On 16 Jan 2011, at 14:55, Lee Privett wrote: > Hey people, has anyone come across any articles or information that allows > the use of the line or circle command that draws to the screen accurately > accoding the known dot resolution? > > Let me explain > > Say you have a maximum screen of 1280w800h, and a window#1 of 1280x800x0x0 > > Using a SCALE command of 800,0,0 allows drawing a line from 0 to 768 that > reaches from the bottom to the top accurately but the x value is way off > screen drawing to 1280 > > I have my own formulae for an x multiplication factor that seems to work well > making squares appear square on the screen and circles appear circular on the > screen as well, but not being a mathematics person my formulae is not very > scientific and I have yet to check it on larger screens where any errors > would be magnified. > > It seems however to work on standard QL screen of 512x256 well. I was just > wondering before I explore any further if anyone else had writen anything on > it or if anyone had any comments?
As it happens I am just in the process of looking at this problem. The problem is twofold. First the pixels may not be square. Indeed they differ in shape between a Q40/60 and QPC2. Different sizes of Aurora give different shapes too. The second problem is that the graphics coordinates have a different effective size from pixels. I wanted to draw lines using graphics between two points defined by pixel positions. This is the reverse of trying to annotate diagrams drawn by the graphics commands. SCALE x,y,a,b allows that. To draw lines between two pixel positions is possible by setting SCALE h,0,0, where h is the height of the window in pixels. The graphics coordinates of pixel position x, y become x/1.35, h-y. This seems to work on Q60 and QPC2. Circles and squares on a Q60 are ellipses and oblongs on QPC2 and differing sizes of screen with Aurora. I found by trial and error values that made circles circular and oblongs square. I don't know of any other method. It depends on the shape of pixels and I don't know where that is defined. George _______________________________________________ QL-Users Mailing List http://www.q-v-d.demon.co.uk/smsqe.htm
