Question about screen transition

[L4Y]

I am working on a custom board with TouchGFX, and the custom board connects to a SPI LCD. I found an issue that TouchGFX will call flushFrameBuffer(const touchgfx::Rect& rect) function twice when making a screen transition. I just wondering if the behavior is normal, and why.

Best Regards!

[Martin KJELDSEN]

Hi L4Y,

I'm assuming this is a screen transition with no effct (Slide, Cover) and you're wondering why we're trying to transfer the same framebuffer contents twice?

Is rect identical between calls?

/Martin

[L4Y]

Hi Martin,

Yes, it's exactly as what you said. And the size of the Rect is always full screen between each calls when making screen transition

Best Regards!

[L4Y]

@Martin KJELDSEN​ 

Hi Martin,

Any update about the issue?

Best Regards!

[Martin KJELDSEN]

Hi @L4Y​,

I think it's because, usually, if people use an animation to transfer to a different screen, the very last frame of that animation will be the same as the screen being switched in. For noTransition this essentially the same, since there's just 1 step to the transition and then the new frame.

This may be something we haven't thought fully through for flushFrameBuffer(). I suppose what you could do is remember if you've already transferred a particular Rect within a certain frame. Then don't do that again.

Does that make sense?

/Martin

[L4Y]

Hi Martin,

I don't think we could know the particular frame that we've already transferred since we just know the size of Rect from flushFrameBuffer() perspective.

Best Regards

[Martin KJELDSEN · Accepted solution]

You can override beginFrame() and endFrame() in your concrete hal:

void MyHal::beginFrame()
{
    //set some global variable here. In flushFrameBuffer() check if you're transferring the same frame twice.
 
   HAL::beginFrame();
}

If the frame number is different then it's a problem we have to solve in TouchGFX unless you want to compare the entire Rect with what's in the other framebuffer. Not a good idea.

Edit: This is verified in 4.10.0 and will be fixed. Until then you can use the above to ensure that you're only transferring the same frame once.

/Martin

[L4Y]

Hi Martin,

Yes, that's maybe a workaround even though it's not perfect. Hope it can be improved in next TouchGFX release.

Best Regards!

[Martin KJELDSEN]

Right. I'll investigate whether or not we're 100% right in our assumptions here 🙂 And then it will definitely be improved.

/Martin

[Martin KJELDSEN]

Hi again,

Okay, verified. We're working on a fix.

/Martin