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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 `ftoptions.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 locations
38 where these were allocated. It is always a very good idea to define
39 this in development builds. This works with _any_ program linked to
40 FreeType, but requires a big deal of memory (the debugging memory
41 manager never frees the blocks to the heap in order to detect double
42 frees).
43
44 When FT2_DEBUG_MEMORY isn't defined at runtime, the debugging memory
45 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 debugging
52 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 parentheses
75 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 component
85 being run.
86
87 The developer should always define FT_COMPONENT as appropriate, for
88 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 the
95 internal file `freetype/internal/fttrace.h'.
96
97 Each such component is assigned a `debug level', ranging from 0
98 to 7, through the use of the FT2_DEBUG environment variable
99 (described below) when a program linked with FreeType starts.
100
101 When FT_TRACE is called, its level is compared to the one of the
102 corresponding component. Messages with trace levels *higher* than
103 the corresponding component level are filtered and never printed.
104
105 This means that trace messages with level 0 are always printed,
106 those with level 2 are only printed when the component level is *at
107 least* 2.
108
109 The second parameter to FT_TRACE must contain parentheses and
110 correspond to a printf-like call, as in
111
112 FT_TRACE( 2, ( "your %s is not %s\n", "foo", "bar" ) )
113
114 The shortcut macros FT_TRACE0, FT_TRACE1, FT_TRACE2, ..., FT_TRACE7
115 can be used with constant level indices, and are much cleaner to
116 use, as in
117
118 FT_TRACE2(( "your %s is not %s\n", "foo", "bar" ));
119
120
121 III. Environment variables
122 --------------------------
123
124 The following environment variables control debugging output and
125 behaviour of FreeType at runtime.
126
127
128 FT2_DEBUG
129
130 This variable is only used when FreeType is built with
131 FT_DEBUG_LEVEL_TRACE defined. It contains a list of component level
132 definitions, following this format:
133
134 component1:level1 component2:level2 component3:level3 ...
135
136 where `componentX' is the name of a tracing component, as defined in
137 `fttrace.h', but without the `trace_' prefix. `levelX' is the
138 corresponding level to use at runtime.
139
140 `any' is a special component name that will be interpreted as
141 `any/all components'. For example, the following definitions
142
143 set FT2_DEBUG=any:2 memory:5 io:4 (on Windows)
144 export FT2_DEBUG="any:2 memory:5 io:4" (on Linux with bash)
145
146 both stipulate that all components should have level 2, except for
147 the memory and io components which will be set to trace levels 5 and
148 4, respectively.
149
150
151 FT2_DEBUG_MEMORY
152
153 This environment variable, when defined, tells FreeType to use a
154 debugging memory manager that will track leaking memory blocks as
155 well as other common errors like double frees. It is also capable
156 of reporting _where_ the leaking blocks were allocated, which
157 considerably saves time when debugging new additions to the library.
158
159 This code is only compiled when FreeType is built with the
160 FT_DEBUG_MEMORY macro #defined in `ftoption.h' though, it will be
161 ignored in other builds.
162
163
164 FT2_ALLOC_TOTAL_MAX
165
166 This variable is ignored if FT2_DEBUG_MEMORY is not defined. It
167 allows you to specify a maximum heap size for all memory allocations
168 performed by FreeType. This is very useful to test the robustness
169 of the font engine and programs that use it in tight memory
170 conditions.
171
172 If it is undefined, or if its value is not strictly positive, then
173 no allocation bounds are checked at runtime.
174
175
176 FT2_ALLOC_COUNT_MAX
177
178 This variable is ignored if FT2_DEBUG_MEMORY is not defined. It
179 allows you to specify a maximum number of memory allocations
180 performed by FreeType before returning the error
181 FT_Err_Out_Of_Memory. This is useful for debugging and testing the
182 engine's robustness.
183
184 If it is undefined, or if its value is not strictly positive, then
185 no allocation bounds are checked at runtime.
186
187 ------------------------------------------------------------------------
188
189 Copyright 2002, 2003, 2004, 2005 by
190 David Turner, Robert Wilhelm, and Werner Lemberg.
191
192 This file is part of the FreeType project, and may only be used,
193 modified, and distributed under the terms of the FreeType project
194 license, LICENSE.TXT. By continuing to use, modify, or distribute this
195 file you indicate that you have read the license and understand and
196 accept it fully.
197
198
199 --- end of DEBUG ---