[Interest] use custom fragment shader for Quick2 Image item

Sletta Gunnar Gunnar.Sletta at digia.com
Wed Oct 23 07:39:05 CEST 2013

You can use a ShaderEffect element. It does not use an FBO for plain Image types.

Image {
    id: myImage
    visible: false

ShaderEffect {
    property variant source: myImage
    anchors.fill: myImage
    fragmentShader: "
        varying highp vec2 qt_TexCoord0;
        uniform lowp vec4 sampler2D source;
        void main() {
            gl_FragColor = texture2D(source, qt_TexCoord0).rrra;

In Qt 5.0 and 5.1 this will use the texture directly without any extra copies. In 5.2 the image's texture might be in an atlas and will currently be copied out of the atlas into its own texture which is then used directly. I want to add some performance hints to the ShaderEffect to avoid the copy-out-of-the-atlas (which is needed for compatibility right now), but I'm not sure those will make 5.2.

The other alternative is to implement a custom material using the QSG API directly. Then you get the best possible performance.


Fra: interest-bounces+gunnar.sletta=digia.com at qt-project.org [interest-bounces+gunnar.sletta=digia.com at qt-project.org] på vegne av Ola Røer Thorsen [ola at silentwings.no]
Sendt: 22. oktober 2013 15:20
To: interest at qt-project.org
Emne: [Interest] use custom fragment shader for Quick2 Image item

Hi all,

I want to use a custom fragment shader when rendering a Image item. Is it possible to set the shader to use directly somehow? That is, I want to use a custom shader instead of the "passthrough" fragment shader used in the Image element.

I have tried using the QtGraphicalEffects (GammaAdjust), but the performance is not good enough on my target platform (Omap 3530). ShaderEffect elements work, but they also seem to render via another render-texture, again with a performance loss.

Best regards,

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