| 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 `ftoption.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 does |
| 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' dumps memory statistics, |
| including the list of leaked memory blocks and optionally 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. |
| |
| FT_DEBUG_LOGGING |
| |
| #define this macro for enhanced logging support; it automatically |
| sets `FT_DEBUG_LEVEL_TRACE' and `FT_DEBUG_LEVEL_ERROR'. |
| |
| If defined, `FT_TRACE' and `FT_ERROR' can send tracing and |
| debugging messages to a file. The location of the log file has to |
| be set with the `FT_LOGGING_FILE' environment variable (more on |
| this later). |
| |
| The main enhancements are the possibility of logging the time and |
| the name of the `FT_COMPONENT' macro together with the affected |
| `FT_TRACE' or `FT_ERROR' calls. See below how to activate this in |
| the `FT2_DEBUG' environment variable. |
| |
| |
| 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) without stopping 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 aborts 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. 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', which names 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 io |
| |
| The value of the `FT_COMPONENT' macro is one of the component |
| names defined in the internal file `internal/fttrace.h'. If you |
| modify the FreeType source code and insert a new `FT_COMPONENT' |
| macro, you must register it in `fttrace.h'. If you insert or |
| remove many trace macros, you can test for undefined or unused |
| trace macros with the script `src/tools/chktrcmp.py'. |
| |
| Each such component is assigned a `debug level', ranging from |
| value 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 out 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, etc. |
| |
| The second parameter to `FT_TRACE' must contain parentheses and |
| corresponds 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'. `levelX' is the corresponding level to use at |
| runtime. |
| |
| `any' is a special component name that is 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 are set to the trace levels 5 |
| and 4, respectively. |
| |
| If `FT_DEBUG_LOGGING' is defined, two more options are available. |
| |
| * -v: Print also the name of FreeType's component from which the |
| current log is produced, together with the tracing level. |
| |
| * -t: Print also the time. |
| |
| Here are some examples how the output might look like. |
| |
| FT2_DEBUG="any:7 memory:5 -vt" |
| |
| => [20:32:02:44969 ttload:2] table directory loaded |
| |
| FT2_DEBUG="any:7 memory:5 -t" |
| |
| => [20:32:02:44969] table directory loaded |
| |
| FT2_DEBUG="any:7 memory:5 -v" |
| |
| => [ttload:2] table directory loaded |
| |
| |
| FT_LOGGING_FILE |
| |
| This variable is only used if FreeType is built with the |
| `FT_DEBUG_LOGGING' macro defined. It contains the path to the |
| file where the user wants to put his log file. If it is not set, |
| FreeType uses stderr. |
| |
| Examples: |
| |
| On UNIX-like systems with bash: |
| export FT_LOGGING_FILE="/tmp/freetype2.log" |
| |
| On Windows: |
| set FT_LOGGING_FILE=C:\Users\AppData\Local\Temp\freetype2.log |
| |
| |
| FT2_DEBUG_MEMORY |
| |
| This environment variable, when defined, tells FreeType to use a |
| debugging memory manager that tracks 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 is |
| 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, 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, no |
| allocation bounds are checked at runtime. |
| |
| |
| FT2_KEEP_ALIVE |
| |
| This variable is ignored if `FT2_DEBUG_MEMORY' is not defined. |
| `Keep alive' means that freed blocks aren't released to the heap. |
| This is useful to detect double-frees or weird heap corruption, |
| reporting the source code location of the original allocation and |
| deallocation in case of a problem. It uses large amounts of |
| memory, however. |
| |
| If it is undefined, or if its value is not strictly positive, |
| freed blocks are released at runtime. |
| |
| |
| IV. Additional Capabilities with `FT_DEBUG_LOGGING' |
| --------------------------------------------------- |
| |
| If `FT_DEBUG_LOGGING' is defined, four APIs are available to provide |
| additional debugging support. Use |
| |
| #include <freetype/ftlogging.h> |
| |
| to access them. |
| |
| FT_Trace_Set_Level( const char* level ) |
| |
| By default, FreeType uses the tracing levels set in the |
| `FT2_DEBUG' environment variable. Use this function to override |
| the value with `level'. Use value `NULL' to disable tracing. |
| |
| FT_Trace_Set_Default_Level(): |
| |
| Reset the tracing levels to the default value, i.e., the value of |
| the `FT2_DEBUG' environment variable or no tracing if not set. |
| |
| FT_Set_Log_Handler( ft_custom_log_handler handler ): |
| |
| Use `handler' as a custom handler for formatting tracing and error |
| messages. The `ft_custom_log_handler' typedef has the following |
| prototype. |
| |
| void |
| (*ft_custom_log_handler)( const char* ft_component, |
| const char* fmt, |
| va_list args ); |
| |
| `ft_component' is the current component like `ttload', `fmt' is the |
| first argument of `FT_TRACE' or `FT_ERROR', and `args' holds the |
| remaining arguments. |
| |
| FT_Set_Default_Log_Handler(): |
| |
| Reset the log handler to the default version. |
| |
| |
| ------------------------------------------------------------------------ |
| |
| Copyright (C) 2002-2021 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 --- |
