Initial support for \fax, \fay override tags

This adds support for the \fax and \fay override tags which can be used
for shearing the text horizontally and vertically. At the moment, this
works correctly on a per-glyph basis, however, the glyph positioning is
wrong, which is especially evident with \fay.

2 files changed, 33 insertions, 16 deletions

diff --git a/libass/ass_cache_template.c b/libass/ass_cache_template.c
index 11c7588..96b4752 100644
--- a/libass/ass_cache_template.c
+++ b/libass/ass_cache_template.c
@@ -69,6 +69,8 @@ START(bitmap, bipmap_hash_key_s)
     GENERIC(int, frx) // signed 16.16
     GENERIC(int, fry) // signed 16.16
     GENERIC(int, frz) // signed 16.16
+    GENERIC(int, fax) // signed 16.16
+    GENERIC(int, fay) // signed 16.16
     // shift vector that was added to glyph before applying rotation
     // = 0, if frx = fry = frx = 0
     // = (glyph base point) - (rotation origin), otherwise
diff --git a/libass/ass_render.c b/libass/ass_render.c
index 870623e..385821e 100644
--- a/libass/ass_render.c
+++ b/libass/ass_render.c
@@ -103,6 +103,7 @@ typedef struct glyph_info_s {
     double blur;                // gaussian blur
     double shadow;
     double frx, fry, frz;       // rotation
+    double fax, fay;            // text shearing
 
     bitmap_hash_key_t hash_key;
 } glyph_info_t;
@@ -135,6 +136,7 @@ typedef struct render_context_s {
     FT_Stroker stroker;
     int alignment;              // alignment overrides go here; if zero, style value will be used
     double frx, fry, frz;
+    double fax, fay;            // text shearing
     enum { EVENT_NORMAL,        // "normal" top-, sub- or mid- title
         EVENT_POSITIONED,       // happens after pos(,), margins are ignored
         EVENT_HSCROLL,          // "Banner" transition effect, text_width is unlimited
@@ -920,13 +922,17 @@ static char *parse_tag(ass_renderer_t *render_priv, char *p, double pwr)
         if (mystrtoi(&p, &val))
             mp_msg(MSGT_ASS, MSGL_V, "stub: \\yshad%d\n", val);
     } else if (mystrcmp(&p, "fax")) {
-        int val;
-        if (mystrtoi(&p, &val))
-            mp_msg(MSGT_ASS, MSGL_V, "stub: \\fax%d\n", val);
+        double val;
+        if (mystrtod(&p, &val))
+            render_priv->state.fax = val;
+        else
+            render_priv->state.fax = 0.;
     } else if (mystrcmp(&p, "fay")) {
-        int val;
-        if (mystrtoi(&p, &val))
-            mp_msg(MSGT_ASS, MSGL_V, "stub: \\fay%d\n", val);
+        double val;
+        if (mystrtod(&p, &val))
+            render_priv->state.fay = val;
+        else
+            render_priv->state.fay = 0.;
     } else if (mystrcmp(&p, "iclip")) {
         int x0, y0, x1, y1;
         int res = 1;
@@ -1536,6 +1542,7 @@ static void reset_render_context(ass_renderer_t *render_priv)
     render_priv->state.shadow = render_priv->state.style->Shadow;
     render_priv->state.frx = render_priv->state.fry = 0.;
     render_priv->state.frz = M_PI * render_priv->state.style->Angle / 180.;
+    render_priv->state.fax = render_priv->state.fay = 0.;
 
     // FIXME: does not reset unsupported attributes.
 }
@@ -1734,7 +1741,7 @@ get_outline_glyph(ass_renderer_t *render_priv, int symbol,
 
 static void transform_3d(FT_Vector shift, FT_Glyph * glyph,
                          FT_Glyph * glyph2, double frx, double fry,
-                         double frz);
+                         double frz, double fax, double fay);
 
