:
	void setPos(int x , int y , int yaw);
	void setRobotDiameter(int diameter);

protected:
    void paintEvent(QPaintEvent *event);


private:
    Ui::DrawingMapClass ui;

    int x_pos, y_pos, yaw;
    int robotDiameter;
    int zoom;

    QImage robotImage;

    QList<myPos2D> positionList;

};

#endif // DRAWINGMAP_H

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The .cpp

#include "drawingmap.h"
 
#include <QtGui/QPainter>
 
DrawingMap::DrawingMap(QWidget *parent)
    : QWidget(parent)
{
	x_pos = y_pos = yaw = 0;
	robotDiameter = 10;
	zoom = 1;
 
	ui.setupUi(this);
}
 
DrawingMap::~DrawingMap()
{
 
}
 
void DrawingMap::paintEvent(QPaintEvent * /* event */)
 {
myPos2D newPos; //this is a struct with int x, int y, int yaw
 
     newPos.x = x_pos;
     newPos.y = y_pos;
     newPos.yaw = yaw;
 
     int oldX = 0, oldY = 0;
 
     positionList.append(newPos); //This is a QList
 
	 QPainter painter(this);
 
     painter.setPen(Qt::SolidLine);
     painter.setPen(Qt::red);
 
     painter.translate(rect().width()/2, rect().height()/2);
 
     //draw the robot trail
     for(int i = 0; i < positionList.size(); i++)
     {
    	 //draw trail
    	 painter.drawLine(oldX * zoom , oldY * zoom, positionList.at(i).x * zoom, positionList.at(i).y * zoom);
 
    	 //remember old positions
    	 oldX = positionList.at(i).x;
    	 oldY = positionList.at(i).y;
     }
 
     painter.setPen(Qt::NoPen);
     painter.setBrush(Qt::blue);
 
     //Get and correct image
     robotImage = QImage("myPNGfile.png"); //robotImage is a QImage
     robotImage.convertToFormat(QImage::Format_ARGB32_Premultiplied ,Qt::ColorOnly);
     //robotImage.createMaskFromColor(0x00000000,Qt::MaskOutColor); // make black transparent
 
     //Go to correct position
     painter.translate(x_pos * zoom, y_pos * zoom);
     painter.rotate(yaw);
     //draw the robot
     painter.drawImage(0 , 0 , robotImage);
 
/*
     painter.drawPie(QRect((-robotDiameter/2) * zoom, (-robotDiameter/2) * zoom, robotDiameter * zoom, robotDiameter * zoom), 0, 360 * 16);
     painter.setPen(Qt::SolidLine);
     painter.drawLine(0 , 0, 0 , (robotDiameter + robotDiameter/4) * zoom  );
	*/
}
 
void DrawingMap::setPos(int x , int y , int ya)
{
	x_pos = x;
	y_pos = y;
	yaw = ya;
 
	update();
}
 
void DrawingMap::setRobotDiameter(int diameter)
{
	zoom = diameter;
	update();
}

#include "drawingmap.h"

#include <QtGui/QPainter>

DrawingMap::DrawingMap(QWidget *parent)
    : QWidget(parent)
{
	x_pos = y_pos = yaw = 0;
	robotDiameter = 10;
	zoom = 1;

	ui.setupUi(this);
}

DrawingMap::~DrawingMap()
{

}

void DrawingMap::paintEvent(QPaintEvent * /* event */)
 {
myPos2D newPos; //this is a struct with int x, int y, int yaw

     newPos.x = x_pos;
     newPos.y = y_pos;
     newPos.yaw = yaw;

     int oldX = 0, oldY = 0;

     positionList.append(newPos); //This is a QList

	 QPainter painter(this);

     painter.setPen(Qt::SolidLine);
     painter.setPen(Qt::red);

     painter.translate(rect().width()/2, rect().height()/2);

     //draw the robot trail
     for(int i = 0; i < positionList.size(); i++)
     {
    	 //draw trail
    	 painter.drawLine(oldX * zoom , oldY * zoom, positionList.at(i).x * zoom, positionList.at(i).y * zoom);

    	 //remember old positions
    	 oldX = positionList.at(i).x;
    	 oldY = positionList.at(i).y;
     }

     painter.setPen(Qt::NoPen);
     painter.setBrush(Qt::blue);

     //Get and correct image
     robotImage = QImage("myPNGfile.png"); //robotImage is a QImage
     robotImage.convertToFormat(QImage::Format_ARGB32_Premultiplied ,Qt::ColorOnly);
     //robotImage.createMaskFromColor(0x00000000,Qt::MaskOutColor); // make black transparent

