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1 Debugging within the FreeType sources |
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2 ===================================== |
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3 |
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4 I. Configuration macros |
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5 ----------------------- |
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6 |
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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 |
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11 |
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12 FT_DEBUG_LEVEL_ERROR |
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13 |
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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 |
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19 FT_DEBUG_LEVEL_TRACE |
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20 |
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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 |
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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 |
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29 FT_DEBUG_MEMORY |
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30 |
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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 |
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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 |
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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 |
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47 |
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48 II. Debugging macros |
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49 -------------------- |
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50 |
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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 |
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54 |
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55 1. FT_ERROR(( ... )) |
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56 |
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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 |
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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 |
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66 FT_ERROR(( "your %s is not %s\n", "foo", "bar" )); |
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67 |
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68 |
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69 2. FT_ASSERT( condition ) |
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70 |
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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 |
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77 FT_ASSERT( ptr != NULL ); |
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78 |
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79 |
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80 3. FT_TRACE( level, (message...) ) |
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81 |
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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 |
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87 The developer should always define FT_COMPONENT as appropriate, for |
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88 example as in |
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89 |
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90 #undef FT_COMPONENT |
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91 #define FT_COMPONENT trace_io |
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92 |
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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 |
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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 |
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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 |
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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 |
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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 |
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115 FT_TRACE( 2, ( "your %s is not %s\n", "foo", "bar" ) ) |
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116 |
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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 |
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121 FT_TRACE2(( "your %s is not %s\n", "foo", "bar" )); |
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122 |
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123 |
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124 III. Environment variables |
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125 -------------------------- |
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126 |
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127 The following environment variables control debugging output and |
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128 behaviour of FreeType at runtime. |
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129 |
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130 |
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131 FT2_DEBUG |
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132 |
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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 |
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137 component1:level1 component2:level2 component3:level3 ... |
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138 |
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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 |
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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 |
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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 |
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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 |
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153 |
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154 FT2_DEBUG_MEMORY |
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155 |
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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 |
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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 |
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166 |
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167 FT2_ALLOC_TOTAL_MAX |
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168 |
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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 |
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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 |
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178 |
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179 FT2_ALLOC_COUNT_MAX |
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180 |
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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 |
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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 |
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190 ------------------------------------------------------------------------ |
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191 |
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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 |
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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 |
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201 |
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202 --- end of DEBUG --- |