Implement drawing mode (\p)

Finally implement the drawing mode, which allows drawing of custom
vector graphics.  Drawings are intercepted in ass_render_event; a hash
of the drawing string is generated which is then used for looking
up drawings and bitmaps of drawings in the cache.  The drawings
itself are "fake" glyphs.  They are created by parsing the simple
drawing description language, evaluating the curves described (lines,
cubic beziers and/or a special kind of b-splines) and creating vector
outlines.  Afterwards, these drawings are (with a few exceptions, e.g.
ascender/descender) exactly handled like regular glyphs.

Support for vector clippings is still missing, but otherwise the
implementation should be complete and compatible with VSFilter.

The libass integration of the drawing parsing/processing code is still a
bit sketchy and should be refactored.

History:
WIP: Drawing mode infrastructure
WIP: Drawing tokenizer
WIP: Parse drawing tokens, call evaluators
WIP: Bezier/b-spline evaluator
WIP: Final pieces for the drawing mode
WIP: Heavy modifications to the drawing parser/tokenizer
WIP: Dynamic outline memory allocation
WIP: Drawing position fixes
WIP: more drawing position fixup (similar to VSFilter now)
WIP: Lots of cleanup and fixes for drawings.
WIP: Drawing mode integration into ass_render_event

8 files changed, 694 insertions, 68 deletions

diff --git a/libass/Makefile.am b/libass/Makefile.am
index ccdeebc..81b8b96 100644
--- a/libass/Makefile.am
+++ b/libass/Makefile.am
@@ -6,7 +6,8 @@ lib_LTLIBRARIES = libass.la
 libass_la_SOURCES = ass.c ass_cache.c ass_font.c ass_fontconfig.c ass_render.c \
                     ass_utils.c ass_bitmap.c ass_library.c ass_bitmap.h \
                     ass_cache.h ass_fontconfig.h ass_font.h ass.h \
-                    ass_library.h ass_types.h ass_utils.h help_mp.h
+                    ass_library.h ass_types.h ass_utils.h ass_drawing.c \
+                    ass_drawing.h help_mp.h
 libass_la_LDFLAGS = -version-info $(LIBASS_LT_CURRENT):$(LIBASS_LT_REVISION):$(LIBASS_LT_AGE)
 libass_la_LDFLAGS += -export-symbols $(srcdir)/libass.sym
 
diff --git a/libass/ass_cache.c b/libass/ass_cache.c
index 04b3acb..fc70b0d 100644
--- a/libass/ass_cache.c
+++ b/libass/ass_cache.c
@@ -34,33 +34,6 @@
 #include "ass_bitmap.h"
 #include "ass_cache.h"
 
-
-#define FNV1_32A_INIT (unsigned)0x811c9dc5
-
-static inline unsigned fnv_32a_buf(void *buf, size_t len, unsigned hval)
-{
-    unsigned char *bp = buf;
-    unsigned char *be = bp + len;
-    while (bp < be) {
-        hval ^= (unsigned) *bp++;
-        hval +=
-            (hval << 1) + (hval << 4) + (hval << 7) + (hval << 8) +
-            (hval << 24);
-    }
-    return hval;
-}
-static inline unsigned fnv_32a_str(char *str, unsigned hval)
-{
-    unsigned char *s = (unsigned char *) str;
-    while (*s) {
-        hval ^= (unsigned) *s++;
-        hval +=
-            (hval << 1) + (hval << 4) + (hval << 7) + (hval << 8) +
-            (hval << 24);
-    }
-    return hval;
-}
-
 static unsigned hashmap_hash(void *buf, size_t len)
 {
     return fnv_32a_buf(buf, len, FNV1_32A_INIT);
diff --git a/libass/ass_cache.h b/libass/ass_cache.h
index c1d25b2..d8de97a 100644
--- a/libass/ass_cache.h
+++ b/libass/ass_cache.h
@@ -102,6 +102,7 @@ typedef struct glyph_hash_val_s {
     FT_Glyph outline_glyph;
     FT_BBox bbox_scaled;        // bbox after scaling, but before rotation
     FT_Vector advance;          // 26.6, advance distance to the next bitmap in line
+    int asc, desc;              // ascender/descender of a drawing
 } glyph_hash_val_t;
 
 hashmap_t *ass_glyph_cache_init(void);
diff --git a/libass/ass_cache_template.c b/libass/ass_cache_template.c
index dd9adbd..bccb6db 100644
--- a/libass/ass_cache_template.c
+++ b/libass/ass_cache_template.c
@@ -78,6 +78,7 @@ START(bitmap, bipmap_hash_key_s)
     GENERIC(int, shift_y)
     FTVECTOR(advance) // subpixel shift vector
     FTVECTOR(shadow_offset) // shadow subpixel shift
+    GENERIC(unsigned, drawing_hash) // hashcode of a drawing
 END(bitmap_hash_key_t)
 
