C# Load Bitmap into PictureBox - slow and blocks UI .. any alternatives?

Question

I am loading 640x480 Bitmaps into a picture box one after the other. When I do that my UI gets blocked. For example, if I was typing something in a text box which is on the same form where my picture box is, I would not be able to see the key that pressed right away, because the bitmap loading makes the UI very slow .. How would one handle that ? is there any way around it ? Any sample code would be great.

Thanks

Answer 1

Use background worker so the gui is not freezed (async invoke the image display). http://www.dreamincode.net/forums/topic/112547-using-the-backgroundworker-in-c%23/

Your second request is a bit more tricky, I guess short answer would be not to rely on gdi+ if that's what you are doing be cause it's known to be slow. How exactly do you load the image into the imagebox?

Answer 2

A Picturebox is actually a fairly 'heavy' control in what it provides; it may not be the appropriate thing to use here. You might consider a much simpler container control, or drawing on the surface of the form itself.

If you want to consider BackgroundWorker or any other threaded technique here, keep in mind that the drawing itself must happen on the UI thread; there's no way around that.

If the loading of the images from disk is the source of the latency, you might consider loading the images into an in-memory bitmap on another thread, then signaling somehow to indicate that a new item is ready to be drawn. You would then invalidate the drawing surface, and add the new item as appropriate.

Also; if you are doing any scaling to the images, doing this in the background thread would be appropriate - that way, the drawing code itself only needs to draw an unscaled rect; Using the GDI+ DrawUnscaled functionality to copy a bitmap to an area of the exact same size is actually quite fast.

---

To get into anything more specific, like actual code, I would want to see code for how you are doing it now. I'm not even sure you are 'drawing' the images in the first place, rather than simply setting Picture / Image properties.