Re: [Foxgui-users] FOX contributions: "gauge" widget

[Hardy, S. <Ste...@di...>]

Dan,

forgive me if it's in the reference (which I haven't had time to look
at), but what is the PixFunc_f function supposed to do?

Maybe AA would not be *too* CPU-intensive for this simple widget, but
realistically I think it would require a backing image for the "scale",
which would then be practically constant unless resized.  Only the
pointers would need to be alpha-blended using some client-side tricks
like your code shows.

Another cheesy trick would be to render into a client-side image of 2 or
3 times the required size in both directions, then average (or maybe
convolve) into a smaller image.  This would be more like OpenGL style
texture mapping, but much simpler of course.

Regards,
SJH

PS: This is all very well, but actually the thing I like about FOX is
the blazing speed, and I don't want to give that up lightly just because
the widgets are a bit ugly.  A lot of the stuff I do really benefits
from having the CPU mostly available for the app logic and hardly
bothered by the user interface.


> -----Original Message-----
> From: fox...@li... [mailto:foxgui-users-
> bo...@li...] On Behalf Of Daniel Stine
> Sent: Friday, April 18, 2008 11:48 AM
> To: fox...@li...
> Subject: Re: [Foxgui-users] FOX contributions: "gauge" widget
> 
> Stephen,
> 
> I agree with Georg that AA will make the arbitrarily slanted lines
> smoother and scale down better.  As a side effect it will also make
> them a little thicker overall so you may not be able to fit as many
> minor divisions into the scale.
> 
> As you guessed antialiasing is simple to implement in OpenGL because
> it's built into the library.  However, OpenGL would make your widget
> much heavier than required.
> 
> Since I do most of my FOX development on Windows I've been through the
> M/S help documents extensively.
> The Windows GDI library does not have built-in support for AA that I
> have found.  It's not that hard to find line antialiasing code in
> various places online and roll your own function.
> 
> Here's a function that I've used.  I lifted it from either Paul
> Bourke, Anti-Grain Geometry, or Dr. Kotowski
> http://www.mini.pw.edu.pl/~kotowski/Grafika/RasterDrawing/Index.html,
> I can't remember, but it's not entirely my own work.
> 
> This is the Gupta-Sproull algorithm. The other one to search for is
> called Bresenham.
> 
> Regards,
> Dan
> 
> 
> //
> // Gupta-Sproull antialias
> //
> #define SWAP(Aa,Bb) { n = Aa; Aa = Bb; Bb = n; }
> void antialias(FXDCWindow *dcp, FXint x1, FXint y1, FXint x2, FXint
> y2, PixFunc_f pfunc)
> {
>     FXint n;
>     FXint u,u1,u2;
>     FXint v,v1,v2;
>     FXbool transpose = (abs(y2 - y1) > abs(x2 - x1));
>     if (transpose) {
>  u1 = y1; u2 = y2;
>  v1 = x1; v2 = x2;
>     }
>     else {
>  u1 = x1; u2 = x2;
>  v1 = y1; v2 = y2;
>     }
>     if (u1 > u2) {
>  SWAP(u1, u2)
>  SWAP(v1, v2)
>     }
>     FXint du = u2 - u1;
>     FXint dv = abs(v2 - v1);
>     FXint incrE = 2*dv;
>     FXint incrNE = 2*(dv - du);
>     FXint error = 2*dv - du;
>     FXint vstep = (v1 < v2) ? 1 : -1;
> 
>     FXint numer = 0; // numerator, v=0 for start pixel
>     FXdouble denom = 2.0*sqrt((FXdouble)du*du + dv*dv); // precomputed
> denominator
>     FXdouble two_du_over_denom = 2*du/denom; // precomputed constant
> 
>     v = v1;
>     for (u=u1; u<=u2; u++) {
>  color_pixel(dcp, u,v, fabs(numer/denom), pfunc, transpose);
>  for (n=1; color_pixel(dcp, u, v - vstep*n, fabs(n*two_du_over_denom +
> numer/denom), pfunc, transpose); n++);
>  for (n=1; color_pixel(dcp, u, v + vstep*n, fabs(n*two_du_over_denom -
> numer/denom), pfunc, transpose); n++);
>  if (error > 0) {
>     numer = error - du;
>     error += incrNE;
>     v += vstep;
>  }
>  else {
>     numer = error + du;
>     error += incrE;
>  }
>     }
> 
>     return;
> }
> 
> 
> FXbool color_pixel(FXDCWindow *dcp, FXint u, FXint v, FXdouble
> distance, PixFunc_f pfunc, FXbool reflect)
> {
>     FXdouble factor;
> 
>     if (distance < lineWidth/2.0) {
> 	factor = 1.0 - 2.0*distance/lineWidth;
> 	(this->*pfunc)(dcp, u,v, factor*255, reflect);
> 	return true;
>     }
> 
>     return false;
> }
> 
> 
> 
> > If anyone knows of a cheesy trick that might work for FXGauge then
> I'm
> > all ears...
> 
>
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