Need help in optimizing a drawing code ...

[ahmadka]

Well I'm painting directly on 'image' (which is a QImage object) using QPainter painter(&image) ... and then use update and everything ..

The connectingPointsCalculator function gives me all the points between to coordinates .. about each of these the slanted lines are calculated .. I've checked the working for this function too, to see if it gives wrong results in horizontal cases or something .. but this is fine too .. Also, since the problem only exists when running the code on N900, it leads me to believe that maybe the updating/repainting procedure is different for the N900 than for PC ... Would double buffering help here ?

[wysota]

Well I'm painting directly on 'image' (which is a QImage object) using QPainter painter(&image) ... and then use update and everything ..

What is the base class of your widget? How is "image" related to the widget?

Would double buffering help here ?

Qt widgets are double buffered by default. Save the image to disk and open it in an external viewer, check if the image is correct or not. At worst update the whole widget each time.

[ahmadka]

Alright here's the breakdown of my program ... There's a Main Window, which is just a main window .. Then there's another class I made called Canvas .. an object of Canvas is stored in Main Window and is initialized from Main Window's contructor .. Canvas is my main class where all the paint events and mouse events are handled .. 'image' is just a QImage object contained within the Canvas class .. Drawing is done on this image ..

Here's a gist of my code ... Thought, only stuff relevant to this issue is presented here:

Here's Canvas.h: (was previously called 'Board' .. by Canvas I mean the widget which contains the image on which drawing is done)

class Canvas : public QWidget
{
    Q_OBJECT
 
public:
    Canvas(QWidget *parent = 0);
 
protected:
    void mousePressEvent(QMouseEvent *event);
    void mouseMoveEvent(QMouseEvent *event);
    void mouseReleaseEvent(QMouseEvent *event);
    void mouseDoubleClickEvent(QMouseEvent *);
    void paintEvent(QPaintEvent *event);
 
private:
    void drawLineTo(const QPoint &endPoint);
 
    QImage image; [B]//this is the image on which drawing is done[/B]
    QPoint lastPoint;
    QVector<QPoint> qPoints;
    //MainWindow *mainWindow;
    int minX;
    int minY;
    int maxX;
    int maxY;
    void connectingPointsCalculator3( QVector<QPoint>& inputqPoints, int x0, int y0, int x1, int y1);
};

class Canvas : public QWidget
{
    Q_OBJECT

public:
    Canvas(QWidget *parent = 0);

protected:
    void mousePressEvent(QMouseEvent *event);
    void mouseMoveEvent(QMouseEvent *event);
    void mouseReleaseEvent(QMouseEvent *event);
    void mouseDoubleClickEvent(QMouseEvent *);
    void paintEvent(QPaintEvent *event);

private:
    void drawLineTo(const QPoint &endPoint);

    QImage image; [B]//this is the image on which drawing is done[/B]
    QPoint lastPoint;
    QVector<QPoint> qPoints;
    //MainWindow *mainWindow;
    int minX;
    int minY;
    int maxX;
    int maxY;
    void connectingPointsCalculator3( QVector<QPoint>& inputqPoints, int x0, int y0, int x1, int y1);
};

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ConnectingPointsCalculator3 function .. (used to output a QVector of all the points which need to be connected to make all those lines to give the slanted effect ... only the point coordinates are calculated in this function):

void Canvas::connectingPointsCalculator3( QVector<QPoint>& inputqPoints, int x0, int y0, int x1, int y1)
{
    inputqPoints.clear();
    bool steep;
 
 
    int i=2;
 
    if( qAbs(y1-y0)>qAbs(x1-x0))
    {
        steep = true;
    }
    if(steep==true)
    {
        swap(x0,y0);
        swap(x1,y1);
    }
    if(x0>x1)
    {
        swap(x0,x1);
        swap(y0,y1);
    }
    int deltax = x1-x0;
    int deltay = qAbs(y1-y0);
    int error = deltax/2;
    int ystep=0;
    int y=y0;
    if(y0<y1)
    {
        ystep=1;
    }
    else
    {
        ystep=-1;
    }
    inputqPoints.resize(1);
    if(steep==true)
    {
        inputqPoints.insert(0,QPoint(y0-5,x0-5));
        inputqPoints.insert(1,QPoint(y0+5,x0+5));
    }
    else
    {
        inputqPoints.insert(0,QPoint(x0-5,y0-5));
        inputqPoints.insert(1,QPoint(x0+5,y0+5));
    }
    bool switchedLanes = false;
    int x= x0;
    while(x<(x1+1))
    {
        if(switchedLanes==false)
        {
            error = error - deltay;
            if(error<0)
            {
                y=y+ystep;
                error = error + deltax;
                switchedLanes = true;
            }
        }
        else
        {
            switchedLanes=false;
        }
 
