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Increase accuracy of IP instruction

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* src/sfnt.c (sfnt_interpret_ip): Avoid precision loss by
retrieving original positions from the unscaled outline,
whenever possible.
This commit is contained in:
Po Lu 2024-01-17 09:30:47 +08:00
parent f19f5604de
commit daec3e7b41
1 changed files with 83 additions and 3 deletions
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86
src/sfnt.c
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@ -9640,6 +9640,8 @@ sfnt_interpret_ip (struct sfnt_interpreter *interpreter)
sfnt_f26dot6 new_distance;
uint32_t p;
sfnt_f26dot6 x, y, original_x, original_y;
struct sfnt_interpreter_zone *zone;
bool scale;
/* First load both reference points. */
sfnt_address_zp0 (interpreter, interpreter->state.rp1,
@ -9649,6 +9651,57 @@ sfnt_interpret_ip (struct sfnt_interpreter *interpreter)
&rp2x, &rp2y, &rp2_original_x,
&rp2_original_y);
/* If RP1, RP2, and all arguments all fall within the glyph zone and
a simple glyph is loaded, replace their original coordinates as
loaded here with coordinates from the unscaled glyph outline. */
zone = interpreter->glyph_zone;
scale = false;
if (zone && zone->simple
&& interpreter->state.zp0
&& interpreter->state.zp1
&& interpreter->state.zp2)
{
p = interpreter->state.rp1;
/* If P is a phantom point... */
if (p >= zone->simple->number_of_points)
{
/* ...scale the phantom point to the size of the original
outline. */
rp1_original_x = sfnt_div_fixed (rp1_original_x,
interpreter->scale);
rp1_original_y = sfnt_div_fixed (rp1_original_y,
interpreter->scale);
}
else
{
rp1_original_x = zone->simple->x_coordinates[p];
rp1_original_y = zone->simple->y_coordinates[p];
}
p = interpreter->state.rp2;
/* If P is a phantom point... */
if (p >= zone->simple->number_of_points)
{
/* ...scale the phantom point to the size of the original
outline. */
rp2_original_x = sfnt_div_fixed (rp2_original_x,
interpreter->scale);
rp2_original_y = sfnt_div_fixed (rp2_original_y,
interpreter->scale);
}
else
{
rp2_original_x = zone->simple->x_coordinates[p];
rp2_original_y = zone->simple->y_coordinates[p];
}
scale = true;
}
/* Get the original distance between of RP1 and RP2 measured
relative to the dual projection vector. */
range = sfnt_dual_project_vector (interpreter,
@ -9657,6 +9710,9 @@ sfnt_interpret_ip (struct sfnt_interpreter *interpreter)
sfnt_sub (rp2_original_y,
rp1_original_y));
if (scale)
range = sfnt_mul_fixed_round (range, interpreter->scale);
/* Get the new distance. */
new_range = sfnt_dual_project_vector (interpreter,
sfnt_sub (rp2x, rp1x),
@ -9670,6 +9726,25 @@ sfnt_interpret_ip (struct sfnt_interpreter *interpreter)
sfnt_address_zp2 (interpreter, p, &x, &y, &original_x,
&original_y);
if (scale)
{
/* If P is a phantom point... */
if (p >= zone->simple->number_of_points)
{
/* ...scale the phantom point to the size of the original
outline. */
original_x = sfnt_div_fixed (original_x,
interpreter->scale);
original_y = sfnt_div_fixed (original_y,
interpreter->scale);
}
else
{
original_x = zone->simple->x_coordinates[p];
original_y = zone->simple->y_coordinates[p];
}
}
/* Now compute the old distance from this point to rp1. */
org_distance
= sfnt_dual_project_vector (interpreter,
@ -9678,6 +9753,10 @@ sfnt_interpret_ip (struct sfnt_interpreter *interpreter)
sfnt_sub (original_y,
rp1_original_y));
if (scale)
org_distance = sfnt_mul_fixed_round (org_distance,
interpreter->scale);
/* And the current distance from this point to rp1, so
how much to move can be determined. */
cur_distance
@ -11447,7 +11526,8 @@ sfnt_interpret_mirp (struct sfnt_interpreter *interpreter,
coordinate from the font designer's intentions, either exaggerating
or neutralizing the slant of the stem to which it belongs.
This behavior applies only to MDRP, which see. */
This behavior applies only to MDRP (which see), although a similar
strategy is also applied while interpreting IP instructions. */
static sfnt_f26dot6
sfnt_project_zp1_zp0_org (struct sfnt_interpreter *interpreter,
@ -20715,8 +20795,8 @@ main (int argc, char **argv)
return 1;
}
#define FANCY_PPEM 16
#define EASY_PPEM 16
#define FANCY_PPEM 14
#define EASY_PPEM 14
interpreter = NULL;
head = sfnt_read_head_table (fd, font);