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kc3-lang/freetype/docs/DEBUG
Werner Lemberg
- docs/DEBUG
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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 `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 2002-2015 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 ---