 
        if(steep==true)
        {
            inputqPoints.insert(i,QPoint(y-5,x-5));
            inputqPoints.insert(i+1,QPoint(y+5,x+5));
            if((y-5)<minX)
            {
                minX=y-5;
            }
            if((x-5)<minY)
            {
                minY=x-5;
            }
            if((y+5)>maxX)
            {
                maxX=y+5;
            }
            if((x+5)>maxY)
            {
                maxY=x+5;
            }
        }
        else
        {
            inputqPoints.insert(i,QPoint(x-5,y-5));
            inputqPoints.insert(i+1,QPoint(x+5,y+5));
            if((x-5)<minX)
            {
                minX=x-5;
            }
            if((y-5)<minY)
            {
                minY=y-5;
            }
            if((x+5)>maxX)
            {
                maxX=x+5;
            }
            if((y+5)>maxY)
            {
                maxY=y+5;
            }
        }
        if(switchedLanes==false)
        {
            x++;
 
        }
        i++;
        i++;
 
    }
 
}

void Canvas::connectingPointsCalculator3( QVector<QPoint>& inputqPoints, int x0, int y0, int x1, int y1)
{
    inputqPoints.clear();
    bool steep;


    int i=2;

    if( qAbs(y1-y0)>qAbs(x1-x0))
    {
        steep = true;
    }
    if(steep==true)
    {
        swap(x0,y0);
        swap(x1,y1);
    }
    if(x0>x1)
    {
        swap(x0,x1);
        swap(y0,y1);
    }
    int deltax = x1-x0;
    int deltay = qAbs(y1-y0);
    int error = deltax/2;
    int ystep=0;
    int y=y0;
    if(y0<y1)
    {
        ystep=1;
    }
    else
    {
        ystep=-1;
    }
    inputqPoints.resize(1);
    if(steep==true)
    {
        inputqPoints.insert(0,QPoint(y0-5,x0-5));
        inputqPoints.insert(1,QPoint(y0+5,x0+5));
    }
    else
    {
        inputqPoints.insert(0,QPoint(x0-5,y0-5));
        inputqPoints.insert(1,QPoint(x0+5,y0+5));
    }
    bool switchedLanes = false;
    int x= x0;
    while(x<(x1+1))
    {
        if(switchedLanes==false)
        {
            error = error - deltay;
            if(error<0)
            {
                y=y+ystep;
                error = error + deltax;
                switchedLanes = true;
            }
        }
        else
        {
            switchedLanes=false;
        }


        if(steep==true)
        {
            inputqPoints.insert(i,QPoint(y-5,x-5));
            inputqPoints.insert(i+1,QPoint(y+5,x+5));
            if((y-5)<minX)
            {
                minX=y-5;
            }
            if((x-5)<minY)
            {
                minY=x-5;
            }
            if((y+5)>maxX)
            {
                maxX=y+5;
            }
            if((x+5)>maxY)
            {
                maxY=x+5;
            }
        }
        else
        {
            inputqPoints.insert(i,QPoint(x-5,y-5));
            inputqPoints.insert(i+1,QPoint(x+5,y+5));
            if((x-5)<minX)
            {
                minX=x-5;
            }
            if((y-5)<minY)
            {
                minY=y-5;
            }
            if((x+5)>maxX)
            {
                maxX=x+5;
            }
            if((y+5)>maxY)
            {
                maxY=y+5;
            }
        }
        if(switchedLanes==false)
        {
            x++;

        }
        i++;
        i++;

    }

}

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Function used to actually do all the drawing on the QImage object named 'image':

void Canvas::drawLineTo(const QPoint &endPoint)
{
    QPainter painter(&image);
 
    painter.setPen(QPen(Qt::black,1,Qt::SolidLine,Qt::RoundCap,Qt::RoundJoin));
    qPoints.clear();
    minX =999999;
    minY =999999;
    maxX =-999999;
    maxY =-999999;
    painter.setPen(Qt::blue);
    painter.drawEllipse(lastPoint,8,8);
    painter.setPen(Qt::red);
    painter.drawEllipse(endPoint,4,4);
    connectingPointsCalculator3(qPoints,lastPoint.x(),lastPoint.y(),endPoint.x(),endPoint.y());
    painter.setPen(Qt::black);
    painter.drawLines(qPoints);
 
    update (QRect(QPoint(minX,minY), QPoint(maxX,maxY)).normalized());
    //update();
    modified = true;
    lastPoint = endPoint;
}

void Canvas::drawLineTo(const QPoint &endPoint)
{
    QPainter painter(&image);

