Query in 40000 chip demo

[aamer4yu]

I am new to Qt and was exploring demos of Qt.
I was trying the 40000 chip demo code and faced some confusion

1) I want to know the significance of choosing -11000 to 11000 in the function void MainWindow::populateScene()

2) if i change the loop, the chip movemment gets slow


The loop in void MainWindow::populateScene() function is

for (int i = -11000; i < 11000; i += 110) {
        ++xx;
        int yy = 0;
        for (int j = -7000; j < 7000; j += 70) {
            ++yy;
            qreal x = (i + 11000) / 22000.0;
            qreal y = (j + 7000) / 14000.0;
 
            QColor color(image.pixel(int(image.width() * x), int(image.height() * y)));
            QGraphicsItem *item = new Chip(color, xx, yy);
            item->setPos(QPointF(i, j));
            scene->addItem(item);
 
            ++nitems;
        }
    }

for (int i = -11000; i < 11000; i += 110) {
        ++xx;
        int yy = 0;
        for (int j = -7000; j < 7000; j += 70) {
            ++yy;
            qreal x = (i + 11000) / 22000.0;
            qreal y = (j + 7000) / 14000.0;

            QColor color(image.pixel(int(image.width() * x), int(image.height() * y)));
            QGraphicsItem *item = new Chip(color, xx, yy);
            item->setPos(QPointF(i, j));
            scene->addItem(item);
       
            ++nitems;
        }
    }

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If i replace the loop with

for (int i = 0; i < 22000; i += 110) {
        ++xx;
        int yy = 0;
        for (int j = 0; j < 14000; j += 70) {
            ++yy;
            qreal x = (i) / 22000.0;
            qreal y = (j) / 14000.0;
 
	int w,h;
	w= image.width();
	h= image.height();
            QColor color(image.pixel(int(image.width() * x), int(image.height() * y)));
            QGraphicsItem *item = new Chip(color, xx, yy);
            item->setPos(QPointF(i, j));
            scene->addItem(item);
 
 
	++nitems;
        }
    }

for (int i = 0; i < 22000; i += 110) {
        ++xx;
        int yy = 0;
        for (int j = 0; j < 14000; j += 70) {
            ++yy;
            qreal x = (i) / 22000.0;
            qreal y = (j) / 14000.0;

	int w,h;
	w= image.width();
	h= image.height();
            QColor color(image.pixel(int(image.width() * x), int(image.height() * y)));
            QGraphicsItem *item = new Chip(color, xx, yy);
            item->setPos(QPointF(i, j));
            scene->addItem(item);


	++nitems;
        }
    }

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and move the chips in the view, the movement is much slow.

What am i missing here ???

[aamer4yu]

None to solve the logical problem ????

[jacek]

2) if i change the loop, the chip movemment gets slow

Is it still slow after you restore the original version and recompile it? Maybe you have disabled the optimization or you do a debug build?

[wysota]

1) I want to know the significance of choosing -11000 to 11000 in the function void MainWindow:opulateScene()

The scene (0,0) coordinate is in the middle of the scene.

[aamer4yu]

@ Jacek
yes i tried rebuilding the application, using each loop

@wysota,
thx, even i guessed that it is in middle, in fact the aim of writing the new loop was to see how zoom would be affected if the middle is changed to top left

So I would like to know how changing the middle cordinate of the scenen si affecting the speed of dragging ??

Any help ?

[aamer4yu]

@jacek... sorry didnt annwer u completely..
well the original version runs fine when i restore to it.
And ia m not using any optimization,,,using the defaults when i open the project in Visual Studio.
The problem is occuring when i change the loop , making the middle cordinates as top left.

[wysota]

So I would like to know how changing the middle cordinate of the scenen si affecting the speed of dragging ??

Why would it affect the speed of dragging? It is important for rotation of the canvas (it is rotated around the centre), nothing else.

[jacek]

The problem is occuring when i change the loop , making the middle cordinates as top left.

Do I understand you correctly, that if you change that loop back to original version and recompile the example, it works faster?

[aamer4yu]

@wysota even i want to know why was it affetcing the speed while dragging the chips..
u can try urself...

@jacek u r right... the original works fine,,, but whne i change it, the dragging becomes slow .. i amnot able to logically make out why is it happening

[wysota]

@wysota even i want to know why was it affetcing the speed while dragging the chips..
u can try urself...

@jacek u r right... the original works fine,,, but whne i change it, the dragging becomes slow .. i amnot able to logically make out why is it happening

It works fine for me... I don't experience any slowdowns.

[jacek]

It works fine for me... I don't experience any slowdowns.

For me too. I have both versions running side by side and I don't see any difference.

[wysota]

Something else must have been changed in the code.

@aamer4yu: Could you make a diff of the source code to see if there are any other differences outside the loop?