 // describes an outline glyph
@@ -91,6 +92,7 @@ START(glyph, glyph_hash_key_s)
     GENERIC(unsigned, scale_y) // 16.16
     FTVECTOR(advance) // subpixel shift vector
     FTVECTOR(outline) // border width, 16.16
+    GENERIC(unsigned, drawing_hash) // hashcode of a drawing
 END(glyph_hash_key_t)
 
 // Cache for composited bitmaps
diff --git a/libass/ass_drawing.c b/libass/ass_drawing.c
new file mode 100644
index 0000000..30d742f
--- /dev/null
+++ b/libass/ass_drawing.c
@@ -0,0 +1,477 @@
+/*
+ * Copyright (C) 2009 Grigori Goronzy <greg@geekmind.org>
+ *
+ * This file is part of libass.
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <ft2build.h>
+#include FT_GLYPH_H
+#include FT_OUTLINE_H
+#include FT_BBOX_H
+#include <math.h>
+
+#include "ass_utils.h"
+#include "ass_font.h"
+#include "ass_drawing.h"
+
+#define CURVE_ACCURACY 64.0
+#define GLYPH_INITIAL_POINTS 100
+#define GLYPH_INITIAL_CONTOURS 5
+
+/*
+ * \brief Get and prepare a FreeType glyph
+ */
+static void drawing_make_glyph(ass_drawing_t *drawing, void *fontconfig_priv,
+                               ass_font_t *font, ass_hinting_t hint)
+{
+    FT_OutlineGlyph glyph;
+
+    // This is hacky...
+    glyph = (FT_OutlineGlyph) ass_font_get_glyph(fontconfig_priv, font,
+                                                 (uint32_t) ' ', hint);
+
+    FT_Outline_Done(drawing->ftlibrary, &glyph->outline);
+    FT_Outline_New(drawing->ftlibrary, GLYPH_INITIAL_POINTS,
+                   GLYPH_INITIAL_CONTOURS, &glyph->outline);
+
+    glyph->outline.n_contours = 0;
+    glyph->outline.n_points = 0;
+    glyph->root.advance.x = glyph->root.advance.y = 0;
+    drawing->glyph = glyph;
+}
+
+/*
+ * \brief Add a single point to a contour.
+ */
+static inline void drawing_add_point(ass_drawing_t *drawing,
+                                     FT_Vector *point)
+{
+    FT_Outline *ol = &drawing->glyph->outline;
+
+    if (ol->n_points >= drawing->max_points) {
+        drawing->max_points *= 2;
+        ol->points = realloc(ol->points, sizeof(FT_Vector) *
+                             drawing->max_points);
+        ol->tags = realloc(ol->tags, drawing->max_points);
+    }
+
+    ol->points[ol->n_points].x = point->x;
+    ol->points[ol->n_points].y = point->y;
+    ol->tags[ol->n_points] = 1;
+    ol->n_points++;
+}
+
+/*
+ * \brief Close a contour and check glyph size overflow.
+ */
+static inline void drawing_close_shape(ass_drawing_t *drawing)
+{
+    FT_Outline *ol = &drawing->glyph->outline;
+
+    if (ol->n_contours >= drawing->max_contours) {
+        drawing->max_contours *= 2;
+        ol->contours = realloc(ol->contours, sizeof(short) *
+                               drawing->max_contours);
+    }
+
+    ol->contours[ol->n_contours] = ol->n_points - 1;
+    ol->n_contours++;
+}
+
+/*
+ * \brief Prepare drawing for parsing.  This just sets a few parameters.
+ */
+static void drawing_prepare(ass_drawing_t *drawing)
+{
+    // Scaling parameters
+    drawing->point_scale_x = drawing->scale_x *
+                             64.0 / (1 << (drawing->scale - 1));
+    drawing->point_scale_y = drawing->scale_y *
+                             64.0 / (1 << (drawing->scale - 1));
+}
+
+/*
+ * \brief Finish a drawing.  This only sets the horizontal advance according
+ * to the glyph's bbox at the moment.
+ */
+static void drawing_finish(ass_drawing_t *drawing)
+{
+    int i, offset;
+    FT_BBox bbox;
+    FT_Outline *ol = &drawing->glyph->outline;
+
+    // Close the last contour
+    drawing_close_shape(drawing);
+
+#if 0
+    // Dump points
+    for (i = 0; i < ol->n_points; i++) {
+        printf("point (%d, %d)\n", (int) ol->points[i].x,
+               (int) ol->points[i].y);
+    }
+
+    // Dump contours
+    for (i = 0; i < ol->n_contours; i++)
+        printf("contour %d\n", ol->contours[i]);
+#endif
+
+    FT_Outline_Get_CBox(&drawing->glyph->outline, &bbox);
+    drawing->glyph->root.advance.x = d6_to_d16(bbox.xMax - bbox.xMin);
+
+    drawing->desc = double_to_d6(-drawing->pbo * drawing->scale_y);
+    drawing->asc = bbox.yMax - bbox.yMin + drawing->desc;
