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diff --git a/docs/DEBUG b/docs/DEBUG new file mode 100644 index 0000000..1fccc21 --- /dev/null +++ b/docs/DEBUG @@ -0,0 +1,199 @@ +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'. + + 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 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 --- |