* docs/DEBUG.TXT: adding debugging support documentation

    * src/base/ftdebug.c (ft_debug_init), builds/win32/ftdebug.c
    (ft_debug_init), builds/amiga/src/ftdebug.c (ft_debug_init): changed the
    syntax of the FT2_DEBUG environment variable  used to control debugging
    output (i.e. logging and error messages). It must now look like:

       any:6 memory:4 io:3   or
       any:6,memory:4,io:3   or
       any:6;memory:4;io:3

1 files changed, 164 insertions, 0 deletions

diff --git a/docs/DEBUG.TXT b/docs/DEBUG.TXT
new file mode 100644
index 000000000..86ffbcfa5
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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 controled 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
+    used to print error messages during program execution. This will not
+    stop the program, but is very useful to spot invalid fonts during
+    development and code wordarounds for them.
+
+
+  FT_DEBUG_LEVEL_TRACE ::
+
+    #define this macro if you want to compile both the FT_ERROR macro and
+    the FT_TRACE one. This also includes the variants FT_TRACE0, FT_TRACE1,
+    FT_TRACE2, ..., FT_TRACE6.
+
+    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 ::
+
+    when this macro is #defined, the FreeType engines 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's 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 un-affected.
+
+
+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 must use with 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 6
+   when a program linked with FreeType starts, through the use of the FT2_DEBUG
+   environment variable, described later.
+
+   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 print-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_TRACE6 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, and "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)
+
+    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 leaked memory blocks as well as other common
+    errors like double frees. It is also capable of reporting _where_ the
+    leaked 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.
+
+
+Voila,
+
+- David Turner
+
+
+
+    used like printf( format, ... ), but with double quotes. This will
+    send a message to the standard error descriptor (stderr on most systems)
+    in certain builds of the library
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