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+Debugging within the FreeType sources
+=====================================
+
+I. Configuration macros
+-----------------------
+
+There are several ways to enable debugging features in a FreeType 2
+builds. This is controlled through the definition of special macros
+located 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 debugging
+its 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'. If you modify FreeType
+ source and insert new trace_XXXX macro, you must register it in
+ fttrace.h. If you insert or remove many trace macros, you can check
+ the undefined or the unused trace macro by src/tools/chktrcmp.py.
+
+ 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 and
+behaviour 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 bounds are checked at runtime.
+
+------------------------------------------------------------------------
+
+Copyright 2002, 2003, 2004, 2005, 2009 by
+David 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 project
+license, LICENSE.TXT. By continuing to use, modify, or distribute this
+file you indicate that you have read the license and understand and
+accept it fully.
+
+
+--- end of DEBUG ---