David Turner | 02c3aed | 2002-07-08 23:02:32 +0000 | [diff] [blame^] | 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 builds. |
| 8 | This is controled through the definition of special macros located in the |
| 9 | 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 | used to print error messages during program execution. This will not |
| 16 | stop the program, but is very useful to spot invalid fonts during |
| 17 | development and code wordarounds for them. |
| 18 | |
| 19 | |
| 20 | FT_DEBUG_LEVEL_TRACE :: |
| 21 | |
| 22 | #define this macro if you want to compile both the FT_ERROR macro and |
| 23 | the FT_TRACE one. This also includes the variants FT_TRACE0, FT_TRACE1, |
| 24 | FT_TRACE2, ..., FT_TRACE6. |
| 25 | |
| 26 | The trace macros are used to send debugging messages when an appropriate |
| 27 | "debug level" is configured at runtime through the FT2_DEBUG environment |
| 28 | variable (more on this later) |
| 29 | |
| 30 | |
| 31 | FT_DEBUG_MEMORY :: |
| 32 | |
| 33 | when this macro is #defined, the FreeType engines is linked with a small |
| 34 | but effective debugging memory manager that tracks all allocations and |
| 35 | frees that are performed within the font engine. |
| 36 | |
| 37 | When the FT2_DEBUG_MEMORY environment variable is defined at runtime, a |
| 38 | call to FT_Done_FreeType will dump memory statistics, including the list of |
| 39 | leaked memory blocks with the source locations where these were allocated. |
| 40 | It's always a very good idea to define this in development builds. This |
| 41 | works with _any_ program linked to FreeType, but requires a big deal of |
| 42 | memory (the debugging memory manager never frees the blocks to the |
| 43 | heap in order to detect double frees). |
| 44 | |
| 45 | When FT2_DEBUG_MEMORY isn't defined at runtime, the debugging memory |
| 46 | manager is ignored, and performance is un-affected. |
| 47 | |
| 48 | |
| 49 | II. Debugging macros: |
| 50 | ===================== |
| 51 | |
| 52 | Several macros can be used within the FreeType sources to help debugging |
| 53 | its code: |
| 54 | |
| 55 | 1. FT_ERROR(( .. )) |
| 56 | |
| 57 | this macro is used to send debug messages that indicate relatively serious |
| 58 | errors (like broken font files), but will not stop the execution of the |
| 59 | running program. Its code is compiled only when either FT_DEBUG_LEVEL_ERROR |
| 60 | or FT_DEBUG_LEVEL_TRACE are defined in "ftoption.h" |
| 61 | |
| 62 | Note that you must use with a printf-like signature, but with double |
| 63 | parentheses, like in: |
| 64 | |
| 65 | FT_ERROR(( "your %s is not %s\n", "foo", "bar" )); |
| 66 | |
| 67 | |
| 68 | 2. FT_ASSERT( condition ) |
| 69 | |
| 70 | this macro is used to check strong assertions at runtime. If its condition |
| 71 | isn't TRUE, the program will abort with a panic message. Its code is |
| 72 | compiled when either FT_DEBUG_LEVEL_ERROR or FT_DEBUG_LEVEL_TRACE are |
| 73 | defined. You don't need double-parentheses here. For example: |
| 74 | |
| 75 | FT_ASSERT( ptr != NULL ); |
| 76 | |
| 77 | |
| 78 | 3. FT_TRACE( level, (message...) ) |
| 79 | |
| 80 | the FT_TRACE macro is used to send general-purpose debugging messages |
| 81 | during program execution. This macro uses an *implicit* macro named |
| 82 | FT_COMPONENT used to name the current FreeType component being run. |
| 83 | |
| 84 | The developer should always define FT_COMPONENT as appropriate, for |
| 85 | example as in: |
| 86 | |
| 87 | #undef FT_COMPONENT |
| 88 | #define FT_COMPONENT trace_io |
| 89 | |
| 90 | the value of the FT_COMPONENT macro is an enumeration named trace_XXXX |
| 91 | where XXXX is one of the component names defined in the internal file |
| 92 | <freetype/internal/fttrace.h> |
| 93 | |
| 94 | Each such component is assigned a "debug level", ranging from 0 to 6 |
| 95 | when a program linked with FreeType starts, through the use of the FT2_DEBUG |
| 96 | environment variable, described later. |
| 97 | |
| 98 | When FT_TRACE is called, its level is compared to the one of the |
| 99 | corresponding component. Messages with trace levels *higher* than the |
| 100 | corresponding component level are filtered and never printed. |
| 101 | |
| 102 | this means that trace messages with level 0 are always printed, those |
| 103 | with level 2 are only printed when the component level is *at least* 2 |
| 104 | |
| 105 | The second parameter to FT_TRACE must contain parentheses and correspond |
| 106 | to a print-like call, as in: |
| 107 | |
| 108 | FT_TRACE( 2, ( "your %s is not %s\n", "foo", "bar" ) ) |
| 109 | |
| 110 | The shortcut macros FT_TRACE0, FT_TRACE1, FT_TRACE2_, ... FT_TRACE6 can |
| 111 | be used with constant level indices, and are much cleaner to use, as in |
| 112 | |
| 113 | FT_TRACE2(( "your %s is not %s\n", "foo", "bar" )); |
| 114 | |
| 115 | |
| 116 | III. Environment variables: |
| 117 | =========================== |
| 118 | |
| 119 | The following environment variables control debugging output and behaviour |
| 120 | of FreeType at runtime: |
| 121 | |
| 122 | |
| 123 | FT2_DEBUG |
| 124 | this variable is only used when FreeType is built with FT_DEBUG_LEVEL_TRACE |
| 125 | defined. It contains a list of component level definitions, following this |
| 126 | format: |
| 127 | |
| 128 | component1:level1 component2:level2 component3:level3 ... |
| 129 | |
| 130 | where "componentX" is the name of a tracing component, as defined in |
| 131 | "fttrace.h", but without the "trace_" prefix, and "levelX" is the |
| 132 | corresponding level to use at runtime. |
| 133 | |
| 134 | "any" is a special component name that will be interpreted as |
| 135 | "any/all components". For example, the following definitions |
| 136 | |
| 137 | set FT2_DEBUG=any:2 memory:5 io:4 (on Windows) |
| 138 | export FT2_DEBUG="any:2 memory:5 io:4" (on Linux) |
| 139 | |
| 140 | both stipulate that all components should have level 2, except for the |
| 141 | memory and io components which will be set to trace levels 5 and 4 |
| 142 | respectively. |
| 143 | |
| 144 | |
| 145 | FT2_DEBUG_MEMORY |
| 146 | this environment variable, when defined, tells FreeType to use a debugging |
| 147 | memory manager that will track leaked memory blocks as well as other common |
| 148 | errors like double frees. It is also capable of reporting _where_ the |
| 149 | leaked blocks were allocated, which considerably saves time when |
| 150 | debugging new additions to the library. |
| 151 | |
| 152 | This code is only compiled when FreeType is built with the FT_DEBUG_MEMORY |
| 153 | macro #defined in "ftoption.h" though, it will be ignored in other builds. |
| 154 | |
| 155 | |
| 156 | Voila, |
| 157 | |
| 158 | - David Turner |
| 159 | |
| 160 | |
| 161 | |
| 162 | used like printf( format, ... ), but with double quotes. This will |
| 163 | send a message to the standard error descriptor (stderr on most systems) |
| 164 | in certain builds of the library |