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cmap [2020/02/23 10:28] christian [General Info] |
cmap [2020/02/23 14:26] christian [Char to string mapping] |
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| endbfrange | endbfrange | ||
| </ | </ | ||
| - | ===== Decoding ===== | ||
| - | The steps of decoding are: | ||
| - | * take the first byte from the source and find a 1-byte codespace range which includes it | ||
| - | * if found, find a 1-byte mapping for the byte | ||
| - | * if found, return the destination code or character | ||
| - | * if no mapping found, try to find a notdef mapping and return the code | ||
| - | * if not found, see below | ||
| - | * if not found, read the next byte and repeat with 2-byte mappings | ||
| - | |||
| - | When no mapping was found, one has to find out how many of the unmappable bytes have to be read from the source. This is not well defined (or I have not understood it yet). | ||
| ===== Implementation notes ===== | ===== Implementation notes ===== | ||
| Line 134: | Line 124: | ||
| * the mappings are ordered. This is not strictly prescribed, but recommended by the specifications. | * the mappings are ordered. This is not strictly prescribed, but recommended by the specifications. | ||
| - | ==== Handling malformed | + | ===== Monster from the wild ===== |
| + | |||
| + | CMaps are not well defined. Therefore, there are some interesting variations of them in the wild. Here is a small selection of some issues. | ||
| + | ==== Codespace problems ==== | ||
| + | |||
| + | === Wrong code length === | ||
| + | |||
| + | <code postscript> | ||
| + | %... | ||
| + | 1 begincodespacerange | ||
| + | < | ||
| + | endcodespacerange | ||
| + | 27 beginbfchar | ||
| + | <20> < | ||
| + | <2E> < | ||
| + | <43> < | ||
| + | <44> < | ||
| + | <45> < | ||
| + | %... | ||
| + | </ | ||
| + | |||
| + | Here are single byte mappings in a double byte codespace which is not correct according to the documentation. | ||
| + | |||
| + | This can be seen often. These illegal mappings are collected into the ''# | ||
| + | |||
| + | === Mappings outside the codespace === | ||
| + | |||
| + | <code postscript> | ||
| + | %... | ||
| + | 1 begincodespacerange | ||
| + | < | ||
| + | endcodespacerange | ||
| + | 11 beginbfchar | ||
| + | < | ||
| + | < | ||
| + | < | ||
| + | < | ||
| + | < | ||
| + | %... | ||
| + | </ | ||
| + | |||
| + | Here, only the first mapping matches the code space. All others fall outside of it, because the second byte has to be between <00> and < | ||
| + | |||
| + | ==== Wrong PostScript ==== | ||
| + | |||
| + | On one occasion, I saw a CMap where the PostScript used a non-existing operator (''/ | ||
| + | ==== Prevent copying | ||
| - | Sometimes CMaps define mappings which are not covered by the codespace ranges. This can be seen very often in the wild. These illegal mappings are collected into the ''# | + | <code postscript> |
| - | ===== Examples from the wild ===== | + | %... |
| + | 1 begincodespacerange | ||
| + | < | ||
| + | endcodespacerange | ||
| + | 100 beginbfchar | ||
| + | < | ||
| + | < | ||
| + | < | ||
| + | < | ||
| + | < | ||
| + | %... | ||
| + | < | ||
| + | < | ||
| + | < | ||
| + | < | ||
| + | < | ||
| + | < | ||
| + | < | ||
| + | %... | ||
| + | </ | ||
| - | single | + | Here, all codes map to the same character (Substitute character, Ctrl-Z) to prevent extracting the text. Interesting is also the ordering by the second |
| - | using /find instead of /findresource | + | Seen in [[https://github.com/ |
| + | ==== Char to string mapping ==== | ||
| - | preventing copying | + | <code postscript> |
| + | %... | ||
| + | /CMapType 2 def | ||
| + | 1 begincodespacerange | ||
| + | < | ||
| + | endcodespacerange | ||
| + | 1 beginbfchar | ||
| + | < | ||
| + | endbfchar | ||
| + | 1 beginbfchar | ||
| + | < | ||
| + | endbfchar | ||
| + | 50 beginbfrange | ||
| + | < | ||
| + | %... | ||
| + | </ | ||
| + | Two codes (<24> and <50>) are mapped to a string of 2-byte characters. This is defined by the PDF spec(({{pdf: | ||
| + | Seen in a PDF with the '' | ||