Highlight hovered cells in QGraphicsScene

occohd21

I am trying to highlight hovered cells on a Grid drawn in a QGraphicsScene.

Previously I had tried to add another transparent QWidget to the Scene, so that this new QWidget is shown above the Scenes drawing.
I tried it like this without any success. The Overlay Widget is never visible as it is covered by the Scenes drawing

self.__scene = QtWidgets.QGraphicsScene(self)
        self.__view = QtWidgets.QGraphicsView(self.__scene, self)
        self.__overlay = QWidget() # must be toplevel it seems
        self.__scene.addWidget(self.__overlay)

As a workaround I thought that I can just draw both the Grid AND the Highlight effect (blue rect around the cell) on the Scene. My code now looks as follows. But the problem is, that I will always have to redraw the Highlight when the Grid was redrawn. Apparently the newly drawn Grid will draw over my Highlight. This just feels super hacky

def __drawGrid(self):
        if self.__grid_cells:
            # remove prev. grid from scene
            self.__scene.removeItem(self.__grid_cells)
            # remove last reference for gc
            self.__grid_cells = None
        # create new grid
        self.__grid_cells = QGraphicsItemGroup()
        for row_idx, row in enumerate(self.__pattern_model.get_cells()):
            for stitch_idx, stitch in enumerate(row):
                x1 = stitch_idx * self.__cell_width
                y1 = row_idx * self.__cell_height
                if stitch:
                    pen = QPen(Qt.white, 1, Qt.SolidLine)
                    brush = QBrush(Qt.black)
                else:
                    pen = QPen(Qt.black, 1, Qt.SolidLine)
                    brush = QBrush(Qt.white)
                self.__grid_cells.addToGroup(
                    self.__scene.addRect(
                        x1, y1, self.__cell_width, self.__cell_height, pen, brush
                    )
                )
        self.__scene.addItem(self.__grid_cells)
        # redraw highlight to put it on top again
        self.__redraw_highlight()

    def __redraw_highlight(self):
        if self.highlighted_cell:
            self.__scene.removeItem(self.highlighted_cell)
        self.__scene.addItem(self.highlighted_cell)

    def __drawHighlight(self, stitch_idx, row_idx):
        if self.highlighted_cell:
            self.__scene.removeItem(self.highlighted_cell)
        x1 = stitch_idx * self.__cell_width
        y1 = row_idx * self.__cell_height
        pen = QPen(Qt.blue, 5, Qt.SolidLine)
        self.highlighted_cell = self.__scene.addRect(
            x1, y1, self.__cell_width, self.__cell_height, pen
        )

Is the way I am doing it right now completely wrong? Are there any best or even just better practices for this?

SGaist

Hi,

Why not use a QRubberBand and move it where you want without adding it to the scene ?

JonB

@occohd21
I see you adding widgets. rectangles and groups. I don't know what your grid is for, but did you at least consider doing it all via drawBackground()? That's how I do things like this, and for temporary highlighting I use drawForeground(), with a semi-transparent color. There is no adding & removing graphics items. It's a very different approach, depends on your usage.

occohd21

@SGaist Thanks for your answer. I did it that way :)