On 16/01/2011 15:39, gdgqler wrote:
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
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From memory, my program should take account of the different shape of
pixels....
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Rich Mellor
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