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faster, more accurate convergence for autofit

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better next guess, better final choice
This commit is contained in:
John Cupitt 2017-09-19 12:56:42 +01:00
parent 3cd0d5f161
commit f4151d6e5b
1 changed files with 77 additions and 36 deletions
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113
libvips/create/text.c
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@ -159,7 +159,7 @@ text_layout_new( PangoContext *context,
}
static int
text_get_extents( VipsText *text, VipsRect *extents )
vips_text_get_extents( VipsText *text, VipsRect *extents )
{
PangoRectangle logical_rect;
@ -180,7 +180,7 @@ text_get_extents( VipsText *text, VipsRect *extents )
extents->height = PANGO_PIXELS( logical_rect.height );
#ifdef DEBUG
printf( "text_get_extents: dpi = %d, "
printf( "vips_text_get_extents: dpi = %d, "
"left = %d, top = %d, width = %d, height = %d\n",
text->dpi,
extents->left, extents->top, extents->width, extents->height );
@ -189,76 +189,118 @@ text_get_extents( VipsText *text, VipsRect *extents )
return( 0 );
}
/* Compare two rects and return a number estimating their difference. 0 for
* the same, negative for first smaller, positive for first larger. One rect
* must enclose the other.
*/
static int
vips_text_rect_difference( VipsRect *a, VipsRect *b )
{
int w_diff = a->width - b->width;
int h_diff = a->height - b->height;
g_assert( vips_rect_includesrect( a, b ) ||
vips_rect_includesrect( b, a ) );
/* We need the difference closest to zero.
*/
if( vips_rect_includesrect( a, b ) )
/* So w and h diff must both be positive. We want the smaller
* one.
*/
return( VIPS_MIN( w_diff, h_diff ) );
else
/* Both negative.
*/
return( VIPS_MAX( w_diff, h_diff ) );
}
/* Adjust text->dpi to try to fit to the bounding box.
*/
static int
vips_text_autofit( VipsText *text )
{
VipsRect target;
VipsRect previous_target;
VipsRect extents;
VipsRect previous_extents;
int previous_dpi;
int lower;
int upper;
int difference;
int previous_difference;
int lower_dpi;
int upper_dpi;
int lower_difference;
int upper_difference;
/* First, repeatedly double or halve dpi until we pass the correct
* value. This will give us a lower and upper bound.
*/
target.width = text->width;
target.height = text->height;
previous_dpi = -1;
previous_dpi = text->dpi;
previous_difference = -1;
for(;;) {
if( text_get_extents( text, &extents ) )
if( vips_text_get_extents( text, &extents ) )
return( -1 );
target.left = extents.left;
target.top = extents.top;
difference = vips_text_rect_difference( &extents, &target );
if( previous_dpi == -1 ) {
previous_dpi = text->dpi;
previous_extents = extents;
previous_target = target;
}
if( previous_difference == -1 )
previous_difference = difference;
/* Too small last time, still too small.
*/
if( vips_rect_includesrect( &target, &extents ) &&
vips_rect_includesrect( &previous_target,
&previous_extents ) )
if( difference < 0 &&
previous_difference < 0 )
text->dpi *= 2;
/* Too big last time, still too big.
*/
else if( vips_rect_includesrect( &extents, &target ) &&
vips_rect_includesrect( &previous_extents,
&previous_target ) )
else if( difference > 0 &&
previous_difference > 0 )
text->dpi /= 2;
/* We now straddle the target!
/* We now straddle the target! Or both zero.
*/
else
break;
}
lower = VIPS_MIN( text->dpi, previous_dpi );
upper = VIPS_MAX( text->dpi, previous_dpi );
lower_dpi = VIPS_MIN( text->dpi, previous_dpi );
lower_difference = VIPS_MIN( difference, previous_difference );
upper_dpi = VIPS_MAX( text->dpi, previous_dpi );
upper_difference = VIPS_MAX( difference, previous_difference );
/* Refine lower and upper until they are almost touching.
/* Refine lower and upper until they are almost touching, or until we
* fit exactly.
*/
while( upper - lower > 2 ) {
text->dpi = (upper + lower) / 2;
if( text_get_extents( text, &extents ) )
while( upper_dpi - lower_dpi > 2 &&
lower_difference < 0 &&
upper_difference > 0 ) {
int total_difference = upper_difference - lower_difference;
double x = (double) -lower_difference / total_difference;
int guess_dpi = (upper_dpi - lower_dpi) * x + lower_dpi;
text->dpi = guess_dpi;
if( vips_text_get_extents( text, &extents ) )
return( -1 );
target.left = extents.left;
target.top = extents.top;
if( vips_rect_includesrect( &target, &extents ) )
lower = text->dpi;
else
upper = text->dpi;
difference = vips_text_rect_difference( &extents, &target );
if( difference < 0 ) {
lower_dpi = guess_dpi;
lower_difference = difference;
}
else {
upper_dpi = guess_dpi;
upper_difference = difference;
}
}
text->dpi = lower;
if( upper_difference == 0 )
text->dpi = upper_dpi;
else
text->dpi = lower_dpi;
return( 0 );
}
@ -291,12 +333,11 @@ vips_text_build( VipsObject *object )
* we get a fit.
*/
if( vips_object_argument_isset( object, "height" ) &&
!vips_object_argument_isset( object, "dpi" ) ) {
if( vips_text_autofit( text ) )
return( -1 );
}
!vips_object_argument_isset( object, "dpi" ) &&
vips_text_autofit( text ) )
return( -1 );
if( text_get_extents( text, &extents ) )
if( vips_text_get_extents( text, &extents ) )
return( -1 );
/* Can happen for "", for example.