+
+    // Place it onto the baseline
+    offset = (bbox.yMax - bbox.yMin) + double_to_d6(-drawing->pbo *
+                                                    drawing->scale_y);
+    for (i = 0; i < ol->n_points; i++)
+        ol->points[i].y += offset;
+}
+
+/*
+ * \brief Check whether a number of items on the list is available
+ */
+static int token_check_values(ass_drawing_token_t *token, int i, int type)
+{
+    int j;
+    for (j = 0; j < i; j++) {
+        if (!token || token->type != type) return 0;
+        token = token->next;
+    }
+
+    return 1;
+}
+
+/*
+ * \brief Tokenize a drawing string into a list of ass_drawing_token_t
+ * This also expands points for closing b-splines
+ */
+static ass_drawing_token_t *drawing_tokenize(char *str)
+{
+    char *p = str;
+    int i, val, type = -1, is_set = 0;
+    FT_Vector point = {0, 0};
+
+    ass_drawing_token_t *root = NULL, *tail = NULL, *spline_start = NULL;
+
+    while (*p) {
+        if (*p == 'c' && spline_start) {
+            // Close b-splines: add the first three points of the b-spline
+            // back to the end
+            if (token_check_values(spline_start->next, 2, TOKEN_B_SPLINE)) {
+                for (i = 0; i < 3; i++) {
+                    tail->next = calloc(1, sizeof(ass_drawing_token_t));
+                    tail->next->prev = tail;
+                    tail = tail->next;
+                    tail->type = TOKEN_B_SPLINE;
+                    tail->point = spline_start->point;
+                    spline_start = spline_start->next;
+                }
+                spline_start = NULL;
+            }
+        } else if (!is_set && mystrtoi(&p, &val)) {
+            point.x = val;
+            is_set = 1;
+            p--;
+        } else if (is_set == 1 && mystrtoi(&p, &val)) {
+            point.y = val;
+            is_set = 2;
+            p--;
+        } else if (*p == 'm')
+            type = TOKEN_MOVE;
+        else if (*p == 'n')
+            type = TOKEN_MOVE_NC;
+        else if (*p == 'l')
+            type = TOKEN_LINE;
+        else if (*p == 'b')
+            type = TOKEN_CUBIC_BEZIER;
+        else if (*p == 'q')
+            type = TOKEN_CONIC_BEZIER;
+        else if (*p == 's')
+            type = TOKEN_B_SPLINE;
+        // We're simply ignoring TOKEN_EXTEND_B_SPLINE here.
+        // This is not harmful at all, since it can be ommitted with
+        // similar result (the spline is extended anyway).
+
+        if (type != -1 && is_set == 2) {
+            if (root) {
+                tail->next = calloc(1, sizeof(ass_drawing_token_t));
+                tail->next->prev = tail;
+                tail = tail->next;
+            } else
+                root = tail = calloc(1, sizeof(ass_drawing_token_t));
+            tail->type = type;
+            tail->point = point;
+            is_set = 0;
+            if (type == TOKEN_B_SPLINE && !spline_start)
+                spline_start = tail->prev;
+        }
+        p++;
+    }
+
+#if 0
+    // Check tokens
+    ass_drawing_token_t *t = root;
+    while(t) {
+        printf("token %d point (%d, %d)\n", t->type, t->point.x, t->point.y);
+        t = t->next;
+    }
+#endif
+
+    return root;
+}
+
+/*
+ * \brief Free a list of tokens
+ */
+static void drawing_free_tokens(ass_drawing_token_t *token)
+{
+    while (token) {
+        ass_drawing_token_t *at = token;
+        token = token->next;
+        free(at);
+    }
+}
+
+/*
+ * \brief Translate and scale a point coordinate according to baseline
+ * offset and scale.
+ */
+static inline void translate_point(ass_drawing_t *drawing, FT_Vector *point)
+{
+    point->x = drawing->point_scale_x * point->x;
+    point->y = drawing->point_scale_y * -point->y;
+}
+
+/*
+ * \brief Evaluate a curve into lines
+ * This curve evaluator is also used in VSFilter (RTS.cpp); it's a simple
+ * implementation of the De Casteljau algorithm.
+ */
+static void drawing_evaluate_curve(ass_drawing_t *drawing,
+                                   ass_drawing_token_t *token, char spline,
+                                   int started)
