Real world measurements...

[Paul_Boland]

Hi Folks.

I'm working on a program which will allow the user to print off a screenshot of what's on screen. The problem I'm having is, I need real world measurements. Specifically, I need millimeters to be millimeters. I did a search online about this and instantly came across a problem...

Different monitor sizes running at different resolutions means different pixles per inch! For example, on a monitor running at 1024 x 768 on a monitor 17" diagonal, there are 75pixels to the inch. Change the resolution and/or monitor size and the pixels per inch changes too. Umm ...!!

Now obviously there is a system out there that works. Desktop publishing programs such Microsoft Publisher can handle real world measurements on any size screen running at any resolution. But can MMF do this? Is there a way to get a real world measurement system working in MMF so if a user of a program draws a line 1mm long, 10mm long, 100mm long, etc., and they print it out, they get a printout of their lines 1mm long, 10mm long, 100mm long, etc....???

[Dines]

Is this what you mean:

I draw a box that's 500px wide. I grab a ruler, put it against my screen, and find that 500px on my screen appears, say 3 inches wide (it doesn't actually, but bear with me). I click print, and the printer draws my 500px box as a 3 inch box.

I then run my program using a different PC. That PC has a bigger screen. My 500px box now measures 4 inches wide on that screen. I print, and the printer draws a 4 inch box.

If that's what you want, then I'm afraid you're out of luck. There's currently no reliable way to get the screen's physical size. Windows' own GetDeviceCaps() function will let you get the size of the screen in Logical Inches, but these are woefully inaccurate, and depend on your screen settings as defined in the Windows Dialogs.

In other words, if I understand it correctly, then by changing the DPI in the Windows Display Settings dialogs, you can change what GetDeviceCaps() considers to be the size of a pixel on the screen - it bears no relation to physical dimensions.

Word is basically all vectors, so it can print to a device in inches and centimetres, but it can't display those measurements accurately on the screen. So in other words, if you make a 5 inch box on MS Word, zoom to 100% and get a ruler, your box will almost certainly NOT measure 5 inches. But it will when you print it. Another easy test is to open a document in Word, zoom to 100%, and place an A4 sheet of paper over your screen. On my screen, the A4 sheet is actually an inch wider than Word displays it.

EDIT:

If it's that important to your application, a simple setup dialog should be possible. You could ask the user to hold a piece of paper up to the screen or a ruler and just let them resize a box on the screen to match it. Then store the number of pixels / physical size in your app. That'll give you very accurate results.

[Paul_Boland]

Thanks for the detailed reply, appreciated. I'm not specifically looking for exact measurements on screen, but I do need them for printing. I want the user to be able to work in real world measurements so if they want a box 40mm in size, when they print they get a printed box 40mm in size. Given some of what you said, and some of my own testing, I don't think this is possible in MMF. But I think I've come up with a workaround for it, but it's ackward. Thanks again.