How to swap QGraphicsRectItems on scene(changing theirs position)

lete

Hello,
I'm creating a visualization of sorting algorithms. I've got a vector of QGraphicsRectItems which are columns with different height and the same width, generated on the app start. They are being shuffled and then added to a QGraphicsScene. Class named "algorithms" sort a vector of float values which are use to set a height of columns. On swap - it emits a signal to a main class with two integers, so it looks like this:

emit comparision(array[first element to swap], array[second element to swap]);

Function(on_comparison) in main class is connected with that signal. Problem appeared when I was trying to swap these 2 elements. I've created a variable to set a n column position to it. After that I was trying to setPos of columns so I did something like:

void on_comparision(int n, int k)
{
   auto nColumnPos = columns[n]->pos().x();
   columns[n]->setX(columns[k]->pos().x());
   columns[k]->setX(nColumnPos);
   std::swap(columns[n], columns[k]);
}

But it doesn't work. Positions are not changing. Furthermore

qDebug() <<nColumnPos;

shows value = 0.

I was wondering if my whole program works so I decided to implement 2 sorting algorithms which swap 2 near each other elements and modified on_comparison function to

columns[n]->setX(columns[n].pos().x() + columnsWidth);
columns[n]->setX(columns[n].pos().x() - columnsWidth);
std::swap(columns[n], columns[k]);

It works but doesn't give satisfying result. This function will work only with sorting algorithms that check elements 1 after another eg. bubble sort/cocktail sort. It will not work fine with any other sorting algorithm like Merge sort, or Quicksort.

I was searching for the answer but didn't find anything helpful.

source code online:
source code to download, with .pro, .ui and main.cpp files

Thank you in advance.

SGaist

Hi and welcome to devnet,

You didn't set the position of your items but only worked with their rectangle property so you can do something like:

auto nRect = columns[n]->rect();
auto kRect = columns[k]->rect();
auto nColumnPos = nRect.left();
nRect.moveLeft(kRect.left());
kRect.moveLeft(nColumnPos);

columns[n]->setRect(nRect);
columns[k]->setRect(kRect);
std::swap(columns[n], columns[k]);

comparisions++;
ui->LabelComparisions_var->setNum(comparisions);

lete

@SGaist Oh that seems pretty obvious, what a shame I did not think about it. Thank you so much for helping me.

SGaist

You're welcome !

Since you have it working now, please mark the thread as solved using the "Topic Tools" button so that other forum users may know a solution has been found :)