+{
+    double cx3, cx2, cx1, cx0, cy3, cy2, cy1, cy0;
+    double t, h, max_accel, max_accel1, max_accel2;
+    FT_Vector cur = {0, 0};
+
+    cur = token->point;
+    translate_point(drawing, &cur);
+    int x0 = cur.x;
+    int y0 = cur.y;
+    token = token->next;
+    cur = token->point;
+    translate_point(drawing, &cur);
+    int x1 = cur.x;
+    int y1 = cur.y;
+    token = token->next;
+    cur = token->point;
+    translate_point(drawing, &cur);
+    int x2 = cur.x;
+    int y2 = cur.y;
+    token = token->next;
+    cur = token->point;
+    translate_point(drawing, &cur);
+    int x3 = cur.x;
+    int y3 = cur.y;
+
+    if (spline) {
+        // 1   [-1 +3 -3 +1]
+        // - * [+3 -6 +3  0]
+        // 6   [-3  0 +3  0]
+        //	   [+1 +4 +1  0]
+
+        double div6 = 1.0/6.0;
+
+        cx3 = div6*(-  x0+3*x1-3*x2+x3);
+        cx2 = div6*( 3*x0-6*x1+3*x2);
+        cx1 = div6*(-3*x0	   +3*x2);
+        cx0 = div6*(   x0+4*x1+1*x2);
+
+        cy3 = div6*(-  y0+3*y1-3*y2+y3);
+        cy2 = div6*( 3*y0-6*y1+3*y2);
+        cy1 = div6*(-3*y0     +3*y2);
+        cy0 = div6*(   y0+4*y1+1*y2);
+    } else {
+        // [-1 +3 -3 +1]
+        // [+3 -6 +3  0]
+        // [-3 +3  0  0]
+        // [+1  0  0  0]
+
+        cx3 = -  x0+3*x1-3*x2+x3;
+        cx2 =  3*x0-6*x1+3*x2;
+        cx1 = -3*x0+3*x1;
+        cx0 =    x0;
+
+        cy3 = -  y0+3*y1-3*y2+y3;
+        cy2 =  3*y0-6*y1+3*y2;
+        cy1 = -3*y0+3*y1;
+        cy0 =    y0;
+    }
+
+    max_accel1 = fabs(2 * cy2) + fabs(6 * cy3);
+    max_accel2 = fabs(2 * cx2) + fabs(6 * cx3);
+
+    max_accel = FFMAX(max_accel1, max_accel2);
+    h = 1.0;
+
+    if (max_accel > CURVE_ACCURACY)
+        h = sqrt(CURVE_ACCURACY / max_accel);
+
+    if (!started) {
+        cur.x = cx0;
+        cur.y = cy0;
+        drawing_add_point(drawing, &cur);
+    }
+
+    for (t = 0; t < 1.0; t += h) {
+        cur.x = cx0 + t * (cx1 + t * (cx2 + t * cx3));
+        cur.y = cy0 + t * (cy1 + t * (cy2 + t * cy3));
+        drawing_add_point(drawing, &cur);
+    }
+
+    cur.x = cx0 + cx1 + cx2 + cx3;
+    cur.y = cy0 + cy1 + cy2 + cy3;
+    drawing_add_point(drawing, &cur);
+}
+
+/*
+ * \brief Create and initialize a new drawing and return it
+ */
+ass_drawing_t *ass_drawing_new(void *fontconfig_priv, ass_font_t *font,
+                               ass_hinting_t hint, FT_Library lib)
+{
+    ass_drawing_t* drawing;
+
+    drawing = calloc(1, sizeof(*drawing));
+    drawing->text = malloc(DRAWING_INITIAL_SIZE);
+    drawing->size = DRAWING_INITIAL_SIZE;
+
+    drawing->ftlibrary = lib;
+    drawing_make_glyph(drawing, fontconfig_priv, font, hint);
+
+    drawing->scale_x = 1.;
+    drawing->scale_y = 1.;
+    drawing->max_contours = GLYPH_INITIAL_CONTOURS;
+    drawing->max_points = GLYPH_INITIAL_POINTS;
+
+    return drawing;
+}
+
+/*
+ * \brief Free a drawing
+ */
+void ass_drawing_free(ass_drawing_t* drawing)
+{
+    free(drawing->text);
+    free(drawing);
+}
+
+/*
+ * \brief Add one ASCII character to the drawing text buffer
+ */
+void ass_drawing_add_char(ass_drawing_t* drawing, char symbol)
+{
+    drawing->text[drawing->i++] = symbol;
+    drawing->text[drawing->i] = 0;
+
+    if (drawing->i + 1 >= drawing->size) {
+        drawing->size *= 2;
+        drawing->text = realloc(drawing->text, drawing->size);
+    }
+}
+
+/*
+ * \brief Create a hashcode for the drawing
+ * XXX: To avoid collisions a better hash algorithm might be useful.
+ */
+void ass_drawing_hash(ass_drawing_t* drawing)
+{
+    drawing->hash = fnv_32a_str(drawing->text, FNV1_32A_INIT);
+}
+
+/*
+ * \brief Convert token list to outline.  Calls the line and curve evaluators.
+ */
+FT_OutlineGlyph *ass_drawing_parse(ass_drawing_t *drawing)
+{
+    int started = 0;
+    ass_drawing_token_t *token;
+    FT_Vector pen = {0, 0};
+
+    drawing->tokens = drawing_tokenize(drawing->text);
+    drawing_prepare(drawing);
+
+    token = drawing->tokens;
+    while (token) {
+        // Draw something according to current command
+        switch (token->type) {
+        case TOKEN_MOVE_NC:
+            pen = token->point;
+            translate_point(drawing, &pen);
+            token = token->next;
+            break;
+        case TOKEN_MOVE:
+            pen = token->point;
+            translate_point(drawing, &pen);
+            if (started) {
+                drawing_close_shape(drawing);
+                started = 0;
+            }
+            token = token->next;
+            break;
+        case TOKEN_LINE: {
+            FT_Vector to;
+            to = token->point;
+            translate_point(drawing, &to);
+            if (!started) drawing_add_point(drawing, &pen);
+            drawing_add_point(drawing, &to);
+            started = 1;
+            token = token->next;
+            break;
+        }
+        case TOKEN_CUBIC_BEZIER:
+            if (token_check_values(token, 3, TOKEN_CUBIC_BEZIER) &&
+                token->prev) {
+                drawing_evaluate_curve(drawing, token->prev, 0, started);
+                token = token->next;
+                token = token->next;
+                token = token->next;
+                started = 1;
+            } else
+                token = token->next;
+            break;
+        case TOKEN_B_SPLINE:
+            if (token_check_values(token, 3, TOKEN_B_SPLINE) &&
+                token->prev) {
+                drawing_evaluate_curve(drawing, token->prev, 1, started);
+                token = token->next;
+                started = 1;
+            } else
+                token = token->next;
+            break;
+        default:
+            token = token->next;
+            break;
+        }
+    }
+
+    drawing_finish(drawing);
+    drawing_free_tokens(drawing->tokens);
+    return &drawing->glyph;
+}
+
+
diff --git a/libass/ass_drawing.h b/libass/ass_drawing.h
new file mode 100644
index 0000000..323c05d
--- /dev/null
+++ b/libass/ass_drawing.h
@@ -0,0 +1,76 @@
+/*
+ * Copyright (C) 2009 Grigori Goronzy <greg@geekmind.org>
+ *
+ * This file is part of libass.
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#ifndef LIBASS_DRAWING_H
+#define LIBASS_DRAWING_H
+
+#include <ft2build.h>
+#include FT_GLYPH_H
+
+#include "ass.h"
+
+#define DRAWING_INITIAL_SIZE 256
+
+enum ass_token_type {
+    TOKEN_MOVE,
+    TOKEN_MOVE_NC,
+    TOKEN_LINE,
+    TOKEN_CUBIC_BEZIER,
+    TOKEN_CONIC_BEZIER,
+    TOKEN_B_SPLINE,
+    TOKEN_EXTEND_SPLINE,
+    TOKEN_CLOSE
+};
+
+typedef struct ass_drawing_token_s {
+    enum ass_token_type type;
+    FT_Vector point;
+    struct ass_drawing_token_s *next;
+    struct ass_drawing_token_s *prev;
+} ass_drawing_token_t;
+
+typedef struct ass_drawing_s {
+    char *text; // drawing string
+    int i;      // text index
+    int scale;  // scale (1-64) for subpixel accuracy
+    double pbo; // drawing will be shifted in y direction by this amount
+    double scale_x;     // FontScaleX
+    double scale_y;     // FontScaleY
+    int asc;            // ascender
+    int desc;           // descender
+    FT_OutlineGlyph glyph;  // the "fake" glyph created for later rendering
+    int hash;           // hash value (for caching)
+
+    // private
+    FT_Library ftlibrary;   // FT library instance, needed for font ops
+    int size;           // current buffer size
+    ass_drawing_token_t *tokens;    // tokenized drawing
+    int max_points;     // current maximum size
+    int max_contours;
+    double point_scale_x;
+    double point_scale_y;
+} ass_drawing_t;
+
+ass_drawing_t *ass_drawing_new(void *fontconfig_priv, ass_font_t *font,
+                               ass_hinting_t hint, FT_Library lib);
+void ass_drawing_free(ass_drawing_t* drawing);
+void ass_drawing_add_char(ass_drawing_t* drawing, char symbol);
+void ass_drawing_hash(ass_drawing_t* drawing);
+FT_OutlineGlyph *ass_drawing_parse(ass_drawing_t *drawing);
+
+#endif /* LIBASS_DRAWING_H */
diff --git a/libass/ass_render.c b/libass/ass_render.c
index cc8242f..c112399 100644
--- a/libass/ass_render.c
+++ b/libass/ass_render.c
@@ -36,6 +36,7 @@
 #include "ass_utils.h"
 #include "ass_fontconfig.h"
 #include "ass_library.h"
+#include "ass_drawing.h"
 
