On 04/05/2013 19:30, Preet wrote:
Hi,
I have a couple of questions regarding images in QtQuick2.
1.
For a resolution independent application, I tried using several images
(all 128x128px) that I scaled as appropriate for target devices. In
QtQuick1 this didn't work out so well -- scaling the images was
expensive and made the application slow.
Can I expect image resizing/drawing to be much faster in QtQuick2? If
the images are directly uploaded as textures to OpenGL without being
scaled down CPU-side I'd imagine this to be the case.
Correct, scaling of images should essentially be free as this will be
performed in hardware.
2.
I'd like to use ShaderEffects to apply a somewhat trivial shader to
most of the images in my application. The images are black and white
icons, and I'd like to use shaders to change the black and white
output fragments to different colors (ie maybe blue and green, red and
yellow, etc).
The shader itself is super simple and probably adds negligable cost to
the pipeline, but I'm concerned about how overall performance would be
affected compared to the default method QtQuick uses to render a bunch
of images.
Would QtQuick still intelligently batch the images and draw them using
only a few calls? Or would it individually bind the same shader and
issue a separate draw call for each image?
Using a ShaderEffect item implies rendering the source to a texture via
an FBO and then applying the effect's shaders to the resulting texture.
Therefore using many ShaderEffects will produce a performance impact at
some point. If you really have many of these items to show it would be
better to implement a custom item using the scene graph api. Take the
existing QSGSimpleTextureNode or image item as starting points and
provide a custom material that renders using your colourisation shader.
This way you avoid the FBO pass for each item.
Hope this helps,
Sean
Preet
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Klarälvdalens Datakonsult AB, a KDAB Group company
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