[SailfishDevel] Different behaviour of ShaderEffectSource in emulator vs. device

Gunnar Sletta gunnar.sletta at jolla.com
Wed Feb 11 19:07:36 UTC 2015


On 11 Feb 2015, at 10:46, Luca Donaggio <donaggio at gmail.com<mailto:donaggio at gmail.com>> wrote:

Thank you Gunnar!

I completely misunderstood the "layer" property of the Item element! I thought its purpouse was to apply an effect (or a texture) to an Item before rendering it on the scene, not to render any Item as an out-of-scene texture which could then be used as the source for a ShaderEffect!

A convenient way of adding an effect is one usecase certainly. You can use it for other things though. The Qt 5.4 docs should have a fairly good explanation of how it works.  http://doc-snapshot.qt-project.org/qt5-5.4/qml-qtquick-item.html#item-layers

I thought that's what ShaderEffectSource does!

layer is a more convenient ShaderEffectSource which doesn’t require you to add items into the sibling hierarchy.


In my defense I must say that Qt documentation is not very clear, nor there are many examples available :-)

In pre Qt 5.4, yes. Very much so :) If you find the 5.4 docs lacking, please let me know.


Just out of curiosity then: why do you think my first code example works in the Emulator?

Using the FBO as a source texture while writing to it is supported on many graphics cards.



On Tue, Feb 10, 2015 at 9:04 PM, Gunnar Sletta <gunnar.sletta at jolla.com<mailto:gunnar.sletta at jolla.com>> wrote:
Hi Luca,

The application code is not doing the right thing :)

If the ShaderEffectSource depends on itself, it needs to have the “recursive” property set to true, and that is still probably not what you want. What you probably want is to set “layer.enabled: true; layer.smooth: true” on the gradientSource and then use it directly in the ShaderEffect. That should do what you want and comes without consequence.

cheers,
Gunnar


On 10 Feb 2015, at 11:54, Luca Donaggio <donaggio at gmail.com<mailto:donaggio at gmail.com>> wrote:

Thanks Andrey.

I'll report this on TJC as well, trying to get more visibility. I hope that some Sailor will notice it: it's not that important, but it's disturbing nonetheless.


On Tue, Feb 10, 2015 at 11:39 AM, Andrey Kozhevnikov <coderusinbox at gmail.com<mailto:coderusinbox at gmail.com>> wrote:
yes i can confirm this behaviour.

10.02.2015 15:24, Luca Donaggio пишет:
Hi Andrey, thanks for your reply.

Still, can you try both tests on your Jolla?
The first shouldn't work, while the second does.

On Tue, Feb 10, 2015 at 10:32 AM, Andrey Kozhevnikov <coderusinbox at gmail.com<mailto:coderusinbox at gmail.com>> wrote:
sorry, not using emulator at all.

10.02.2015 14:28, Luca Donaggio пишет:
Anybody is willing to try my test code and confirm or deny my finding?

On Fri, Feb 6, 2015 at 2:12 PM, Luca Donaggio <donaggio at gmail.com<mailto:donaggio at gmail.com>> wrote:
The following code works fine in Emulator, changing the gradient of the Rectangle correctly updates the nested ShaderEffectSource and it is reflected on the ShaderEffect which uses it as its texture:

Page {
    id: page

    SilicaFlickable {
        anchors.fill: parent

        contentHeight: column.height

        Column {
            id: column

            anchors { top: parent.top; left: parent.left; right: parent.right; leftMargin: Theme.paddingLarge; rightMargin: Theme.paddingLarge; }
            spacing: Theme.paddingLarge

            PageHeader {
                title: qsTr("ShaderEffect Test")
            }

            Row {
                anchors.horizontalCenter: parent.horizontalCenter
                spacing: Theme.paddingLarge

                Column {
                    spacing: Theme.paddingSmall

                    Rectangle {
                        id: gradientSource

                        property list<Gradient> gradients: [
                            Gradient {
                                GradientStop { position: 0.0; color: "black"; }
                                GradientStop { position: 1.0; color: "blue"; }
                            },

                            Gradient {
                                GradientStop { position: 0.0; color: "black"; }
                                GradientStop { position: 1.0; color: "red"; }
                            }
                        ]

                        width: 100
                        height: 100

                        gradient: gradients[0]

