[wasm-api] Make buffer_copy_contents reuse contents

src/hb-wasm-api-buffer.hh

@@ -106,8 +106,30 @@ HB_WASM_API (bool_t, buffer_copy_contents) (HB_WASM_EXEC_ENV
 
   if (buffer->have_output)
     buffer->sync ();
+  if (!buffer->have_positions)
+    buffer->clear_positions ();
 
   unsigned length = buffer->len;
+
+  if (length <= contents->length)
+  {
+    unsigned bytes = length * sizeof (hb_glyph_info_t);
+
+    glyph_info_t *info = (glyph_info_t *) (validate_app_addr (contents->info, bytes) ? addr_app_to_native (contents->info) : nullptr);
+    glyph_position_t *pos = (glyph_position_t *) (validate_app_addr (contents->pos, bytes) ? addr_app_to_native (contents->pos) : nullptr);
+
+    if (unlikely (!info || !pos))
+    {
+      contents->length = 0;
+      return false;
+    }
+
+    memcpy (info, buffer->info, bytes);
+    memcpy (pos, buffer->pos, bytes);
+
+    return true;
+  }
+
   contents->length = length;
   contents->info = wasm_runtime_module_dup_data (module_inst, (const char *) buffer->info, length * sizeof (buffer->info[0]));
   contents->pos = wasm_runtime_module_dup_data (module_inst, (const char *) buffer->pos, length * sizeof (buffer->pos[0]));
@@ -141,7 +163,9 @@ HB_WASM_API (bool_t, buffer_set_contents) (HB_WASM_EXEC_ENV
   glyph_info_t *info = (glyph_info_t *) (validate_app_addr (contents->info, bytes) ? addr_app_to_native (contents->info) : nullptr);
   glyph_position_t *pos = (glyph_position_t *) (validate_app_addr (contents->pos, bytes) ? addr_app_to_native (contents->pos) : nullptr);
 
-  buffer->clear_positions (); /* This is wasteful, but we need it to set have_positions=true. */
+  if (!buffer->have_positions)
+    buffer->clear_positions (); /* This is wasteful. */
+
   memcpy (buffer->info, info, bytes);
   memcpy (buffer->pos, pos, bytes);
   buffer->len = length;

src/hb-wasm-api.h

@@ -139,6 +139,7 @@ typedef struct
   ptr_t(glyph_info_t) info;
   ptr_t(glyph_position_t) pos;
 } buffer_contents_t;
+#define BUFFER_CONTENTS_INIT {0, 0, 0}
 
 HB_WASM_API (bool_t, buffer_contents_realloc) (HB_WASM_EXEC_ENV
 					       ptr_d(buffer_contents_t, contents),

src/wasm/graphite/shape.cc

@@ -76,7 +76,7 @@ shape (void *shape_plan,
     direction = DIRECTION_REVERSE (direction);
   }
 
-  buffer_contents_t contents;
+  buffer_contents_t contents = BUFFER_CONTENTS_INIT;
   if (!buffer_copy_contents (buffer, &contents))
     return false;
 

src/wasm/sample/c/shape-fallback.cc

@@ -26,7 +26,7 @@ shape (void *shape_plan,
 
   blob_free (&blob);
 
-  buffer_contents_t contents;
+  buffer_contents_t contents = BUFFER_CONTENTS_INIT;
   if (!buffer_copy_contents (buffer, &contents))
     return false;