02c3aede1b
* 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
164 lines
5.9 KiB
Plaintext
164 lines
5.9 KiB
Plaintext
Debugging within the FreeType sources:
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======================================
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I. Configuration macros:
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========================
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There are several ways to enable debugging features in a FreeType 2 builds.
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This is controled through the definition of special macros located in the
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file "ftoptions.h". The macros are:
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FT_DEBUG_LEVEL_ERROR ::
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#define this macro if you want to compile the FT_ERROR macro calls
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used to print error messages during program execution. This will not
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stop the program, but is very useful to spot invalid fonts during
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development and code wordarounds for them.
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FT_DEBUG_LEVEL_TRACE ::
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#define this macro if you want to compile both the FT_ERROR macro and
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the FT_TRACE one. This also includes the variants FT_TRACE0, FT_TRACE1,
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FT_TRACE2, ..., FT_TRACE6.
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The trace macros are used to send debugging messages when an appropriate
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"debug level" is configured at runtime through the FT2_DEBUG environment
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variable (more on this later)
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FT_DEBUG_MEMORY ::
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when this macro is #defined, the FreeType engines is linked with a small
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but effective debugging memory manager that tracks all allocations and
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frees that are performed within the font engine.
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When the FT2_DEBUG_MEMORY environment variable is defined at runtime, a
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call to FT_Done_FreeType will dump memory statistics, including the list of
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leaked memory blocks with the source locations where these were allocated.
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It's always a very good idea to define this in development builds. This
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works with _any_ program linked to FreeType, but requires a big deal of
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memory (the debugging memory manager never frees the blocks to the
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heap in order to detect double frees).
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When FT2_DEBUG_MEMORY isn't defined at runtime, the debugging memory
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manager is ignored, and performance is un-affected.
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II. Debugging macros:
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=====================
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Several macros can be used within the FreeType sources to help debugging
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its code:
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1. FT_ERROR(( .. ))
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this macro is used to send debug messages that indicate relatively serious
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errors (like broken font files), but will not stop the execution of the
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running program. Its code is compiled only when either FT_DEBUG_LEVEL_ERROR
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or FT_DEBUG_LEVEL_TRACE are defined in "ftoption.h"
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Note that you must use with a printf-like signature, but with double
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parentheses, like in:
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FT_ERROR(( "your %s is not %s\n", "foo", "bar" ));
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2. FT_ASSERT( condition )
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this macro is used to check strong assertions at runtime. If its condition
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isn't TRUE, the program will abort with a panic message. Its code is
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compiled when either FT_DEBUG_LEVEL_ERROR or FT_DEBUG_LEVEL_TRACE are
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defined. You don't need double-parentheses here. For example:
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FT_ASSERT( ptr != NULL );
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3. FT_TRACE( level, (message...) )
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the FT_TRACE macro is used to send general-purpose debugging messages
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during program execution. This macro uses an *implicit* macro named
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FT_COMPONENT used to name the current FreeType component being run.
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The developer should always define FT_COMPONENT as appropriate, for
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example as in:
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#undef FT_COMPONENT
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#define FT_COMPONENT trace_io
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the value of the FT_COMPONENT macro is an enumeration named trace_XXXX
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where XXXX is one of the component names defined in the internal file
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<freetype/internal/fttrace.h>
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Each such component is assigned a "debug level", ranging from 0 to 6
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when a program linked with FreeType starts, through the use of the FT2_DEBUG
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environment variable, described later.
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When FT_TRACE is called, its level is compared to the one of the
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corresponding component. Messages with trace levels *higher* than the
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corresponding component level are filtered and never printed.
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this means that trace messages with level 0 are always printed, those
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with level 2 are only printed when the component level is *at least* 2
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The second parameter to FT_TRACE must contain parentheses and correspond
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to a print-like call, as in:
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FT_TRACE( 2, ( "your %s is not %s\n", "foo", "bar" ) )
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The shortcut macros FT_TRACE0, FT_TRACE1, FT_TRACE2_, ... FT_TRACE6 can
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be used with constant level indices, and are much cleaner to use, as in
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FT_TRACE2(( "your %s is not %s\n", "foo", "bar" ));
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III. Environment variables:
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===========================
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The following environment variables control debugging output and behaviour
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of FreeType at runtime:
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FT2_DEBUG
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this variable is only used when FreeType is built with FT_DEBUG_LEVEL_TRACE
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defined. It contains a list of component level definitions, following this
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format:
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component1:level1 component2:level2 component3:level3 ...
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where "componentX" is the name of a tracing component, as defined in
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"fttrace.h", but without the "trace_" prefix, and "levelX" is the
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corresponding level to use at runtime.
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"any" is a special component name that will be interpreted as
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"any/all components". For example, the following definitions
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set FT2_DEBUG=any:2 memory:5 io:4 (on Windows)
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export FT2_DEBUG="any:2 memory:5 io:4" (on Linux)
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both stipulate that all components should have level 2, except for the
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memory and io components which will be set to trace levels 5 and 4
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respectively.
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FT2_DEBUG_MEMORY
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this environment variable, when defined, tells FreeType to use a debugging
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memory manager that will track leaked memory blocks as well as other common
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errors like double frees. It is also capable of reporting _where_ the
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leaked blocks were allocated, which considerably saves time when
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debugging new additions to the library.
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This code is only compiled when FreeType is built with the FT_DEBUG_MEMORY
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macro #defined in "ftoption.h" though, it will be ignored in other builds.
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Voila,
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- David Turner
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used like printf( format, ... ), but with double quotes. This will
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send a message to the standard error descriptor (stderr on most systems)
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in certain builds of the library |