                        ShaderEffectSource {
                            id: gradientTexture

                            anchors.fill: parent
                            sourceItem: gradientSource
                            hideSource: false
                            live: true
                        }
                    }

                    Label {
                        font.pixelSize: Theme.fontSizeExtraSmall
                        wrapMode: Text.WordWrap
                        text: "Rectangle\nShaderEffectSource"
                    }
                }

                Column {
                    spacing: Theme.paddingSmall

                    ShaderEffect {
                        property variant source: gradientTexture

                        width: 100
                        height: 100

                        blending: false
                        cullMode: ShaderEffect.BackFaceCulling
                        fragmentShader: "
                            varying highp vec2 qt_TexCoord0;
                            uniform lowp float qt_Opacity;
                            uniform sampler2D source;

                            void main() {
                                gl_FragColor = texture2D(source, qt_TexCoord0) * qt_Opacity;
                            }"
                    }

                    Label {
                        font.pixelSize: Theme.fontSizeExtraSmall
                        text: "ShaderEffect"
                    }
                }
            }

            Button {
                anchors.horizontalCenter: parent.horizontalCenter
                text: "Blue gradient"

                onClicked: gradientSource.gradient = gradientSource.gradients[0]
            }

            Button {
                anchors.horizontalCenter: parent.horizontalCenter
                text: "Red gradient"

                onClicked: gradientSource.gradient = gradientSource.gradients[1]
            }
        }
    }
}

It doesn't work on device though (changing Reactangle's gradient doesn't update the ShaderEffectSource).

Un-nesting the ShaderEffectSource from its source item (the Rectangle) works fine both on emulator and on device:

Page {
    id: page

    SilicaFlickable {
        anchors.fill: parent

        contentHeight: column.height

        Column {
            id: column

            anchors { top: parent.top; left: parent.left; right: parent.right; leftMargin: Theme.paddingLarge; rightMargin: Theme.paddingLarge; }
            spacing: Theme.paddingLarge

            PageHeader {
                title: qsTr("ShaderEffect Test")
            }

            Row {
                anchors.horizontalCenter: parent.horizontalCenter
                spacing: Theme.paddingLarge

                Column {
                    spacing: Theme.paddingSmall

                    Rectangle {
                        id: gradientSource

                        property list<Gradient> gradients: [
                            Gradient {
                                GradientStop { position: 0.0; color: "black"; }
                                GradientStop { position: 1.0; color: "blue"; }
                            },

                            Gradient {
                                GradientStop { position: 0.0; color: "black"; }
                                GradientStop { position: 1.0; color: "red"; }
                            }
                        ]

                        width: 100
                        height: 100

                        gradient: gradients[0]
                    }

                    Label {
                        font.pixelSize: Theme.fontSizeExtraSmall
                        text: "Rectangle"
                    }
                }

                Column {
                    spacing: Theme.paddingSmall

                    ShaderEffectSource {
                        id: gradientTexture

                        width: 100
                        height: 100
                        sourceItem: gradientSource
                        hideSource: false
                        live: true
                    }

                    Label {
                        font.pixelSize: Theme.fontSizeExtraSmall
                        text: "ShaderEffectSource"
                    }
                }

                Column {
                    spacing: Theme.paddingSmall

                    ShaderEffect {
                        property variant source: gradientTexture

                        width: 100
                        height: 100

                        blending: false
                        cullMode: ShaderEffect.BackFaceCulling
                        fragmentShader: "
                            varying highp vec2 qt_TexCoord0;
                            uniform lowp float qt_Opacity;
                            uniform sampler2D source;

                            void main() {
                                gl_FragColor = texture2D(source, qt_TexCoord0) * qt_Opacity;
                            }"
                    }

                    Label {
                        font.pixelSize: Theme.fontSizeExtraSmall
                        text: "ShaderEffect"
                    }
                }
            }

            Button {
                anchors.horizontalCenter: parent.horizontalCenter
                text: "Blue gradient"

                onClicked: gradientSource.gradient = gradientSource.gradients[0]
            }

            Button {
                anchors.horizontalCenter: parent.horizontalCenter
                text: "Red gradient"

                onClicked: gradientSource.gradient = gradientSource.gradients[1]
            }
        }
    }
}

Is it a bug?

--
Luca Donaggio



--
Luca Donaggio



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--
Luca Donaggio



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--
Luca Donaggio
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Luca Donaggio
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