Re: pngcairo: suggestion for additional option

[Allin C. <cot...@wf...>]

On Thu, 22 Nov 2007, Ethan A Merritt wrote:

> On Thursday 22 November 2007 08:19, Allin Cottrell wrote:
> > 
> > I'm attaching a small patch to eval.c that implements 
> > GPVAL_GRAPH_XMIN, GPVAL_GRAPH_XMAX, GPVAL_GRAPH_YMIN and 
> > GPVAL_GRAPH_YMAX. In the context of bitmapped output, these values 
> > should represent the pixel coordinates of the actual graph area.
> > 
> > Those more familiar than I with the gnuplot architecture will no 
> > doubt be able to see if there's a better way of doing this.
> 
> >--- eval.c.orig	2007-11-22 10:16:05.000000000 -0500
> >+++ eval.c	2007-11-22 11:05:46.000000000 -0500
> >@@ -733,6 +733,39 @@
> >     Gstring(&v->udv_value, gp_strdup(stringvalue));
> > }
> > 
> >+static void update_plot_bounds (void)
> >+{
> >+    int xl = plot_bounds.xleft;
> >+    int xr = plot_bounds.xright;
> >+    int yb = plot_bounds.ybot;
> >+    int yt = plot_bounds.ytop;
> 
> I think that has to be 
> 
>     unsigned int xl, xr, yb, yt;
>     struct position bottom_left = {graph, graph, graph, 0., 0., 0.};
>     struct position upper_right = {graph, graph, graph, 1., 1., 1.};
> 
>     map_position(&bottom_left, &xl, &yb, "");
>     map_position(&upper_right, &xr, &yt, "");

OK, I'll take your word for that!

> >+    if (term != NULL && !strcmp(term->name, "pngcairo")) {
> >+        /* convert to pixels */
> >+	xl /= 20;
> >+	xr /= 20;
> >+	yb /= 20;
> >+	yt /= 20;
> 
> Where did the magic number 20 come from?

The cairo code seems to deal in units of 1/20 of a pixel.  Note 
that in mouse.c we have, e.g.:

  mv_mouse_x = term->xmax / 20;

However, if something like the above assignment to 
GPVAL_GRAPH_XMIN et al is acceptable, I'd be happy even if no 
conversion to pixels is done -- that is, if the numbers are just 
whatever comes out of map_position().

Allin Cottrell