217 lines
8.1 KiB
Plaintext
217 lines
8.1 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
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builds. This is controlled through the definition of special macros
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located in the file `ftoption.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
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calls to print error messages during program execution. This does
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not stop the program. Very useful to spot invalid fonts during
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development and to code workarounds for them.
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FT_DEBUG_LEVEL_TRACE
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#define this macro if you want to compile both macros `FT_ERROR'
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and `FT_TRACE'. This also includes the variants `FT_TRACE0',
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`FT_TRACE1', `FT_TRACE2', ..., `FT_TRACE7'.
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The trace macros are used to send debugging messages when an
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appropriate `debug level' is configured at runtime through the
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`FT2_DEBUG' environment variable (more on this later).
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FT_DEBUG_MEMORY
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If this macro is #defined, the FreeType engine is linked with a
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small but effective debugging memory manager that tracks all
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allocations and frees that are performed within the font engine.
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When the `FT2_DEBUG_MEMORY' environment variable is defined at
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runtime, a call to `FT_Done_FreeType' dumps memory statistics,
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including the list of leaked memory blocks and optionally with the
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source locations where these were allocated. It is always a very
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good idea to define this in development builds. This works with
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_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
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memory manager is ignored, and performance is unaffected.
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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
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debugging its code:
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1. FT_ERROR(( ... ))
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This macro is used to send debug messages that indicate relatively
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serious errors (like broken font files) without stopping the
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execution of the running program. Its code is compiled only when
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either `FT_DEBUG_LEVEL_ERROR' or `FT_DEBUG_LEVEL_TRACE' are
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defined in `ftoption.h'.
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Note that you have to use 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
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condition isn't TRUE, the program aborts with a panic message.
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Its code is compiled when either `FT_DEBUG_LEVEL_ERROR' or
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`FT_DEBUG_LEVEL_TRACE' are defined. You don't need double
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parentheses here. 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
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messages during program execution. This macro uses an *implicit*
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macro named `FT_COMPONENT', which names the current FreeType
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component being run.
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The developer should always define `FT_COMPONENT' as appropriate,
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for example as in
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#undef FT_COMPONENT
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#define FT_COMPONENT io
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The value of the `FT_COMPONENT' macro is one of the component
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names defined in the internal file `internal/fttrace.h'. If you
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modify the FreeType source code and insert a new `FT_COMPONENT'
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macro, you must register it in `fttrace.h'. If you insert or
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remove many trace macros, you can test for undefined or unused
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trace macros with the script `src/tools/chktrcmp.py'.
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Each such component is assigned a `debug level', ranging from
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value 0 to 7, through the use of the `FT2_DEBUG' environment
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variable (described below) when a program linked with FreeType
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starts.
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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
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the corresponding component level are filtered out and never
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printed. This means that trace messages with level 0 are always
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printed, those with level 2 are only printed when the component
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level is *at least* 2, etc.
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The second parameter to `FT_TRACE' must contain parentheses and
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corresponds to a printf-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', ...,
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`FT_TRACE7' can be used with constant level indices, and are much
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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
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behaviour of FreeType at runtime.
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FT2_DEBUG
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This variable is only used when FreeType is built with
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`FT_DEBUG_LEVEL_TRACE' defined. It contains a list of component
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level definitions, following this 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
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in `fttrace.h'. `levelX' is the corresponding level to use at
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runtime.
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`any' is a special component name that is interpreted as `any/all
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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 with bash)
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both stipulate that all components should have level 2, except for
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the memory and io components, which are set to the trace levels 5
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and 4, respectively.
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FT2_DEBUG_MEMORY
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This environment variable, when defined, tells FreeType to use a
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debugging memory manager that tracks leaking memory blocks as well
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as other common errors like double frees. It is also capable of
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reporting _where_ the leaking blocks were allocated, which
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considerably saves time when debugging new additions to the
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library.
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This code is only compiled when FreeType is built with the
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`FT_DEBUG_MEMORY' macro #defined in `ftoption.h' though, it is
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ignored in other builds.
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FT2_ALLOC_TOTAL_MAX
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This variable is ignored if `FT2_DEBUG_MEMORY' is not defined. It
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allows you to specify a maximum heap size for all memory
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allocations performed by FreeType. This is very useful to test
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the robustness of the font engine and programs that use it in
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tight memory conditions.
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If it is undefined, or if its value is not strictly positive, no
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allocation bounds are checked at runtime.
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FT2_ALLOC_COUNT_MAX
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This variable is ignored if `FT2_DEBUG_MEMORY' is not defined. It
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allows you to specify a maximum number of memory allocations
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performed by FreeType before returning the error
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`FT_Err_Out_Of_Memory'. This is useful for debugging and testing
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the engine's robustness.
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If it is undefined, or if its value is not strictly positive, no
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allocation bounds are checked at runtime.
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FT2_KEEP_ALIVE
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This variable is ignored if `FT2_DEBUG_MEMORY' is not defined.
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`Keep alive' means that freed blocks aren't released to the heap.
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This is useful to detect double-frees or weird heap corruption,
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reporting the source code location of the original allocation and
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deallocation in case of a problem. It uses large amounts of
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memory, however.
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If it is undefined, or if its value is not strictly positive,
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freed blocks are released at runtime.
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------------------------------------------------------------------------
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Copyright (C) 2002-2020 by
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David Turner, Robert Wilhelm, and Werner Lemberg.
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This file is part of the FreeType project, and may only be used,
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modified, and distributed under the terms of the FreeType project
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license, LICENSE.TXT. By continuing to use, modify, or distribute this
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file you indicate that you have read the license and understand and
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accept it fully.
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--- end of DEBUG ---
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