Hello,
We have a Quick scene where we draw a lot of semi-transparent rectangles and
those rectangles are rounded in one side. As a representative :
Rectangle { id: clipper width: 100 height: 100 opacity: 0.5
clip: true
Rectangle { id: clipped radius: 20.0 width:
parent.width + radius height: parent.height color: 'red' }}
As it can be seen from the snippet above we use clipping to achieve rounding in
one side however that comes with a significant cost in batching as the number
of those rectangles are quite high. I've looked at what we can do to get rid of
clipping while preserving the existing and UI what I've found is as follows:
Using Canvas API in QMLThis will probably be slower than QQuickRectangle with
clipping.
Using QQuickPaintedItem with QPainter APIThis will be faster than canvas API
but still slower than QQuickRectangle with clipping.
Custom QQuickItemThis seems like the only way we can outperform QQuickRectangle
with clipping however the amount of implementation needed for a simple rounded
rectangle makes me think twice about this approach. TBH I'm also a bit scared
about some potential issues like aliasing.
Using OpacityMask from QtGraphicalEffectsI am not sure about this approach. Can
you shed some light on how this works behind the scenes in scene graph renderer
if I have, let's say, a hundred instances of the following :
Rectangle { // some properties
OpacityMask { // some properties }}
As far as I understand each shader is a unique state in graphics API which
results in a separate draw call but is it also the case if we use the same
shader for repeated items like above ?
I mean this should be fine if the shader is set for once because I assume items
can be batched afterwards. But if each item requires a different batch then
this has no gain over clipping.
Am I correct about the assumptions I make above regarding the performance
characteristics ? What is the best way to deal with this ?
Thank you.
Murat Seker
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