 #define MAX_GLYPHS_INITIAL 1024
 #define MAX_LINES_INITIAL 64
@@ -171,6 +172,7 @@ typedef struct render_context_s {
     double shadow_x;
     double shadow_y;
     int drawing_mode;           // not implemented; when != 0 text is discarded, except for style override tags
+    ass_drawing_t *drawing;     // current drawing
 
     effect_t effect_type;
     int effect_timing;
@@ -1560,12 +1562,15 @@ static char *parse_tag(ass_renderer_t *render_priv, char *p, double pwr)
             val = 0.;
         render_priv->state.shadow_x = render_priv->state.shadow_y = val;
     } else if (mystrcmp(&p, "pbo")) {
-        int val = 0;
-        mystrtoi(&p, &val);     // ignored
+        double val = 0;
+        if (mystrtod(&p, &val))
+            render_priv->state.drawing->pbo = val;
     } else if (mystrcmp(&p, "p")) {
         int val;
         if (!mystrtoi(&p, &val))
             val = 0;
+        if (val)
+            render_priv->state.drawing->scale = val;
         render_priv->state.drawing_mode = !!val;
     }
 
@@ -1765,12 +1770,18 @@ init_render_context(ass_renderer_t *render_priv, ass_event_t *event)
     render_priv->state.effect_type = EF_NONE;
     render_priv->state.effect_timing = 0;
     render_priv->state.effect_skip_timing = 0;
+    render_priv->state.drawing =
+        ass_drawing_new(render_priv->fontconfig_priv,
+                        render_priv->state.font,
+                        render_priv->settings.hinting,
+                        render_priv->ftlibrary);
 
     apply_transition_effects(render_priv, event);
 }
 
-static void free_render_context(void)
+static void free_render_context(ass_renderer_t *render_priv)
 {
+    ass_drawing_free(render_priv->state.drawing);
 }
 