     //Go to correct position
     painter.translate(x_pos * zoom, y_pos * zoom);
     painter.rotate(yaw);
     //draw the robot
     painter.drawImage(0 , 0 , robotImage);

/*
     painter.drawPie(QRect((-robotDiameter/2) * zoom, (-robotDiameter/2) * zoom, robotDiameter * zoom, robotDiameter * zoom), 0, 360 * 16);
     painter.setPen(Qt::SolidLine);
     painter.drawLine(0 , 0, 0 , (robotDiameter + robotDiameter/4) * zoom  );
	*/
}

void DrawingMap::setPos(int x , int y , int ya)
{
	x_pos = x;
	y_pos = y;
	yaw = ya;

	update();
}

void DrawingMap::setRobotDiameter(int diameter)
{
	zoom = diameter;
	update();
}

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The .h from the .ui file Qt spit out

/********************************************************************************
** Form generated from reading ui file 'drawingmap.ui'
**
** Created: Mon Mar 2 11:22:28 2009
**      by: Qt User Interface Compiler version 4.4.3
**
** WARNING! All changes made in this file will be lost when recompiling ui file!
********************************************************************************/
 
#ifndef UI_DRAWINGMAP_H
#define UI_DRAWINGMAP_H
 
#include <QtCore/QVariant>
#include <QtGui/QAction>
#include <QtGui/QApplication>
#include <QtGui/QButtonGroup>
#include <QtGui/QWidget>
 
QT_BEGIN_NAMESPACE
 
class Ui_DrawingMapClass
{
public:
 
    void setupUi(QWidget *DrawingMapClass)
    {
    if (DrawingMapClass->objectName().isEmpty())
        DrawingMapClass->setObjectName(QString::fromUtf8("DrawingMapClass"));
    DrawingMapClass->resize(400, 300);
 
    retranslateUi(DrawingMapClass);
 
    QMetaObject::connectSlotsByName(DrawingMapClass);
    } // setupUi
 
    void retranslateUi(QWidget *DrawingMapClass)
    {
    DrawingMapClass->setWindowTitle(QApplication::translate("DrawingMapClass", "DrawingMap", 0, QApplication::UnicodeUTF8));
    Q_UNUSED(DrawingMapClass);
    } // retranslateUi
 
};
 
namespace Ui {
    class DrawingMapClass: public Ui_DrawingMapClass {};
} // namespace Ui
 
QT_END_NAMESPACE
 
#endif // UI_DRAWINGMAP_H

/********************************************************************************
** Form generated from reading ui file 'drawingmap.ui'
**
** Created: Mon Mar 2 11:22:28 2009
**      by: Qt User Interface Compiler version 4.4.3
**
** WARNING! All changes made in this file will be lost when recompiling ui file!
********************************************************************************/

#ifndef UI_DRAWINGMAP_H
#define UI_DRAWINGMAP_H

#include <QtCore/QVariant>
#include <QtGui/QAction>
#include <QtGui/QApplication>
#include <QtGui/QButtonGroup>
#include <QtGui/QWidget>

QT_BEGIN_NAMESPACE

class Ui_DrawingMapClass
{
public:

    void setupUi(QWidget *DrawingMapClass)
    {
    if (DrawingMapClass->objectName().isEmpty())
        DrawingMapClass->setObjectName(QString::fromUtf8("DrawingMapClass"));
    DrawingMapClass->resize(400, 300);

    retranslateUi(DrawingMapClass);

    QMetaObject::connectSlotsByName(DrawingMapClass);
    } // setupUi

    void retranslateUi(QWidget *DrawingMapClass)
    {
    DrawingMapClass->setWindowTitle(QApplication::translate("DrawingMapClass", "DrawingMap", 0, QApplication::UnicodeUTF8));
    Q_UNUSED(DrawingMapClass);
    } // retranslateUi

};

namespace Ui {
    class DrawingMapClass: public Ui_DrawingMapClass {};
} // namespace Ui

QT_END_NAMESPACE

#endif // UI_DRAWINGMAP_H

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The slots are used so that I can change the robot position and direction.
This QWidget is inserted in another QWidget which is the main window in my program.
I inserted my custom QWidget with Qt Designer and promoted the widget.
So it should be all standard Qt Designer code

It paints the Lines just fine.
And the very simple representation of the robot as well, that is the blue dot I commented out of the program.