 /**
  * \brief Get bitmaps for a glyph
@@ -1768,7 +1775,8 @@ get_bitmap_glyph(ass_renderer_t *render_priv, glyph_info_t *info)
             shift.y = int_to_d6(info->hash_key.shift_y);
             // apply rotation
             transform_3d(shift, &info->glyph, &info->outline_glyph,
-                         info->frx, info->fry, info->frz);
+                         info->frx, info->fry, info->frz, info->fax,
+                         info->fay);
 
             // render glyph
             error = glyph_to_bitmap(render_priv->synth_priv,
@@ -2101,7 +2109,7 @@ static void get_base_point(FT_BBox bbox, int alignment, int *bx, int *by)
  */
 static void
 transform_3d_points(FT_Vector shift, FT_Glyph glyph, double frx,
-                    double fry, double frz)
+                    double fry, double frz, double fax, double fay)
 {
     double sx = sin(frx);
     double sy = sin(fry);
@@ -2115,8 +2123,8 @@ transform_3d_points(FT_Vector shift, FT_Glyph glyph, double frx,
     int i;
 
     for (i = 0; i < outline->n_points; i++) {
-        x = p[i].x + shift.x;
-        y = p[i].y + shift.y;
+        x = (double) p[i].x + shift.x + (-fax * p[i].y);
+        y = (double) p[i].y + shift.y + (-fay * p[i].x);
         z = 0.;
 
         xx = x * cz + y * sz;
@@ -2152,16 +2160,16 @@ transform_3d_points(FT_Vector shift, FT_Glyph glyph, double frx,
  */
 static void
 transform_3d(FT_Vector shift, FT_Glyph * glyph, FT_Glyph * glyph2,
-             double frx, double fry, double frz)
+             double frx, double fry, double frz, double fax, double fay)
 {
     frx = -frx;
     frz = -frz;
-    if (frx != 0. || fry != 0. || frz != 0.) {
+    if (frx != 0. || fry != 0. || frz != 0. || fax != 0. || fay != 0.) {
         if (glyph && *glyph)
-            transform_3d_points(shift, *glyph, frx, fry, frz);
+            transform_3d_points(shift, *glyph, frx, fry, frz, fax, fay);
 
         if (glyph2 && *glyph2)
-            transform_3d_points(shift, *glyph2, frx, fry, frz);
+            transform_3d_points(shift, *glyph2, frx, fry, frz, fax, fay);
     }
 }
 
@@ -2301,6 +2309,8 @@ ass_render_event(ass_renderer_t *render_priv, ass_event_t *event,
         text_info->glyphs[text_info->length].frx = render_priv->state.frx;
         text_info->glyphs[text_info->length].fry = render_priv->state.fry;
         text_info->glyphs[text_info->length].frz = render_priv->state.frz;
+        text_info->glyphs[text_info->length].fax = render_priv->state.fax;
+        text_info->glyphs[text_info->length].fay = render_priv->state.fay;
         ass_font_get_asc_desc(render_priv->state.font, code,
                               &text_info->glyphs[text_info->length].asc,
                               &text_info->glyphs[text_info->length].desc);
@@ -2326,6 +2336,10 @@ ass_render_event(ass_renderer_t *render_priv, ass_event_t *event,
             render_priv->state.fry * 0xFFFF;
         text_info->glyphs[text_info->length].hash_key.frz =
             render_priv->state.frz * 0xFFFF;
+        text_info->glyphs[text_info->length].hash_key.fax =
+            render_priv->state.fax * 0xFFFF;
+        text_info->glyphs[text_info->length].hash_key.fay =
+            render_priv->state.fay * 0xFFFF;
         text_info->glyphs[text_info->length].hash_key.bold =
             render_priv->state.bold;
         text_info->glyphs[text_info->length].hash_key.italic =
@@ -2535,7 +2549,8 @@ ass_render_event(ass_renderer_t *render_priv, ass_event_t *event,
             glyph_info_t *info = text_info->glyphs + i;
 
             if (info->hash_key.frx || info->hash_key.fry
-                || info->hash_key.frz) {
+                || info->hash_key.frz || info->hash_key.fax
+                || info->hash_key.fay) {
                 info->hash_key.shift_x = info->pos.x + device_x - center.x;
                 info->hash_key.shift_y =
                     -(info->pos.y + device_y - center.y);