縮放數百個QGraphicItems的高效方法

Question

我有一個可縮放的QGraphicsView，場景包含數百（甚至數千）個數據點。積分由QGraphicsEllipseItem s表示並收集到QGraphicsItemGroup中。當視圖放大時，我希望數據點保持恆定的大小（即，相鄰點之間的距離增加，但大小保持不變）。現在我通過每一個用戶放大時間運行此代碼實現這一點：

#get all the QGraphicsEllipseItems that make up the QGraphicsItemGroup 
children = graphics_item_group.childItems() 
for c in children: 
    #base_size_x and base_size_y are the sizes of the 
    #untrasformed ellipse (on the scene) when zoom factor is 1 
    #New width and height are obtained from the original sizes and 
    #the new zoom factors (h_scale, v_scale) 
    new_width = base_size_x/h_scale 
    new_height = base_size_y/v_scale 

    #The top-left corner of the new rectangle for the item has to be recalculated 
    #when scaling in order to keep the center at a constant position 
    #For this, the center of the item has to be stored first 
    old_center_x = c.rect().center().x() 
    old_center_y = c.rect().center().y() 

    #New coordinates of the rectangle top left point are calculated 
    new_topleft_x = old_center_x - new_width/2. 
    new_topleft_y = old_center_y - new_height/2. 

    #Finally a new rectangle is set for the ellipse 
    c.setRect(new_topleft_x, new_topleft_y, new_width, new_height) 

此代碼的工作。問題在於它非常緩慢（沒有補償縮放放大/縮小非常平滑）。我試圖關閉視圖的抗鋸齒功能，但它使事情看起來非常難看。還有什麼我可以做的，使處理/重繪速度更快？

Answer 1

在的QGraphicsItem的構造函數：

setFlag(ItemIgnoresTransformations); 

放大時，該項目將保持相同的大小，以及你將不必手動縮放。