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calculate the fraction from the zoom ratio using continued fractions. This 

2004-01-11  Simon Budig  <simon@gimp.org>

	* app/display/gimpdisplayshell-scale.c: calculate the
	fraction from the zoom ratio using continued fractions.
	This prefers smaller numbers in numerator/denominator.

	Adresses bug #124073, but does not completely fix it,
	since scaling up/down does not always result in the same
	ratios.
This commit is contained in:
Simon Budig 2004-01-10 23:44:24 +00:00 committed by Simon Budig
parent 93ae08133b
commit f0cf80cc86
2 changed files with 53 additions and 47 deletions
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10
ChangeLog
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@ -1,3 +1,13 @@
2004-01-11 Simon Budig <simon@gimp.org>
* app/display/gimpdisplayshell-scale.c: calculate the
fraction from the zoom ratio using continued fractions.
This prefers smaller numbers in numerator/denominator.
Adresses bug #124073, but does not completely fix it,
since scaling up/down does not always result in the same
ratios.
2004-01-10 Ville Pätsi <drc@gimp.org>
* gimp.spec.in: Changed epoch to 2.

90
app/display/gimpdisplayshell-scale.c
View File

@ -105,66 +105,62 @@ gimp_display_shell_scale_calc_fraction (gdouble zoom_factor,
gint *scalesrc,
gint *scaledest)
{
gdouble zoom_delta;
gdouble min_zoom_delta = G_MAXFLOAT;
gint best_i = 0xFF;
gint i;
gint p0, p1, p2;
gint q0, q1, q2;
gdouble remainder, next_cf;
g_return_if_fail (scalesrc != NULL);
g_return_if_fail (scaledest != NULL);
if (zoom_factor < 1.0)
/* calculate the continued fraction for the desired zoom factor */
p0 = 1;
q0 = 0;
p1 = floor (zoom_factor);
q1 = 1;
remainder = zoom_factor - p1;
while (fabs (remainder) >= 0.0001 &&
fabs (((gdouble) p1 / q1) - zoom_factor) > 0.0001)
{
for (i = 0xFF; i > 0; i--)
{
*scalesrc = i;
*scaledest = floor ((gdouble) *scalesrc * zoom_factor);
remainder = 1.0 / remainder;
if (*scaledest < 0x1)
*scaledest = 0x1;
next_cf = floor (remainder);
zoom_delta = ABS ((gdouble) *scaledest / (gdouble) *scalesrc -
zoom_factor);
p2 = next_cf * p1 + p0;
q2 = next_cf * q1 + q0;
if (zoom_delta <= min_zoom_delta)
{
min_zoom_delta = zoom_delta;
best_i = i;
}
}
/* Numerator and Denominator are limited by 255 */
if (p2 > 255 || q2 > 255)
break;
*scalesrc = best_i;
*scaledest = floor ((gdouble) *scalesrc * zoom_factor);
/* remember the last two fractions */
p0 = p1;
p1 = p2;
q0 = q1;
q1 = q2;
if (*scaledest < 0x1)
*scaledest = 0x1;
remainder = remainder - next_cf;
}
else
zoom_factor = (gdouble) p1 / q1;
/* hard upper and lower bounds for zoom ratio */
if (zoom_factor > 255.0)
{
for (i = 0xFF; i > 0; i--)
{
*scaledest = i;
*scalesrc = ceil ((gdouble) *scaledest / zoom_factor);
if (*scalesrc < 0x1)
*scalesrc = 0x1;
zoom_delta = ABS ((gdouble) *scaledest / (gdouble) *scalesrc -
zoom_factor);
if (zoom_delta <= min_zoom_delta)
{
min_zoom_delta = zoom_delta;
best_i = i;
}
}
*scaledest = best_i;
*scalesrc = ceil ((gdouble) *scaledest / zoom_factor);
if (*scalesrc < 0x1)
*scalesrc = 0x1;
p1 = 255;
q1 = 1;
}
else if (zoom_factor < 1.0 / 255.0)
{
p1 = 1;
q1 = 255;
}
*scalesrc = q1;
*scaledest = p1;
}
void