    painter.setPen(QPen(Qt::black,1,Qt::SolidLine,Qt::RoundCap,Qt::RoundJoin));
    qPoints.clear();
    minX =999999;
    minY =999999;
    maxX =-999999;
    maxY =-999999;
    painter.setPen(Qt::blue);
    painter.drawEllipse(lastPoint,8,8);
    painter.setPen(Qt::red);
    painter.drawEllipse(endPoint,4,4);
    connectingPointsCalculator3(qPoints,lastPoint.x(),lastPoint.y(),endPoint.x(),endPoint.y());
    painter.setPen(Qt::black);
    painter.drawLines(qPoints);

    update (QRect(QPoint(minX,minY), QPoint(maxX,maxY)).normalized());
    //update();
    modified = true;
    lastPoint = endPoint;
}

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3 functions to do the initialization within the Canvas object:

Canvas::Canvas(QWidget *parent)
{
    setAttribute(Qt::WA_StaticContents);
    reset();
    qPoints.clear();
}
 
void Canvas::reset()
{
    resizeImage(&image,QSize(800,400));
    image.fill(qRgb(255, 255, 255));
    update();
}
 
void Canvas::resizeImage(QImage *image, const QSize &newSize)
{
    if (image->size() == newSize)
        return;
 
    QImage newImage(newSize, QImage::Format_RGB32);
    QPainter painter(&newImage);
    painter.drawImage(QPoint(0, 0), *image);
    *image = newImage;
}

Canvas::Canvas(QWidget *parent)
{
    setAttribute(Qt::WA_StaticContents);
    reset();
    qPoints.clear();
}

void Canvas::reset()
{
    resizeImage(&image,QSize(800,400));
    image.fill(qRgb(255, 255, 255));
    update();
}

void Canvas::resizeImage(QImage *image, const QSize &newSize)
{
    if (image->size() == newSize)
        return;

    QImage newImage(newSize, QImage::Format_RGB32);
    QPainter painter(&newImage);
    painter.drawImage(QPoint(0, 0), *image);
    *image = newImage;
}

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Drawing event functions:

void Canvas::mousePressEvent(QMouseEvent *event)
{
    if(event->button() & Qt::LeftButton)
    {
        scribbling=true;
        lastPoint=event->pos();
    }
}
 
void Canvas::mouseMoveEvent(QMouseEvent *event)
{
    if((event->buttons() & Qt::LeftButton) && scribbling==true)
    {
        drawLineTo(event->pos());
    }
}
 
void Canvas::mouseReleaseEvent(QMouseEvent *event)
{
    if((event->button()&Qt::LeftButton)&&scribbling==true)
    {
        drawLineTo(event->pos());
        scribbling=false;
    }
}

void Canvas::mousePressEvent(QMouseEvent *event)
{
    if(event->button() & Qt::LeftButton)
    {
        scribbling=true;
        lastPoint=event->pos();
    }
}

void Canvas::mouseMoveEvent(QMouseEvent *event)
{
    if((event->buttons() & Qt::LeftButton) && scribbling==true)
    {
        drawLineTo(event->pos());
    }
}

void Canvas::mouseReleaseEvent(QMouseEvent *event)
{
    if((event->button()&Qt::LeftButton)&&scribbling==true)
    {
        drawLineTo(event->pos());
        scribbling=false;
    }
}

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Canvas paintEvent():

void Canvas::paintEvent(QPaintEvent *event)
{
    QPainter painter(this);
    QRect dirtyRect = event->rect();
    painter.drawImage(dirtyRect, image, dirtyRect);
}

void Canvas::paintEvent(QPaintEvent *event)
{
    QPainter painter(this);
    QRect dirtyRect = event->rect();
    painter.drawImage(dirtyRect, image, dirtyRect);
}

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if you need code for my Main Window as well, please let me know ... And please help me figure this silly bug out :P

[wysota]

So you are implementing the paintEvent after all

Please do the tests I asked you to do in the previous post.

[ahmadka]

Alright I was busy for the past couple of days so I couldn't work on this problem before .. Anyways I implemented an image save feature, and have saved a PNG file directly from the N900 .. Bad news, the image is exactly like I see it on the N900: Broken horizontal lines ..

Anyways, here's one picture saved through my program running on the N900 (the blue and red circles indicate the points between slanted lines need to be drawn):

[squidge]

Firstly, forget drawing for a bit. Look the positions you are trying to draw, and then load them in afterwards and draw them. This will tell you what the problem is.

Secondly, as Wysota says, please don't use imageshack (or any other third party image hosting site).

[ahmadka]

Okay yeh, I figured out the problem .. problem was in my connecting points code .. fixed it now, and now there are no breaks ..

Thanks for your help mate, and i apologize for uploading to imageshack .. forgot :P