LabVIEW
How do I make a program to loop a video feed in LabVIEW 8.0?
To replicate the functionality of the missing Queue function "Lossy Enqueue", you ought to create a small subvi that checks the capacity of the queue, and first removes the oldest element from the queue if it is full before adding the latest image frame. This can be achieved using a combination of Get Queue Status, followed by Dequeue Element if the queue is full, then Enqueue Element.
The example you found (Queue stack - LIFO) simply demonstrates how to remove elements from the opposite end of the queue such that you receive them in the opposite order to that in which they are posted.
I havn't tested this, but I believe it should work.
This snapshot shows a subvi that will operate like a 'lossy enqueue' function.
It first checks the status of the queue. If the maximum capacity matches the number of elements in the queue, then it must be full, in which case it removes the oldest element. It then enqueues the new element.
I've used an image cluster as my element type, obviously you need to replace this with whatever element type you are using.
Thoric
You have to click the icon on the Front Panel, not the icon on the Block Diagram pane.
On second thoughts, to make this easier for you, don't create a subvi out of the code in my example, just place it directly into your main code. Doing this means the two "queue status" inputs simply come from your existing queue functions, and the third input (new image element) is simply your image as captured from your camera.
Although LabVIEW style guides recommend the use of subvis for making neater, easier to understand, reusable code segment, we'll let you off this time 😉
Ok, hopefully some guidance will help:
- The cluster you can see on my front panel for new image element is not the whole cluster, it actually contains a lot more than this but I reduced the amount of real-estate it occupies to help make the snapshot smaller. The subvi is attached, so take a look at it to see how large it really is (drag the box of the cluster down to see the rest of the contents). It's actually a standard LabVIEW image data control, the same type as used in the graphics format functions (which may not be included in LabVIEW 8.0?).
- You probably don't actually want this new image element cluster anyway! This is only one example of something to wire into a queue. What are you wiring into your queue functions? Presumably your image from the camera? You need to wire this into the subvi and not what I've created in this example.
- To generate the queue ref in and queue ref out control/indicator, you need to right click the queue reference wire in your existing code, and select Create -> Control. This will create something similar to what's in my subvi, but it will be specific to your queue element type. You need to cut and paste this new control into the subvi as your queue reference input. Hover the mouse over the block diagram icon in my example and you'll see it's a strict reference to a queue of image elements. Yours will match whatever element type you are using in your code.
- To create the queue ref out, just copy the queue ref in control on the front panel, right click the new copy and select Change to Indicator, and rename it as queue ref out.
- Right click the icon of the front panel, and select Show Connector. Wire the two queue refs to the top left and top right. Wire the new image element control to the second left hand input, and wire the error clusters to the bottom left and right.
- Save the vi somewhere.
- Drag the icon from the front panel to your existing code and it will be inserted as a subvi. You should then wire up the terminals as required
A lot of this is all very basic LabVIEW coding practice. I suspect you really need to get to grips with the LabVIEW coding style, for which there are many useful examples and tutorials included with the LabVIEW distribution. Creating subvis is one of the first things you'll learn. Just put a day aside to studying all this and it will all become so much easier.
