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@ -48,7 +48,7 @@
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application window.
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We will first review the \c Mouse class to see how to animate
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items and detect item collision, and then we will review the \c
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items and detect item collisions, and then we will review the \c
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main() function to see how to put the items into a scene and how to
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implement the corresponding view.
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@ -90,7 +90,7 @@
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calling the item's \l {QGraphicsItem::setRotation()}{setRotation()} function
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we alter the direction in which the mouse will start moving.
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When the QGraphicsScene decides to advance the scene a frame it will
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When the QGraphicsScene decides to advance the scene by a frame, it will
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call QGraphicsItem::advance() on each of the items. This enables us to
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animate our mouse using our reimplementation of the advance() function.
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@ -98,10 +98,10 @@
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\snippet graphicsview/collidingmice/mouse.cpp 5
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\snippet graphicsview/collidingmice/mouse.cpp 6
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First, we don't bother doing any advance if the step is 0 since we want to our advance in
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the actual advance (advance() is called twice, once with step == 0 indicating that items
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are about to advance and with step == 1 for the actual advance). We also ensure that the
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mice stays within a circle with a radius of 150 pixels.
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First, we don't bother doing any advance if the step is \c 0. This is because
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advance() is called twice: once with step == \c 0, indicating that items
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are about to advance, and then with step == \c 1 for the actual advance.
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We also ensure that the mouse stays within a circle with a radius of 150 pixels.
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Note the \l {QGraphicsItem::mapFromScene()}{mapFromScene()}
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function provided by QGraphicsItem. This function maps a position
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@ -126,7 +126,7 @@
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the parent's coordinate system. For items with no parent, the
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given position is interpreted as scene coordinates. QGraphicsItem
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also provides a \l {QGraphicsItem::}{mapToParent()} function to
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map a position given in item coordinates, to the parent's
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map a position given in item coordinates to the parent's
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coordinate system. If the item has no parent, the position will be
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mapped to the scene's coordinate system instead.
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@ -140,7 +140,7 @@
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defines the outer bounds of the item as a rectangle. Note that the
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Graphics View framework uses the bounding rectangle to determine
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whether the item requires redrawing, so all painting must be
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restricted inside this rectangle.
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done inside this rectangle.
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\snippet graphicsview/collidingmice/mouse.cpp 3
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@ -148,7 +148,7 @@
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{QGraphicsItem::paint()}{paint()} function to paint the contents
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of the item; the function paints the item in local coordinates.
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Note the painting of the ears: Whenever a mouse item collides with
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Note the painting of the ears: whenever a mouse item collides with
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other mice items its ears are filled with red; otherwise they are
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filled with dark yellow. We use the
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QGraphicsScene::collidingItems() function to check if there are
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@ -166,17 +166,15 @@
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{QGraphicsItem::collidesWithItem()}{collidesWithItem()} function
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to provide your own custom item and shape collision algorithm.
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This completes the \c Mouse class implementation, it is now ready
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This completes the \c Mouse class implementation; it is now ready
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for use. Let's take a look at the \c main() function to see how to
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implement a scene for the mice and a view for displaying the
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contents of the scene.
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\section1 The Main() Function
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In this example we have chosen to let the \c main() function
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provide the main application window, creating the items and the
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scene, putting the items into the scene and creating a
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corresponding view.
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The \c main() function provides the main application window,
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as well as creating the items, their scene, and a corresponding view.
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\snippet graphicsview/collidingmice/main.cpp 0
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@ -192,18 +190,18 @@
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The QGraphicsScene class serves as a container for
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QGraphicsItems. It also provides functionality that lets you
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efficiently determine the location of items as well as determining
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which items that are visible within an arbitrary area on the
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which items are visible within an arbitrary area on the
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scene.
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When creating a scene it is recommended to set the scene's
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rectangle, i.e., the rectangle that defines the extent of the
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rectangle; the rectangle that defines the extent of the
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scene. It is primarily used by QGraphicsView to determine the
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view's default scrollable area, and by QGraphicsScene to manage
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item indexing. If not explicitly set, the scene's default
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rectangle will be the largest bounding rectangle of all the items
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on the scene since the scene was created (i.e., the rectangle will
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grow when items are added or moved in the scene, but it will never
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shrink).
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on the scene since the scene was created. This means that the
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rectangle will grow when items are added or moved in the scene,
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but it will never shrink.
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\snippet graphicsview/collidingmice/main.cpp 2
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@ -213,8 +211,8 @@
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searched. Adding, moving and removing items, however, is done in
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constant time. This approach is ideal for dynamic scenes, where
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many items are added, moved or removed continuously. The
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alternative is \l {QGraphicsScene::BspTreeIndex}{BspTreeIndex}
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which makes use of binary search resulting in item location
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alternative is \l {QGraphicsScene::BspTreeIndex}{BspTreeIndex},
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which makes use of a binary search to achieve item location
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algorithms that are of an order closer to logarithmic complexity.
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\snippet graphicsview/collidingmice/main.cpp 3
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@ -223,9 +221,9 @@
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\snippet graphicsview/collidingmice/main.cpp 4
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To be able to view the scene we must also create a QGraphicsView
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To be able to view the scene, we must also create a QGraphicsView
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widget. The QGraphicsView class visualizes the contents of a scene
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in a scrollable viewport. We also ensure that the contents is
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in a scrollable viewport. We also ensure that the contents are
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rendered using antialiasing, and we create the cheese background
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by setting the view's background brush.
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@ -240,14 +238,14 @@
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Then we set the cache mode; QGraphicsView can cache pre-rendered
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content in a pixmap, which is then drawn onto the viewport. The
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purpose of such caching is to speed up the total rendering time
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for areas that are slow to render, e.g., texture, gradient and
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for areas that are slow to render, for example: texture, gradient, and
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alpha blended backgrounds. The \l
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{QGraphicsView::CacheMode}{CacheMode} property holds which parts
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of the view that are cached, and the \l
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of the view are cached, and the \l
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{QGraphicsView::CacheBackground}{CacheBackground} flag enables
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caching of the view's background.
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By setting the \l {QGraphicsView::dragMode}{dragMode} property we
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By setting the \l {QGraphicsView::dragMode}{dragMode} property, we
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define what should happen when the user clicks on the scene
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background and drags the mouse. The \l
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{QGraphicsView::ScrollHandDrag}{ScrollHandDrag} flag makes the
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@ -264,9 +262,9 @@
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advance() slot of the scene. Every time the timer fires, the scene
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will advance one frame.
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We then tell the timer to fire every 1000/33 millisecond. This will
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We then tell the timer to fire every 1000/33 milliseconds. This will
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give us a frame rate of 30 frames a second, which is fast enough for most
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animations. Doing the animation with a single timer connect to advance the
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animations. Doing the animation with a single timer connection to advance the
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scene ensures that all the mice are moved at one point and, more
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importantly, only one update is sent to the screen after all the mice have
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moved.
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