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How do you draw a grid and rectangles in Python?

Answer 1

A:

Those actions are not that difficult. All you really need for that is hit detection, which is not hard (is the cursor over the correct area? Okay, perform the operation then). The harder part is finding an appropriate canvas widget for the toolkit in use.

Ignacio Vazquez-Abrams 2010-08-21 20:18:04

@Ignacio Vazquez-Abrams: For Tkinter what you say is the hard part is pretty easy: use the Canvas widget.

Bryan Oakley 2010-08-22 19:03:37

Answer 2

A:

The DiagramScene Eaxmple that comes with PyQt implements much of the functionality you want. It has a fixed background grid, you can create a rectangle object but it's not resizable and doesn't snap to grid.

This SO article has advice on resizing graphical objects with the mouse. It's for C++ Qt but the technique should be easy to replicate in PyQt.

For snap-to-grid I don't think there is any built-in functionality. You would probably need to reimplement the itemChange(GraphicsItemChange change, const QVariant &value) function. Pseudocode:

if (object not possitioned exactly on the grid):
    (possition the item on the grid)

Repossitioning the item will cause itemChange to get called again, but that's ok because the item will be possitioned correctly and won't be moved again, so you'll not be stuck in an endless loop.

Simon Hibbs 2010-08-23 09:05:47

The DiagramScene example repeats an image to create a grid. It may or may not be difficult to snap objects to such a grid.

Winston C. Yang 2010-08-24 13:44:09

That's true, perhaps better to create a grid of squares. I do that in one of my apps using a QGraphicsItemGroup with each grid cell belonging to the group.

Simon Hibbs 2010-08-24 16:14:30

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How do you draw a grid and rectangles in Python?

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