- Qt 5.5
- Qt Graphical Effects
- QML Types
- Glow QML Type
- Qt 5.5.1 Reference Documentation

# Glow QML Type

Generates a blurred and colorized image of the source and places it behind the original, giving impression that the source is glowing. More...

Import Statement: | import QtGraphicalEffects 1.0
Since: | QtGraphicalEffects 1.0

- List of all members, including inherited members

## Properties

- cached : bool
- color : color
- fast : bool
- radius : real
- samples : int
- source : variant
- spread : real
- transparentBorder : bool

## Detailed Description

By default effect produces a high quality glow image, thus the rendering speed of the effect may not be the highest possible. The rendering speed is reduced especially if the glow edges are heavily softened. For use cases that require faster rendering speed and the highest possible visual quality is not necessary, property fast can be set to true.

Source | Effect applied
--- | ---

## Example

The following example shows how to apply the effect.

    import QtQuick 2.0
    import QtGraphicalEffects 1.0

    Item {
        width: 300
        height: 300

        Rectangle {
            anchors.fill: parent
            color: "black"
        }

        Image {
            id: butterfly
            source: "images/butterfly.png"
            sourceSize: Qt.size(parent.width, parent.height)
            smooth: true
            visible: false
        }

        Glow {
            anchors.fill: butterfly
            radius: 8
            samples: 16
            color: "white"
            source: butterfly
        }
    }

## Property Documentation

cached : bool

This property allows the effect output pixels to be cached in order to improve the rendering performance.

Every time the source or effect properties are changed, the pixels in the cache must be updated. Memory consumption is increased, because an extra buffer of memory is required for storing the effect output.

It is recommended to disable the cache when the source or the effect properties are animated.

By default, the property is set to `false`.

color : color

This property defines the RGBA color value which is used for the glow.

By default, the property is set to `"white"`.

Output examples with different color values |  |
--- | --- | ---
color: #ffffff | color: #00ff00 | color: #aa00ff00
radius: 8 | radius: 8 | radius: 8
samples: 16 | samples: 16 | samples: 16
spread: 0.5 | spread: 0.5 | spread: 0.5

fast : bool

This property selects the blurring algorithm that is used to produce the softness for the effect. Setting this to true enables fast algorithm, setting value to false produces higher quality result.

By default, the property is set to `false`.

Output examples with different fast values |  |
--- | --- | ---
fast: false | fast: true
radius: 16 | radius: 16
samples: 24 | samples: 24
color: #ffffff | color: #ffffff
spread: 0.3 | spread: 0.3

radius : real

Radius defines the softness of the glow. A larger radius causes the edges of the glow to appear more blurry.

Depending on the radius value, value of the samples should be set to sufficiently large to ensure the visual quality.

The value ranges from 0.0 (no blur) to inf. By default, the property is set to `0.0` (no blur).

Output examples with different radius values |  |
--- | --- | ---
radius: 0 | radius: 6 | radius: 12
samples: 24 | samples: 24 | samples: 24
color: #ffffff | color: #ffffff | color: #ffffff
spread: 0 | spread: 0 | spread: 0

samples : int

This property defines how many samples are taken per pixel when edge softening blur calculation is done. Larger value produces better quality, but is slower to render.

Ideally, this value should be twice as large as the highest required radius value, for example, if the radius is animated between 0.0 and 4.0, samples should be set to 8.

The value ranges from 0 to 32. By default, the property is set to `0`.

This property is not intended to be animated. Changing this property may cause the underlying OpenGL shaders to be recompiled.

When fast property is set to true, this property has no effect.

source : variant

This property defines the source item that is going to be used as source for the generated glow.

Note: It is not supported to let the effect include itself, for instance by setting source to the effect's parent.

spread : real

This property defines how large part of the glow color is strenghtened near the source edges.

The values range from 0.0 to 1.0. By default, the property is set to `0.5`.

Output examples with different spread values |  |
--- | --- | ---
spread: 0.0 | spread: 0.5 | spread: 1.0
radius: 8 | radius: 8 | radius: 8
samples: 16 | samples: 16 | samples: 16
color: #ffffff | color: #ffffff | color: #ffffff

transparentBorder : bool

This property determines whether or not the effect has a transparent border.

When set to `true`, the exterior of the item is padded with a 1 pixel wide transparent edge, making sampling outside the source texture use transparency instead of the edge pixels. Without this property, an image which has opaque edges will not get a blurred edge.

In the snippet below, the Rectangle on the left has transparent borders and has blurred edges, whereas the Rectangle on the right does not.

    import QtQuick 2.0
    import QtGraphicalEffects 1.0

    Rectangle {
        width: 180
        height: 100

        Row {
            anchors.centerIn: parent
            spacing: 16

            Rectangle {
                id: normalRect
                width: 60
                height: 60
                color: "#444"

                layer.enabled: true

                layer.effect: Glow {
                    radius: 4
                    samples: radius * 2
                    source: normalRect
                    color: "steelblue"
                }
            }

            Rectangle {
                id: transparentBorderRect
                width: 60
                height: 60
                color: "#444"

                layer.enabled: true

                layer.effect: Glow {
                    radius: 4
                    samples: radius * 2
                    source: transparentBorderRect
                    color: "steelblue"
                    transparentBorder: true
                }
            }
        }
    }

[Missing image transparentBorder.png]