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ParallaxScrollingBackground

The ParallaxScrollingBackground allows to create an endlessly scrollable background, usable by SideScroller games for example. More...

• List of all members, including inherited members

Properties

• image : alias
• mirrorSecondImage : bool
• movementVelocity : point
• ratio : point
• running : bool
• sourceImage2 : url
• sourceImage : url

Methods

• resetBackgrounds()

Detailed Description

The ParallaxScrollingBackground uses one or two MultiResolutionImage instances next to each other to create an endless scrollable background. This can be used to create a parallax scrolling background effect in a game. Make sure you read our tutorial about How to create mobile games for different screen sizes and resolutions to learn about the recommended size for your background images.

Mirrored Images

The property sourceImage needs to bet set or the item won't work correctly. If sourceImage2 is empty, the image declared in sourceImage is mirrored as second image. It is mirrored vertically when scrolling into y direction and horizontally when scrolling into x direction.

Every image could be mirrored, but only a correct prepared image looks well afterwards. Following picture shows an image which can be used for mirroring. Both sides have the same height at the left and right edge and a very similar appearance as seen on the left side. It will look great when Image1, Image2 and again Image1 are beside each other as seen on the right side.

In contrast to the correct image from above, the follwoing image illustrates an incorrect picture for endless scrolling. The background looks faulty when the edges and appearance do not fit accordingly as seen on the left side. The incorrect result can be seen on the right side.

Furthermore, mirroring images only effects the fluctuation of your image data and does not matter if the images are well prepared. To avoid this problem, you can create one image which is big enough and includes variation. You could also prepare two images which fit together as seen in the picture below. There is only one important criteria: The left edge of Image1 needs to fit together with the right edge of Image2 as seen on the left side. The images will fit perfectly together when Image1, Image2 and again Image1 are beside each other as seen on the right side.

Movement Support

The ParallaxScrollingBackground can only move either horizontally or vertically. Directional changes along one axis (e.g. changing from left to right) is supported. Changing from horizontal to vertical movement or vice versa is not supported.

Examples for supported directions:

• Left -> movementVelocity: Qt.point(10,0)
• Right -> movementVelocity: Qt.point(-10,0)
• Up -> movementVelocity: Qt.point(0,-10)
• Down -> movementVelocity: Qt.point(0,10)

Example Usage

Following examples demonstrate the usage of the ParallaxScrollingBackground.

Single Background Horizontal Movement

This example shows a single background image which leaves sourceImage2 empty to mirror sourceImage source file. The background scrolls with constant speed (10px per second) towards the left border with movementVelocity set to Qt.point(10,0). It scrolls with a ratio of 1/1 compared to its parent.

 import Felgo
 import QtQuick

 GameWindow {

   Scene {

     ParallaxScrollingBackground {
       movementVelocity: Qt.point(10,0)
       ratio: Qt.point(1.0,1.0)
       sourceImage: "../assets/img/background-mountains.png"
     }
   }
 }

Single Background Vertical Movement

This example shows a single background image which leaves sourceImage2 empty to mirror sourceImage source file. The background scrolls with constant speed (10px per second) towards the bottom border with movementVelocity set to Qt.point(0,10). It scrolls with a ratio of 1/1 compared to its parent.

 import Felgo
 import QtQuick

 GameWindow {

   Scene {

     ParallaxScrollingBackground {
       movementVelocity: Qt.point(0,10)
       ratio: Qt.point(1.0,1.0)
       sourceImage: "../assets/img/background-wood.png"
     }
   }
 }

Dual Background

This example shows two different backgrounds using sourceImage and sourceImage2. The background scrolls with constant speed (50px per second) towards the right border with movementVelocity set to Qt.point(-50,0). It scrolls with a ratio of 1/1 compared to its parent.

 import Felgo
 import QtQuick

 GameWindow {

   Scene {

     ParallaxScrollingBackground {
       movementVelocity: Qt.point(-50,0)
       ratio: Qt.point(1.0,1.0)
       sourceImage: "../assets/img/background-hills.png"
       sourceImage2: "../assets/img/background-hills2.png"
     }
   }
 }

Several ParallaxScollingBackgrounds

When a game should use different parallax effects it needs to use several items which move with different speeds. This case is demonstrated in this example.

 import Felgo
 import QtQuick

 GameWindow {

   Scene {

     ParallaxScrollingBackground {
       movementVelocity: Qt.point(100,0)
       ratio: Qt.point(0.5,1.0)
       sourceImage: "../assets/img/background-mountains.png"
     }

     ParallaxScrollingBackground {
       id: background1
       movementVelocity: Qt.point(-100,0)
       ratio: Qt.point(1.0,1.0)
       sourceImage: "../assets/img/background-hills.png"
     }

     ParallaxScrollingBackground {
       id: background2
       movementVelocity: Qt.point(10,0)
       ratio: Qt.point(1.3,1.0)
       sourceImage: "../assets/img/background-lawn.png"
     }

   } // end of Scene

 } // end of GameWindow

Also see the Parallax Test for more information about the correct usage of the ParallaxScrollingBackground.

Property Documentation

 import Felgo
 import QtQuick

 GameWindow {

   Scene {
     ParallaxScrollingBackground {
       id: pxBg
       sourceImage: "../assets/img/background-wood.png"
       x: -(pxBg.image.width-scene.width)/2
       y: -(pxBg.image.height-scene.height)/2
       mirrorSecondImage: false
       movementVelocity: Qt.point(-75, 0)
     }
   } // end of Scene

 } // end of GameWindow

Method Documentation