 // Calculate the cbox of a series of points
@@ -1867,23 +1878,33 @@ static void fix_freetype_stroker(FT_OutlineGlyph glyph, int border_x,
  */
 static void
 get_outline_glyph(ass_renderer_t *render_priv, int symbol,
-                  glyph_info_t *info, FT_Vector *advance)
+                  glyph_info_t *info, FT_Vector *advance,
+                  ass_drawing_t *drawing)
 {
     int error;
     glyph_hash_val_t *val;
     glyph_hash_key_t key;
     memset(&key, 0, sizeof(key));
-    key.font = render_priv->state.font;
-    key.size = render_priv->state.font_size;
-    key.ch = symbol;
-    key.scale_x = double_to_d16(render_priv->state.scale_x);
-    key.scale_y = double_to_d16(render_priv->state.scale_y);
-    key.advance = *advance;
-    key.bold = render_priv->state.bold;
-    key.italic = render_priv->state.italic;
-    key.outline.x = render_priv->state.border_x * 0xFFFF;
-    key.outline.y = render_priv->state.border_y * 0xFFFF;
 
+    if (drawing->hash) {
+        key.scale_x = double_to_d16(render_priv->state.scale_x);
+        key.scale_y = double_to_d16(render_priv->state.scale_y);
+        key.advance = *advance;
+        key.outline.x = render_priv->state.border_x * 0xFFFF;
+        key.outline.y = render_priv->state.border_y * 0xFFFF;
+        key.drawing_hash = drawing->hash;
+    } else {
+        key.font = render_priv->state.font;
+        key.size = render_priv->state.font_size;
+        key.ch = symbol;
+        key.bold = render_priv->state.bold;
+        key.italic = render_priv->state.italic;
+        key.scale_x = double_to_d16(render_priv->state.scale_x);
+        key.scale_y = double_to_d16(render_priv->state.scale_y);
+        key.advance = *advance;
+        key.outline.x = render_priv->state.border_x * 0xFFFF;
+        key.outline.y = render_priv->state.border_y * 0xFFFF;
+    }
     memset(info, 0, sizeof(glyph_info_t));
 
     val = cache_find_glyph(render_priv->cache.glyph_cache, &key);
@@ -1894,12 +1915,21 @@ get_outline_glyph(ass_renderer_t *render_priv, int symbol,
         info->bbox = val->bbox_scaled;
         info->advance.x = val->advance.x;
         info->advance.y = val->advance.y;
+        if (drawing->hash) {
+            drawing->asc = val->asc;
+            drawing->desc = val->desc;
+        }
     } else {
         glyph_hash_val_t v;
-        info->glyph =
-            ass_font_get_glyph(render_priv->fontconfig_priv,
-                               render_priv->state.font, symbol,
-                               render_priv->settings.hinting);
+        if (drawing->hash) {
+            ass_drawing_parse(drawing);
+            FT_Glyph_Copy((FT_Glyph) drawing->glyph, &info->glyph);
+        } else {
+            info->glyph =
+                ass_font_get_glyph(render_priv->fontconfig_priv,
+                                   render_priv->state.font, symbol,
+                                   render_priv->settings.hinting);
+        }
         if (!info->glyph)
             return;
         info->advance.x = d16_to_d6(info->glyph->advance.x);
@@ -1953,6 +1983,10 @@ get_outline_glyph(ass_renderer_t *render_priv, int symbol,
             FT_Glyph_Copy(info->outline_glyph, &v.outline_glyph);
         v.advance = info->advance;
         v.bbox_scaled = info->bbox;
+        if (drawing->hash) {
+            v.asc = drawing->asc;
+            v.desc = drawing->desc;
+        }
         cache_add_glyph(render_priv->cache.glyph_cache, &key, &v);
     }
 }
@@ -2433,6 +2467,7 @@ ass_render_event(ass_renderer_t *render_priv, ass_event_t *event,
     double device_x = 0;
     double device_y = 0;
     text_info_t *text_info = &render_priv->text_info;
+    ass_drawing_t *drawing;
 
     if (event->Style >= render_priv->track->n_styles) {
         ass_msg(MSGL_WARN, MSGTR_LIBASS_NoStyleFound);
@@ -2445,6 +2480,7 @@ ass_render_event(ass_renderer_t *render_priv, ass_event_t *event,
 
     init_render_context(render_priv, event);
 
+    drawing = render_priv->state.drawing;
     text_info->length = 0;
     pen.x = 0;
     pen.y = 0;
@@ -2457,11 +2493,25 @@ ass_render_event(ass_renderer_t *render_priv, ass_event_t *event,
         // this affects render_context
         do {
             code = get_next_char(render_priv, &p);
+            if (render_priv->state.drawing_mode && code)
+                ass_drawing_add_char(drawing, (char) code);
         } while (code && render_priv->state.drawing_mode);      // skip everything in drawing mode
 
