Adjust shearing behavior to match VSFilter

Make horizontal shearing (\fax) shear from top to bottom of a glyph;
scale shearing factors with horizontal and vertical scaling factors.
This makes the shearing operations similar to VSFilter, except for
\fay in some cases, but this is not unexpected.  Vertical shearing
is implemented different on purpose.

1 files changed, 15 insertions, 9 deletions

diff --git a/libass/ass_render.c b/libass/ass_render.c
index 0b66e56..253d409 100644
--- a/libass/ass_render.c
+++ b/libass/ass_render.c
@@ -2080,7 +2080,8 @@ get_outline_glyph(ASS_Renderer *render_priv, int symbol, GlyphInfo *info,
 
 static void transform_3d(FT_Vector shift, FT_Glyph *glyph,
                          FT_Glyph *glyph2, double frx, double fry,
-                         double frz, double fax, double fay, double scale);
+                         double frz, double fax, double fay, double scale,
+                         int yshift);
 
 /**
  * \brief Get bitmaps for a glyph
@@ -2106,15 +2107,19 @@ get_bitmap_glyph(ASS_Renderer *render_priv, GlyphInfo *info)
         FT_Vector shift;
         BitmapHashValue hash_val;
         int error;
+        double fax_scaled, fay_scaled;
         info->bm = info->bm_o = info->bm_s = 0;
         if (info->glyph && info->symbol != '\n' && info->symbol != 0) {
             // calculating rotation shift vector (from rotation origin to the glyph basepoint)
             shift.x = info->hash_key.shift_x;
             shift.y = info->hash_key.shift_y;
+            fax_scaled = info->fax * render_priv->font_scale_x *
+                         render_priv->state.scale_x;
+            fay_scaled = info->fay * render_priv->state.scale_y;
             // apply rotation
             transform_3d(shift, &info->glyph, &info->outline_glyph,
-                         info->frx, info->fry, info->frz, info->fax,
-                         info->fay, render_priv->font_scale);
+                         info->frx, info->fry, info->frz, fax_scaled,
+                         fay_scaled, render_priv->font_scale, info->asc);
 
             // subpixel shift
             if (info->glyph)
@@ -2474,7 +2479,8 @@ static void get_base_point(DBBox *bbox, int alignment, double *bx, double *by)
  */
 static void
 transform_3d_points(FT_Vector shift, FT_Glyph glyph, double frx, double fry,
-                    double frz, double fax, double fay, double scale)
+                    double frz, double fax, double fay, double scale,
+                    int yshift)
 {
     double sx = sin(frx);
     double sy = sin(fry);
@@ -2489,7 +2495,7 @@ transform_3d_points(FT_Vector shift, FT_Glyph glyph, double frx, double fry,
 
     dist = 20000 * scale;
     for (i = 0; i < outline->n_points; i++) {
-        x = (double) p[i].x + shift.x + (-fax * p[i].y);
+        x = (double) p[i].x + shift.x + (fax * (yshift - p[i].y));
         y = (double) p[i].y + shift.y + (-fay * p[i].x);
         z = 0.;
 
@@ -2527,18 +2533,18 @@ transform_3d_points(FT_Vector shift, FT_Glyph glyph, double frx, double fry,
 static void
 transform_3d(FT_Vector shift, FT_Glyph *glyph, FT_Glyph *glyph2,
              double frx, double fry, double frz, double fax, double fay,
-             double scale)
+             double scale, int yshift)
 {
     frx = -frx;
     frz = -frz;
     if (frx != 0. || fry != 0. || frz != 0. || fax != 0. || fay != 0.) {
         if (glyph && *glyph)
             transform_3d_points(shift, *glyph, frx, fry, frz,
-                                fax, fay, scale);
+                                fax, fay, scale, yshift);
 
         if (glyph2 && *glyph2)
             transform_3d_points(shift, *glyph2, frx, fry, frz,
-                                fax, fay, scale);
+                                fax, fay, scale, yshift);
     }
 }
 
@@ -2661,7 +2667,7 @@ ass_render_event(ASS_Renderer *render_priv, ASS_Event *event,
         pen.x += double_to_d6(render_priv->state.hspacing *
                               render_priv->font_scale);
         pen.y += text_info->glyphs[text_info->length].advance.y;
-        pen.y += render_priv->state.fay *
+        pen.y += (render_priv->state.fay * render_priv->state.scale_y) *
                  text_info->glyphs[text_info->length].advance.x;
 
         previous = code;