Debugging within the FreeType sources=====================================I. Configuration macros-----------------------There  are several ways  to enable  debugging features  in a  FreeType 2builds.   This is controlled  through the  definition of  special macroslocated in the file "ftoptions.h".  The macros are:  FT_DEBUG_LEVEL_ERROR    #define this macro  if you want to compile  the FT_ERROR macro calls    to  print error messages  during program  execution.  This  will not    stop  the  program.   Very  useful  to  spot  invalid  fonts  during    development and to code workarounds for them.  FT_DEBUG_LEVEL_TRACE    #define this macro  if you want to compile  both macros FT_ERROR and    FT_TRACE.   This also  includes the  variants  FT_TRACE0, FT_TRACE1,    FT_TRACE2, ..., FT_TRACE7.    The  trace  macros are  used  to  send  debugging messages  when  an    appropriate  "debug  level" is  configured  at  runtime through  the    FT2_DEBUG environment variable (more on this later).  FT_DEBUG_MEMORY    If  this macro is  #defined, the  FreeType engine  is linked  with a    small  but  effective  debugging  memory  manager  that  tracks  all    allocations and frees that are performed within the font engine.    When  the  FT2_DEBUG_MEMORY   environment  variable  is  defined  at    runtime,  a call  to FT_Done_FreeType  will dump  memory statistics,    including the list of leaked memory blocks with the source locations    where these were allocated.  It is always a very good idea to define    this in development builds.  This works with _any_ program linked to    FreeType, but  requires a big  deal of memory (the  debugging memory    manager never frees the blocks to the heap in order to detect double    frees).    When FT2_DEBUG_MEMORY isn't defined at runtime, the debugging memory    manager is ignored, and performance is unaffected.II. Debugging macros--------------------Several macros can be used within the FreeType sources to help debuggingits code:  1. FT_ERROR(( ... ))    This macro is  used to send debug messages  that indicate relatively    serious  errors (like  broken font  files),  but will  not stop  the    execution of  the running program.   Its code is compiled  only when    either FT_DEBUG_LEVEL_ERROR  or FT_DEBUG_LEVEL_TRACE are  defined in    "ftoption.h".    Note that you  have to use a printf-like  signature, but with double    parentheses, like in:      FT_ERROR(( "your %s is not %s\n", "foo", "bar" ));  2. FT_ASSERT( condition )    This macro  is used to check  strong assertions at  runtime.  If its    condition isn't TRUE,  the program will abort with  a panic message.    Its   code   is  compiled   when   either  FT_DEBUG_LEVEL_ERROR   or    FT_DEBUG_LEVEL_TRACE are defined.  You don't need double-parentheses    here.  For example:      FT_ASSERT( ptr != NULL );  3. FT_TRACE( level, (message...) )    The  FT_TRACE  macro  is  used  to  send  general-purpose  debugging    messages during  program execution.   This macro uses  an *implicit*    macro named FT_COMPONENT used to name the current FreeType component    being run.    The developer should always  define FT_COMPONENT as appropriate, for    example as in:      #undef  FT_COMPONENT      #define FT_COMPONENT  trace_io    The  value  of  the  FT_COMPONENT  macro  is  an  enumeration  named    trace_XXXX where XXXX  is one of the component  names defined in the    internal file <freetype/internal/fttrace.h>.    Each  such component  is assigned  a "debug  level", ranging  from 0    to 7,  through  the  use   of  the  FT2_DEBUG  environment  variable    (described below) when a program linked with FreeType starts.    When FT_TRACE  is called, its  level is compared  to the one  of the    corresponding component.   Messages with trace  levels *higher* than    the corresponding component level are filtered and never printed.    This  means that  trace messages  with level  0 are  always printed,    those with level 2 are only  printed when the component level is *at    least* 2.    The  second  parameter  to  FT_TRACE must  contain  parentheses  and    correspond to a printf-like call, as in:      FT_TRACE( 2, ( "your %s is not %s\n", "foo", "bar" ) )    The shortcut macros  FT_TRACE0, FT_TRACE1, FT_TRACE2_, ... FT_TRACE7    can be  used with  constant level indices,  and are much  cleaner to    use, as in     FT_TRACE2(( "your %s is not %s\n", "foo", "bar" ));III. Environment variables--------------------------The  following  environment   variables  control  debugging  output  andbehaviour of FreeType at runtime:  FT2_DEBUG    This   variable  is   only  used   when  FreeType   is   built  with    FT_DEBUG_LEVEL_TRACE defined.  It contains a list of component level    definitions, following this format:       component1:level1 component2:level2 component3:level3 ...    where "componentX" is the name of a tracing component, as defined in    "fttrace.h",  but  without the  "trace_"  prefix.   "levelX" is  the    corresponding level to use at runtime.    "any"  is a  special  component  name that  will  be interpreted  as    "any/all components".  For example, the following definitions       set FT2_DEBUG=any:2 memory:5 io:4        (on Windows)       export FT2_DEBUG="any:2 memory:5 io:4"   (on Linux with bash)    both stipulate that  all components should have level  2, except for    the memory  and io components  which will be  set to trace  levels 5    and 4, respectively.  FT2_DEBUG_MEMORY    This  environment variable, when  defined, tells  FreeType to  use a    debugging memory  manager that will  track leaking memory  blocks as    well as other  common errors like double frees.   It is also capable    of  reporting  _where_  the  leaking blocks  were  allocated,  which    considerably saves time when debugging new additions to the library.    This  code  is  only  compiled  when  FreeType  is  built  with  the    FT_DEBUG_MEMORY macro  #defined in  "ftoption.h" though, it  will be    ignored in other builds.  FT2_ALLOC_TOTAL_MAX    This  variable is ignored  if FT2_DEBUG_MEMORY  is not  defined.  It    allows you to specify a maximum heap size for all memory allocations    performed by FreeType.   This is very useful to  test the robustness    of  the  font  engine and  programs  that  use  it in  tight  memory    conditions.        If it is  undefined, or if its value is  not strictly positive, then    no allocation bounds are checked at runtime.  FT2_ALLOC_COUNT_MAX      This  variable is ignored  if FT2_DEBUG_MEMORY  is not  defined.  It    allows  you  to  specify  a  maximum number  of  memory  allocations    performed    by     FreeType    before    returning     the    error    FT_Err_Out_Of_Memory.  This is useful  for debugging and testing the    engine's robustness.        If it is  undefined, or if its value is  not strictly positive, then    no allocation bounsd are checked at runtime.------------------------------------------------------------------------Copyright 2002, 2003, 2004 byDavid Turner, Robert Wilhelm, and Werner Lemberg.This  file  is  part  of the  FreeType  project, and may  only be  used,modified,  and  distributed  under  the  terms of  the FreeType  projectlicense, LICENSE.TXT.   By continuing to use, modify, or distribute thisfile you  indicate that  you have  read the  license and understand  andaccept it fully.--- end of DEBUG ---