+        // Parse drawing
+        if (drawing->i) {
+            drawing->scale_x = render_priv->state.scale_x *
+                                     render_priv->font_scale_x *
+                                     render_priv->font_scale;
+            drawing->scale_y = render_priv->state.scale_y *
+                                     render_priv->font_scale;
+            ass_drawing_hash(drawing);
+            p--;
+            code = -1;
+        }
+
         // face could have been changed in get_next_char
         if (!render_priv->state.font) {
-            free_render_context();
+            free_render_context(render_priv);
             return 1;
         }
 
@@ -2485,7 +2535,7 @@ ass_render_event(ass_renderer_t *render_priv, ass_event_t *event,
         }
 
         // Add kerning to pen
-        if (previous && code) {
+        if (previous && code && !drawing->hash) {
             FT_Vector delta;
             delta =
                 ass_font_get_kerning(render_priv->state.font, previous,
@@ -2500,7 +2550,8 @@ ass_render_event(ass_renderer_t *render_priv, ass_event_t *event,
                                render_priv->state.scale_y, &shift);
 
         get_outline_glyph(render_priv, code,
-                          text_info->glyphs + text_info->length, &shift);
+                          text_info->glyphs + text_info->length, &shift,
+                          drawing);
 
         text_info->glyphs[text_info->length].pos.x = pen.x;
         text_info->glyphs[text_info->length].pos.y = pen.y;
@@ -2539,19 +2590,34 @@ ass_render_event(ass_renderer_t *render_priv, ass_event_t *event,
         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);
-        text_info->glyphs[text_info->length].asc *=
-            render_priv->state.scale_y;
-        text_info->glyphs[text_info->length].desc *=
-            render_priv->state.scale_y;
+        if (drawing->hash) {
+            text_info->glyphs[text_info->length].asc = drawing->asc;
+            text_info->glyphs[text_info->length].desc = drawing->desc;
+        } else {
+            ass_font_get_asc_desc(render_priv->state.font, code,
+                                  &text_info->glyphs[text_info->length].asc,
+                                  &text_info->glyphs[text_info->length].desc);
+
+            text_info->glyphs[text_info->length].asc *=
+                render_priv->state.scale_y;
+            text_info->glyphs[text_info->length].desc *=
+                render_priv->state.scale_y;
+        }
 
         // fill bitmap_hash_key
-        text_info->glyphs[text_info->length].hash_key.font =
-            render_priv->state.font;
-        text_info->glyphs[text_info->length].hash_key.size =
-            render_priv->state.font_size;
+        if (!drawing->hash) {
+            text_info->glyphs[text_info->length].hash_key.font =
+                render_priv->state.font;
+            text_info->glyphs[text_info->length].hash_key.size =
+                render_priv->state.font_size;
+            text_info->glyphs[text_info->length].hash_key.bold =
+                render_priv->state.bold;
+            text_info->glyphs[text_info->length].hash_key.italic =
+                render_priv->state.italic;
+        } else
+            text_info->glyphs[text_info->length].hash_key.drawing_hash =
+                drawing->hash;
+        text_info->glyphs[text_info->length].hash_key.ch = code;
         text_info->glyphs[text_info->length].hash_key.outline.x =
             render_priv->state.border_x * 0xFFFF;
         text_info->glyphs[text_info->length].hash_key.outline.y =
@@ -2570,11 +2636,6 @@ ass_render_event(ass_renderer_t *render_priv, ass_event_t *event,
             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 =
-            render_priv->state.italic;
-        text_info->glyphs[text_info->length].hash_key.ch = code;
         text_info->glyphs[text_info->length].hash_key.advance.x = pen.x;
         text_info->glyphs[text_info->length].hash_key.advance.y = pen.y;
         text_info->glyphs[text_info->length].hash_key.be =
@@ -2597,11 +2658,20 @@ ass_render_event(ass_renderer_t *render_priv, ass_event_t *event,
         render_priv->state.effect_type = EF_NONE;
         render_priv->state.effect_timing = 0;
         render_priv->state.effect_skip_timing = 0;
+
+        if (drawing->hash) {
+            ass_drawing_free(drawing);
+            drawing = render_priv->state.drawing =
+                ass_drawing_new(render_priv->fontconfig_priv,
+                    render_priv->state.font,
+                    render_priv->settings.hinting,
+                    render_priv->ftlibrary);
+        }
     }
 
     if (text_info->length == 0)