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[FT] Prefer downscaling bitmap glyphs to upscaling

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Say, you have bitmap strikes for sizes 50ppem and 100ppem.
To render at 60ppem, it's much better to downscale the 100ppem
bitmap than upscale 50ppem one.  Prefer downscaling.
This commit is contained in:
Behdad Esfahbod 2013-03-08 06:21:59 -05:00
parent 4f00d2344c
commit a8f1b456db
1 changed files with 12 additions and 3 deletions
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15
src/cairo-ft-font.c
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@ -739,6 +739,7 @@ _compute_transform (cairo_ft_font_transform_t *sf,
if (unscaled && (unscaled->face->face_flags & FT_FACE_FLAG_SCALABLE) == 0) {
double min_distance = DBL_MAX;
cairo_bool_t magnify = TRUE;
int i;
int best_i = 0;
double best_x_size = 0;
@ -747,10 +748,18 @@ _compute_transform (cairo_ft_font_transform_t *sf,
for (i = 0; i < unscaled->face->num_fixed_sizes; i++) {
double x_size = unscaled->face->available_sizes[i].y_ppem / 64.;
double y_size = unscaled->face->available_sizes[i].y_ppem / 64.;
double distance = fabs (y_size - y_scale);
double distance = y_size - y_scale;
if (distance <= min_distance) {
min_distance = distance;
/*
* distance is positive if current strike is larger than desired
* size, and negative if smaller.
*
* We like to prefer down-scaling to upscaling.
*/
if ((magnify && distance >= 0) || fabs (distance) <= min_distance) {
magnify = distance < 0;
min_distance = abs (distance);
best_i = i;
best_x_size = x_size;
best_y_size = y_size;