DropShadow QML Type | Qt Graphical Effects 5.15.18

- Qt 5.15
- Qt Graphical Effects
- QML Types
- DropShadow QML Type
- Qt 5.15.18 Reference Documentation

# DropShadow QML Type

Generates a soft shadow behind the source item. More...

Import Statement: | import QtGraphicalEffects 1.15
Since: | QtGraphicalEffects 1.0

- List of all members, including inherited members

## Properties

- cached : alias
- color : alias
- horizontalOffset : real
- radius : int
- samples : alias
- source : alias
- spread : alias
- transparentBorder : alias
- verticalOffset : real

## Detailed Description

The DropShadow effect blurs the alpha channel of the input, colorizes the result and places it behind the source object to create a soft shadow. The shadow's color can be changed using the color property. The location of the shadow can be changed with the horizontalOffset and verticalOffset properties.

Source | Effect applied
--- | ---

The soft shadow is created by blurring the image live using a gaussian blur. Performing blur live is a costly operation. Fullscreen gaussian blur with even a moderate number of samples will only run at 60 fps on highend graphics hardware.

When the source is static, the cached property can be set to allocate another buffer to avoid performing the blur every time it is drawn.

Note: This effect is available when running with OpenGL.

## Example

The following example shows how to apply the effect.

     import QtQuick 2.12
     import QtGraphicalEffects 1.12

     Item {
         width: 300
         height: 300

         Rectangle {
             anchors.fill: parent
         }

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

         DropShadow {
             anchors.fill: butterfly
             horizontalOffset: 3
             verticalOffset: 3
             radius: 8.0
             samples: 17
             color: "#80000000"
             source: butterfly
         }
     }

## Property Documentation

cached : alias

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 : alias

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

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

Output examples with different color values |  |
--- | --- | ---
color: #000000 | color: #0000ff | color: #aa000000
radius: 8 | radius: 8 | radius: 8
samples: 17 | samples: 17 | samples: 17
horizontalOffset: 0 | horizontalOffset: 0 | horizontalOffset: 0
verticalOffset: 20 | verticalOffset: 20 | verticalOffset: 20
spread: 0 | spread: 0 | spread: 0

horizontalOffset : real

HorizontalOffset and verticalOffset properties define the offset for the rendered shadow compared to the DropShadow item position. Often, the DropShadow item is anchored so that it fills the source element. In this case, if the HorizontalOffset and verticalOffset properties are set to 0, the shadow is rendered exactly under the source item. By changing the offset properties, the shadow can be positioned relatively to the source item.

The values range from -inf to inf. By default, the properties are set to `0`.

Output examples with different horizontalOffset values |  |
--- | --- | ---
horizontalOffset: -20 | horizontalOffset: 0 | horizontalOffset: 20
radius: 4 | radius: 4 | radius: 4
samples: 9 | samples: 9 | samples: 9
color: #000000 | color: #000000 | color: #000000
verticalOffset: 0 | verticalOffset: 0 | verticalOffset: 0
spread: 0 | spread: 0 | spread: 0

radius : int

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

The ideal blur is achieved by selecting `samples` and `radius` such that `samples = 1 + radius * 2`, such as:

Radius | Samples
--- | ---
0 (no blur) | 1
1 | 3
2 | 5
3 | 7

By default, the property is set to `floor(samples/2)`.

Output examples with different radius values |  |
--- | --- | ---
radius: 0 | radius: 6 | radius: 12
samples: 25 | samples: 25 | samples: 25
color: #000000 | color: #000000 | color: #000000
horizontalOffset: 0 | horizontalOffset: 0 | horizontalOffset: 0
verticalOffset: 20 | verticalOffset: 20 | verticalOffset: 20
spread: 0 | spread: 0 | spread: 0

samples : alias

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 plus one, such as:

Radius | Samples
--- | ---
0 (no blur) | 1
1 | 3
2 | 5
3 | 7

By default, the property is set to `9`.

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

source : alias

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

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

spread : alias

This property defines how large part of the shadow color is strengthened near the source edges.

The value ranges from 0.0 to 1.0. By default, the property is set to `0.0`.

Output examples with different spread values |  |
--- | --- | ---
spread: 0.0 | spread: 0.5 | spread: 1.0
radius: 8 | radius: 8 | radius: 8
samples: 17 | samples: 17 | samples: 17
color: #000000 | color: #000000 | color: #000000
horizontalOffset: 0 | horizontalOffset: 0 | horizontalOffset: 0
verticalOffset: 20 | verticalOffset: 20 | verticalOffset: 20

transparentBorder : alias

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 shadow.

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

By default, this property is set to `true`.

     import QtQuick 2.12
     import QtGraphicalEffects 1.12

     Rectangle {
         width: 180
         height: 100

         Row {
             anchors.centerIn: parent
             spacing: 16

             Rectangle {
                 id: normalRect
                 width: 60
                 height: 60
                 radius: 10
                 color: "steelblue"
                 layer.enabled: true
                 layer.effect: DropShadow {
                     transparentBorder: false
                     horizontalOffset: 8
                     verticalOffset: 8
                 }
             }

             Rectangle {
                 id: transparentBorderRect
                 width: 60
                 height: 60
                 radius: 10
                 color: "steelblue"
                 layer.enabled: true
                 layer.effect: DropShadow {
                     transparentBorder: true
                     horizontalOffset: 8
                     verticalOffset: 8
                 }
             }
         }
     }

verticalOffset : real

HorizontalOffset and verticalOffset properties define the offset for the rendered shadow compared to the DropShadow item position. Often, the DropShadow item is anchored so that it fills the source element. In this case, if the HorizontalOffset and verticalOffset properties are set to 0, the shadow is rendered exactly under the source item. By changing the offset properties, the shadow can be positioned relatively to the source item.

The values range from -inf to inf. By default, the properties are set to `0`.

Output examples with different horizontalOffset values |  |
--- | --- | ---
horizontalOffset: -20 | horizontalOffset: 0 | horizontalOffset: 20
radius: 4 | radius: 4 | radius: 4
samples: 9 | samples: 9 | samples: 9
color: #000000 | color: #000000 | color: #000000
verticalOffset: 0 | verticalOffset: 0 | verticalOffset: 0
spread: 0 | spread: 0 | spread: 0