Let me explain this in more detail for those who might find my bug report confusing:
RTC has a usable "canvas" of 640x400 pixels which looks like this:
But RTC never runs in that resolution unless you tell it to, it actually runs in the very common, standard PC resolution of 640x480. So RTC compensates by placing it's canvas 40 pixels down the screen at 0,40, a bit like wide-screen:
This means that the origin for RTC coordinates is at 0,40 on a 640x480 display, but internally RTC treats this as 0,0.
It's possible to put a big bitmap in the background that extends BEYOND the 640x400 RTC canvas and to use the extra 80 pixels of wasted space in a 640x480 display.
You do this by setting the origin point of any 640x480 bitmap to start at 0,-40. So we're saying to RTC "Place this image 40 pixels further up the screen from where your normal 0,0 point is". This means our images appear at the TRUE 0,0 point on a 640x480 display.
If you use this method to place a larger 640x480 image on screens like the Main Menu or Plot Screens, you usually also have the option to place other images over the top -- buttons, etc.
Images overlayed in this way take their x,y coordinates from RTCs internal canvas, NOT the background image. So when you position overlayed buttons, if you put one at 0,0 it would actually appear at 0,40 on a 640x480 display. You have to remember to add 40 to all your Y axis values when doing this kind of overlay work.
But the Utility screen is different. You can place your 640x480 background image where you like and all the other overlaid items use the top left corner of this image as their 0,0 origin point.
This is completely inconsistent with what the other screens do, but in fact is much more logical.
(Sorry for the long explanation, I just wanted to get this all down for anyone who might not understand what's going on.)
So, questions:
1) Why is RTC doing this in different ways?
2) Can you make it consistent?
3) Better still, can't you just overhaul all of this so everything starts at true 0,0 on a 640x480 display?
As an aside, I'm kinda confused why you chose the default resolution of RTC to be 640x400.
I can see that it's double the original NTSC Atari ST resolution of 320x200, but weren't you an Amiga baby living in England?
PAL Amigas ran at 320x256... The closest PC equivalent would be 320x240 so would it not have made more sense to simply double up to 640x480 right from the start, surely? Why did you choose the NTSC resolution?
Sorry to sound critical -- I'm just rather bemused by these design decisions which don't really seem to make a lot of sense and make editing RTC much harder than it should be