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4349 | Serge | 1 | Debugging within the FreeType sources |
2 | ===================================== |
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3 | |||
4 | I. Configuration macros |
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5 | ----------------------- |
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6 | |||
7 | There are several ways to enable debugging features in a FreeType 2 |
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8 | builds. This is controlled through the definition of special macros |
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9 | located in the file `ftoptions.h'. The macros are: |
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10 | |||
11 | |||
12 | FT_DEBUG_LEVEL_ERROR |
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13 | |||
14 | #define this macro if you want to compile the FT_ERROR macro calls |
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15 | to print error messages during program execution. This will not |
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16 | stop the program. Very useful to spot invalid fonts during |
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17 | development and to code workarounds for them. |
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18 | |||
19 | FT_DEBUG_LEVEL_TRACE |
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20 | |||
21 | #define this macro if you want to compile both macros FT_ERROR and |
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22 | FT_TRACE. This also includes the variants FT_TRACE0, FT_TRACE1, |
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23 | FT_TRACE2, ..., FT_TRACE7. |
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24 | |||
25 | The trace macros are used to send debugging messages when an |
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26 | appropriate `debug level' is configured at runtime through the |
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27 | FT2_DEBUG environment variable (more on this later). |
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28 | |||
29 | FT_DEBUG_MEMORY |
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30 | |||
31 | If this macro is #defined, the FreeType engine is linked with a |
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32 | small but effective debugging memory manager that tracks all |
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33 | allocations and frees that are performed within the font engine. |
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34 | |||
35 | When the FT2_DEBUG_MEMORY environment variable is defined at |
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36 | runtime, a call to FT_Done_FreeType will dump memory statistics, |
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37 | including the list of leaked memory blocks with the source locations |
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38 | where these were allocated. It is always a very good idea to define |
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39 | this in development builds. This works with _any_ program linked to |
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40 | FreeType, but requires a big deal of memory (the debugging memory |
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41 | manager never frees the blocks to the heap in order to detect double |
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42 | frees). |
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43 | |||
44 | When FT2_DEBUG_MEMORY isn't defined at runtime, the debugging memory |
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45 | manager is ignored, and performance is unaffected. |
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46 | |||
47 | |||
48 | II. Debugging macros |
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49 | -------------------- |
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50 | |||
51 | Several macros can be used within the FreeType sources to help debugging |
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52 | its code: |
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53 | |||
54 | |||
55 | 1. FT_ERROR(( ... )) |
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56 | |||
57 | This macro is used to send debug messages that indicate relatively |
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58 | serious errors (like broken font files), but will not stop the |
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59 | execution of the running program. Its code is compiled only when |
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60 | either FT_DEBUG_LEVEL_ERROR or FT_DEBUG_LEVEL_TRACE are defined in |
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61 | `ftoption.h'. |
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62 | |||
63 | Note that you have to use a printf-like signature, but with double |
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64 | parentheses, like in |
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65 | |||
66 | FT_ERROR(( "your %s is not %s\n", "foo", "bar" )); |
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67 | |||
68 | |||
69 | 2. FT_ASSERT( condition ) |
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70 | |||
71 | This macro is used to check strong assertions at runtime. If its |
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72 | condition isn't TRUE, the program will abort with a panic message. |
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73 | Its code is compiled when either FT_DEBUG_LEVEL_ERROR or |
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74 | FT_DEBUG_LEVEL_TRACE are defined. You don't need double parentheses |
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75 | here. For example |
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76 | |||
77 | FT_ASSERT( ptr != NULL ); |
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78 | |||
79 | |||
80 | 3. FT_TRACE( level, (message...) ) |
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81 | |||
82 | The FT_TRACE macro is used to send general-purpose debugging |
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83 | messages during program execution. This macro uses an *implicit* |
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84 | macro named FT_COMPONENT used to name the current FreeType component |
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85 | being run. |
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86 | |||
87 | The developer should always define FT_COMPONENT as appropriate, for |
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88 | example as in |
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89 | |||
90 | #undef FT_COMPONENT |
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91 | #define FT_COMPONENT trace_io |
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92 | |||
93 | The value of the FT_COMPONENT macro is an enumeration named |
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94 | trace_XXXX where XXXX is one of the component names defined in the |
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95 | internal file `freetype/internal/fttrace.h'. If you modify FreeType |
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96 | source and insert new trace_XXXX macro, you must register it in |
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97 | fttrace.h. If you insert or remove many trace macros, you can check |
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98 | the undefined or the unused trace macro by src/tools/chktrcmp.py. |
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99 | |||
100 | Each such component is assigned a `debug level', ranging from 0 |
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101 | to 7, through the use of the FT2_DEBUG environment variable |
