1 Debugging within the FreeType sources 2 ===================================== 3 4 I. Configuration macros 5 ----------------------- 6 7 There are several ways to enable debugging features in a FreeType 2 8 builds. This is controlled through the definition of special macros 9 located in the file `ftoption.h'. The macros are: 10 11 12 FT_DEBUG_LEVEL_ERROR 13 14 #define this macro if you want to compile the FT_ERROR macro calls 15 to print error messages during program execution. This will not 16 stop the program. Very useful to spot invalid fonts during 17 development and to code workarounds for them. 18 19 FT_DEBUG_LEVEL_TRACE 20 21 #define this macro if you want to compile both macros FT_ERROR and 22 FT_TRACE. This also includes the variants FT_TRACE0, FT_TRACE1, 23 FT_TRACE2, ..., FT_TRACE7. 24 25 The trace macros are used to send debugging messages when an 26 appropriate `debug level' is configured at runtime through the 27 FT2_DEBUG environment variable (more on this later). 28 29 FT_DEBUG_MEMORY 30 31 If this macro is #defined, the FreeType engine is linked with a 32 small but effective debugging memory manager that tracks all 33 allocations and frees that are performed within the font engine. 34 35 When the FT2_DEBUG_MEMORY environment variable is defined at 36 runtime, a call to FT_Done_FreeType will dump memory statistics, 37 including the list of leaked memory blocks with the source 38 locations where these were allocated. It is always a very good 39 idea to define this in development builds. This works with _any_ 40 program linked to FreeType, but requires a big deal of memory (the 41 debugging memory manager never frees the blocks to the heap in 42 order to detect double frees). 43 44 When FT2_DEBUG_MEMORY isn't defined at runtime, the debugging 45 memory manager is ignored, and performance is unaffected. 46 47 48 II. Debugging macros 49 -------------------- 50 51 Several macros can be used within the FreeType sources to help 52 debugging its code: 53 54 55 1. FT_ERROR(( ... )) 56 57 This macro is used to send debug messages that indicate relatively 58 serious errors (like broken font files), but will not stop the 59 execution of the running program. Its code is compiled only when 60 either FT_DEBUG_LEVEL_ERROR or FT_DEBUG_LEVEL_TRACE are defined in 61 `ftoption.h'. 62 63 Note that you have to use a printf-like signature, but with double 64 parentheses, like in 65 66 FT_ERROR(( "your %s is not %s\n", "foo", "bar" )); 67 68 69 2. FT_ASSERT( condition ) 70 71 This macro is used to check strong assertions at runtime. If its 72 condition isn't TRUE, the program will abort with a panic message. 73 Its code is compiled when either FT_DEBUG_LEVEL_ERROR or 74 FT_DEBUG_LEVEL_TRACE are defined. You don't need double 75 parentheses here. For example 76 77 FT_ASSERT( ptr != NULL ); 78 79 80 3. FT_TRACE( level, (message...) ) 81 82 The FT_TRACE macro is used to send general-purpose debugging 83 messages during program execution. This macro uses an *implicit* 84 macro named FT_COMPONENT used to name the current FreeType 85 component being run. 86 87 The developer should always define FT_COMPONENT as appropriate, 88 for example as in 89 90 #undef FT_COMPONENT 91 #define FT_COMPONENT trace_io 92 93 The value of the FT_COMPONENT macro is an enumeration named 94 `trace_XXXX' where `XXXX' is one of the component names defined in 95 the internal file `internal/fttrace.h'. If you modify FreeType 96 source and insert new `trace_XXXX' macro, you must register it in 97 `fttrace.h'. If you insert or remove many trace macros, you can 98 check the undefined or the unused trace macro by 99 `src/tools/chktrcmp.py'. 100 101 Each such component is assigned a `debug level', ranging from 0 to 102 7, through the use of the FT2_DEBUG environment variable 103 (described below) when a program linked with FreeType starts. 104 105 When FT_TRACE is called, its level is compared to the one of the 106 corresponding component. Messages with trace levels *higher* than 107 the corresponding component level are filtered and never printed. 108 109 This means that trace messages with level 0 are always printed, 110 those with level 2 are only printed when the component level is 111 *at least* 2. 112 113 The second parameter to FT_TRACE must contain parentheses and 114 correspond to a printf-like call, as in 115 116 FT_TRACE( 2, ( "your %s is not %s\n", "foo", "bar" ) ) 117 118 The shortcut macros FT_TRACE0, FT_TRACE1, FT_TRACE2, ..., 119 FT_TRACE7 can be used with constant level indices, and are much 120 cleaner to use, as in 121 122 FT_TRACE2(( "your %s is not %s\n", "foo", "bar" )); 123 124 125 III. Environment variables 126 -------------------------- 127 128 The following environment variables control debugging output and 129 behaviour of FreeType at runtime. 130 131 132 FT2_DEBUG 133 134 This variable is only used when FreeType is built with 135 FT_DEBUG_LEVEL_TRACE defined. It contains a list of component 136 level definitions, following this format: 137 138 component1:level1 component2:level2 component3:level3 ... 139 140 where `componentX' is the name of a tracing component, as defined 141 in `fttrace.h', but without the `trace_' prefix. `levelX' is the 142 corresponding level to use at runtime. 143 144 `any' is a special component name that will be interpreted as 145 `any/all components'. For example, the following definitions 146 147 set FT2_DEBUG=any:2 memory:5 io:4 (on Windows) 148 export FT2_DEBUG="any:2 memory:5 io:4" (on Linux with bash) 149 150 both stipulate that all components should have level 2, except for 151 the memory and io components which will be set to trace levels 5 152 and 4, respectively. 153 154 155 FT2_DEBUG_MEMORY 156 157 This environment variable, when defined, tells FreeType to use a 158 debugging memory manager that will track leaking memory blocks as 159 well as other common errors like double frees. It is also capable 160 of reporting _where_ the leaking blocks were allocated, which 161 considerably saves time when debugging new additions to the 162 library. 163 164 This code is only compiled when FreeType is built with the 165 FT_DEBUG_MEMORY macro #defined in `ftoption.h' though, it will be 166 ignored in other builds. 167 168 169 FT2_ALLOC_TOTAL_MAX 170 171 This variable is ignored if FT2_DEBUG_MEMORY is not defined. It 172 allows you to specify a maximum heap size for all memory 173 allocations performed by FreeType. This is very useful to test 174 the robustness of the font engine and programs that use it in 175 tight memory conditions. 176 177 If it is undefined, or if its value is not strictly positive, then 178 no allocation bounds are checked at runtime. 179 180 181 FT2_ALLOC_COUNT_MAX 182 183 This variable is ignored if FT2_DEBUG_MEMORY is not defined. It 184 allows you to specify a maximum number of memory allocations 185 performed by FreeType before returning the error 186 FT_Err_Out_Of_Memory. This is useful for debugging and testing 187 the engine's robustness. 188 189 If it is undefined, or if its value is not strictly positive, then 190 no allocation bounds are checked at runtime. 191 192 ------------------------------------------------------------------------ 193 194 Copyright 2002-2018 by 195 David Turner, Robert Wilhelm, and Werner Lemberg. 196 197 This file is part of the FreeType project, and may only be used, 198 modified, and distributed under the terms of the FreeType project 199 license, LICENSE.TXT. By continuing to use, modify, or distribute this 200 file you indicate that you have read the license and understand and 201 accept it fully. 202 203 204 --- end of DEBUG --- 205