[caduel]

have you checked that/if
a) the image is found (maybe its in a subdirectory or in a resource (":/...") )
b) your Qt supports png
c) the file is a png (not a gif just named png... happened to me once ;-)


side note: for performance reasons I would move the loading/converting of the image out of the paintEvent (maybe into the widget's constructor)

[Denarius]

have you checked that/if
a) the image is found (maybe its in a subdirectory or in a resource (":/...") )
b) your Qt supports png
c) the file is a png (not a gif just named png... happened to me once ;-)


side note: for performance reasons I would move the loading/converting of the image out of the paintEvent (maybe into the widget's constructor)

a) yes it's found. otherwise it would give me a compiler error stating that it didn't find the image.
b) How do you check this?
The Qt api states that it supports PNG files, so would this be the answer?
c) the file extension is .png So I'm pretty shure it's a png
I also tried the GIF extension etc. But no luck, same problem

i'll do the performance later. I just want the image to draw first.

[Denarius]

Ahw,
I found the problem.
i had to put a ./ before the whole path

[talk2amulya]

so caduel was right image file wasnt found..u r using a qrc file so it wont give a compilation error if the file isnt found..all will be done at compile time

[Denarius]

new problem.

I've changed the code for drawing the image file to this:

//Correct image
     robotImage.convertToFormat(QImage::Format_ARGB32_Premultiplied ,Qt::AutoColor);
     //robotImage.createMaskFromColor(0x00000000,Qt::MaskOutColor); // make black transparent
     robotImage.scaled(robotDiameter * zoom, robotDiameter * zoom , Qt::KeepAspectRatioByExpanding, Qt::SmoothTransformation);
     int offset_x = -robotImage.width() / 2;
	 int offset_y = -robotImage.height() / 2;
 
     //Go to correct position
     painter.translate(x_pos * zoom, y_pos * zoom);
     painter.rotate(yaw);
     //draw the robot
     painter.drawImage(offset_x , offset_y , robotImage, 0 , 0 , robotImage.width() * zoom , robotImage.height() * zoom);

//Correct image
     robotImage.convertToFormat(QImage::Format_ARGB32_Premultiplied ,Qt::AutoColor);
     //robotImage.createMaskFromColor(0x00000000,Qt::MaskOutColor); // make black transparent
     robotImage.scaled(robotDiameter * zoom, robotDiameter * zoom , Qt::KeepAspectRatioByExpanding, Qt::SmoothTransformation);
     int offset_x = -robotImage.width() / 2;
	 int offset_y = -robotImage.height() / 2;

     //Go to correct position
     painter.translate(x_pos * zoom, y_pos * zoom);
     painter.rotate(yaw);
     //draw the robot
     painter.drawImage(offset_x , offset_y , robotImage, 0 , 0 , robotImage.width() * zoom , robotImage.height() * zoom);

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But it doesn't resize or rescale the image.
Or am I missing something?

P.S.
I loaded the image in the constructor now. Thanks for the suggestion

[^NyAw^]

Hi,

You are scaling the image but you don't store the returning image of the method to any variable:

robotImage.scaled(robotDiameter * zoom, robotDiameter * zoom , Qt::KeepAspectRatioByExpanding, Qt::SmoothTransformation);

robotImage.scaled(robotDiameter * zoom, robotDiameter * zoom , Qt::KeepAspectRatioByExpanding, Qt::SmoothTransformation);

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to:

QImage qScaledImage = robotImage.scaled(robotDiameter * zoom, robotDiameter * zoom , Qt::KeepAspectRatioByExpanding, Qt::SmoothTransformation);

QImage qScaledImage = robotImage.scaled(robotDiameter * zoom, robotDiameter * zoom , Qt::KeepAspectRatioByExpanding, Qt::SmoothTransformation);

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Then you have to paint "qScaledImage"

[Denarius]

Hi,

You are scaling the image but you don't store the returning image of the method to any variable:

robotImage.scaled(robotDiameter * zoom, robotDiameter * zoom , Qt::KeepAspectRatioByExpanding, Qt::SmoothTransformation);

robotImage.scaled(robotDiameter * zoom, robotDiameter * zoom , Qt::KeepAspectRatioByExpanding, Qt::SmoothTransformation);

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to:

QImage qScaledImage = robotImage.scaled(robotDiameter * zoom, robotDiameter * zoom , Qt::KeepAspectRatioByExpanding, Qt::SmoothTransformation);

QImage qScaledImage = robotImage.scaled(robotDiameter * zoom, robotDiameter * zoom , Qt::KeepAspectRatioByExpanding, Qt::SmoothTransformation);

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Then you have to paint "qScaledImage"

This worked like a charm.
Thank you very much