nanogui: nanoX coordinate system
Subject:
RE: nanoX coordinate system
From:
Greg Haerr ####@####.####
Date:
10 May 1999 18:18:00 -0000
Message-Id: <01BE9ADF.5AD733B0.greg@censoft.com>
My comments follow... gh
On Monday, May 10, 1999 11:36 AM, Ben Pfaff ####@####.#### wrote:
> Greg Haerr ####@####.#### writes:
>
> Graphics coordinate systems typically come in one of two flavors:
>
> DrawLine(x1, y1, x2, y2); - draw a line from (x1, y1) to (x2, y2)
>
> Type 1 systems draw a line *including* (x2, y2)
> Type 2 systems draw a line *not including* the last point (x2, y2)
>
> In my experience, Type 2 systems are usually more convenient for
> geometric arithmetic; i.e., you only need to say `x2 - x1' to find a
> dimension, which results in fewer off-by-one adjustments.
>
I agree.
> One way to think of a type 2 system is that the points are between the
> gridlines rather than centered on the grid intersections.
Yep.
>
> For upper level api's there is a third type, that has width and height passed
> rather than using x2, y2. NanoX uses this, but I plan to change it. this goes
> for Ellipse specification as well.
>
> That's the way that X specifies rectangles, actually (width, height).
I kind of like the way that MSWindows specifies them, eg:
Ellipse(x1, y1, x2, y2);
The two points are the bounding box for the Ellipse. I plan on making
this change in internals to nanoX. We will want to keep the upper level API
very X-compliant. (I have sneaky plans to implement nanoWin - a small
windowing system that implements that Win32 API... This would run
on many small systems)
>
> My feeling is that type 2 systems are the way to go, because rectangles
> are described by two points in a bounding box, rather than width and height. Also,
> in 0-based coordinate systems, x2,y2 is the width and height, rather than having to
> calculate it. Ms-Windows gdi programming is easy because of this.
>
> Currently, nanoX uses the type 1 specification, and we need the flexibility of using
> drivers that are written to type 2.
>
> Ben: bogl currently aborts() when I try this. Check out BOGL_fillrect for details.
>
> When you try what? Do you mean I should look at a wrapper routine to
> see something you worked around?
Two things:
1. Uncomment the BOGL_clear() code in drivers/scr_bogl.c. This uses
my included bogl driver. It fails on an assert that I didn't have time to look at this morning.
2. Change the LIBBOGL line in the master makefile to use one of
your most recent bogl libaries. I would like to use unmodified bogl libraries.
Note there are two bugs:
1. recent bogl libraries don't use bogl_ncols anymore. I still use it.
2. bogl_text requres the yy parameter to be adjusted down by font->height.
This is because text 0,0 is at the upper left, *not* lower left as you have it. (see
drivers/bogl/bogl-cfb8.c for details)
Greg
>
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