harrow@exodus.dec.com (Jeff Harrow, NCSE LKG1-3/F16 DTN=226-7445) (08/18/86)
Having received such good advice from my last question about rubber-band lines, I now have another: Given that I have a random line going from StartPt to EndPt (any orientation), what is a good way to create a rectangular Region around it, perhaps 2 pixels out from the line (ie a Region which encloses the line but is slightly larger than the line itself, to make for easier mouse capture). (My problem is not in actually creating the Region, but making it come out in the shape that I want around the line...) My initial simplistic attempt at this (drawing a rectangle around it expanded by the magic "2") works fine for vertical lines, but the region is less and less rectangular, and less and less over the ends of the line (ok in the center) as the line approaches horizontal. (Something tells me that I wish I'd paid more attention to Trig...) Anyway, any ideas on a generalized algorithm? (This doesn't belong here, but boy, is Lightspeed PASCAL **GREAT**!) Jeff
sdh@joevax.UUCP (The Doctor) (08/19/86)
> Given that I have a random line going from StartPt to EndPt (any > orientation), what is a good way to create a rectangular Region > around it, perhaps 2 pixels out from the line (ie a Region which > encloses the line but is slightly larger than the line itself, to > make for easier mouse capture). (My problem is not in actually > creating the Region, but making it come out in the shape that I > want around the line...) > I haven't actually tried this, but you might want to try this routine /* this is for a c system */ surround_line(x1, y1, x2, y2, region) int x1, y1, x2, y3; RgnHandle region; /* this should do it. Note that this routine doesn't define the region * itself. You must do that with a call to NewRgn() before trying to * manipulate the contents. */ { Rect temprect; /* You may wish to set the rectangle differently than I do. * This case allows for what may be "improper" rectangles, that is , those * whose bottom is above their top, and left before there right. * it may be neccessary to sort the points accordingly, ie, if x1 is greater * than x2, swap them, and if y1 is greater than y2, swap them. This will * generate an equivalent rectangle, but not the specific one. * If a slash is a diagonal line, \ and / could be fit in the same * rectangle, but the routine generates spceific ones, not generalizations. */ SetRect(&temprect, x1, y1, x2, y2); InsetRect(&temprect, -2, -2); /* don't like the magic numbers */ RectRgn(region, &temprect); } Hope this helps. Steve Hawley
seth@hera.cs.ucla.edu (Seth Goldman) (08/20/86)
From reading IM, I would expect the proper way to create a
rectangular region given 2 endpoints would be to use
Pt2Rect (I-175) followed by a call to RectRgn (I-183).
You probably want to call InsetRect inbetween with an
offset of -2 in both directions.
Seth Goldman
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