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102 | (described below) when a program linked with FreeType starts. |
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103 | |||
104 | When FT_TRACE is called, its level is compared to the one of the |
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105 | corresponding component. Messages with trace levels *higher* than |
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106 | the corresponding component level are filtered and never printed. |
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107 | |||
108 | This means that trace messages with level 0 are always printed, |
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109 | those with level 2 are only printed when the component level is *at |
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110 | least* 2. |
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111 | |||
112 | The second parameter to FT_TRACE must contain parentheses and |
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113 | correspond to a printf-like call, as in |
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114 | |||
115 | FT_TRACE( 2, ( "your %s is not %s\n", "foo", "bar" ) ) |
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116 | |||
117 | The shortcut macros FT_TRACE0, FT_TRACE1, FT_TRACE2, ..., FT_TRACE7 |
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118 | can be used with constant level indices, and are much cleaner to |
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119 | use, as in |
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120 | |||
121 | FT_TRACE2(( "your %s is not %s\n", "foo", "bar" )); |
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122 | |||
123 | |||
124 | III. Environment variables |
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125 | -------------------------- |
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126 | |||
127 | The following environment variables control debugging output and |
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128 | behaviour of FreeType at runtime. |
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129 | |||
130 | |||
131 | FT2_DEBUG |
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132 | |||
133 | This variable is only used when FreeType is built with |
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134 | FT_DEBUG_LEVEL_TRACE defined. It contains a list of component level |
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135 | definitions, following this format: |
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136 | |||
137 | component1:level1 component2:level2 component3:level3 ... |
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138 | |||
139 | where `componentX' is the name of a tracing component, as defined in |
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140 | `fttrace.h', but without the `trace_' prefix. `levelX' is the |
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141 | corresponding level to use at runtime. |
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142 | |||
143 | `any' is a special component name that will be interpreted as |
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144 | `any/all components'. For example, the following definitions |
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145 | |||
146 | set FT2_DEBUG=any:2 memory:5 io:4 (on Windows) |
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147 | export FT2_DEBUG="any:2 memory:5 io:4" (on Linux with bash) |
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148 | |||
149 | both stipulate that all components should have level 2, except for |
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150 | the memory and io components which will be set to trace levels 5 and |
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151 | 4, respectively. |
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152 | |||
153 | |||
154 | FT2_DEBUG_MEMORY |
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155 | |||
156 | This environment variable, when defined, tells FreeType to use a |
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157 | debugging memory manager that will track leaking memory blocks as |
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158 | well as other common errors like double frees. It is also capable |
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159 | of reporting _where_ the leaking blocks were allocated, which |
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160 | considerably saves time when debugging new additions to the library. |
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161 | |||
162 | This code is only compiled when FreeType is built with the |
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163 | FT_DEBUG_MEMORY macro #defined in `ftoption.h' though, it will be |
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164 | ignored in other builds. |
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165 | |||
166 | |||
167 | FT2_ALLOC_TOTAL_MAX |
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168 | |||
169 | This variable is ignored if FT2_DEBUG_MEMORY is not defined. It |
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170 | allows you to specify a maximum heap size for all memory allocations |
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171 | performed by FreeType. This is very useful to test the robustness |
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172 | of the font engine and programs that use it in tight memory |
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173 | conditions. |
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174 | |||
175 | If it is undefined, or if its value is not strictly positive, then |
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176 | no allocation bounds are checked at runtime. |
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177 | |||
178 | |||
179 | FT2_ALLOC_COUNT_MAX |
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180 | |||
181 | This variable is ignored if FT2_DEBUG_MEMORY is not defined. It |
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182 | allows you to specify a maximum number of memory allocations |
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183 | performed by FreeType before returning the error |
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184 | FT_Err_Out_Of_Memory. This is useful for debugging and testing the |
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185 | engine's robustness. |
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186 | |||
187 | If it is undefined, or if its value is not strictly positive, then |
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188 | no allocation bounds are checked at runtime. |
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189 | |||
190 | ------------------------------------------------------------------------ |
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191 | |||
192 | Copyright 2002, 2003, 2004, 2005, 2009 by |
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193 | David Turner, Robert Wilhelm, and Werner Lemberg. |
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194 | |||
195 | This file is part of the FreeType project, and may only be used, |
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196 | modified, and distributed under the terms of the FreeType project |
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197 | license, LICENSE.TXT. By continuing to use, modify, or distribute this |
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198 | file you indicate that you have read the license and understand and |
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199 | accept it fully. |
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200 | |||
201 | |||
202 | --- end of DEBUG --- |