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cmap [2020/02/23 11:11] christian [Prevent copying] |
cmap [2020/02/23 14:33] (current) christian [CMap] |
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| ====== CMap ====== | ====== CMap ====== | ||
| - | CMaps(([[https:// | + | CMaps(([[https:// |
| CMaps provide a very general mechanism which can describe any mappings, including unicode which was developed later. Input codes of variable length (1, 2, 3 or more bytes) can be mapped to characters. | CMaps provide a very general mechanism which can describe any mappings, including unicode which was developed later. Input codes of variable length (1, 2, 3 or more bytes) can be mapped to characters. | ||
| Line 124: | 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 CMaps ==== | ||
| - | |||
| - | 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 ''# | ||
| ===== Monster from the wild ===== | ===== Monster from the wild ===== | ||
| - | ==== Mappings outside the codespace | + | 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 | ||
| - | single byte mappings in a double byte codespace | + | === Wrong code length === |
| - | ==== Wrong PostScript ==== | + | <code postscript> |
| + | %... | ||
| + | 1 begincodespacerange | ||
| + | < | ||
| + | endcodespacerange | ||
| + | 27 beginbfchar | ||
| + | <20> < | ||
| + | <2E> < | ||
| + | <43> < | ||
| + | <44> < | ||
| + | <45> < | ||
| + | %... | ||
| + | </ | ||
| - | using /find instead of / | + | 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 <04>. | ||
| + | |||
| + | ==== Wrong PostScript ==== | ||
| + | |||
| + | On one occasion, I saw a CMap where the PostScript used a non-existing operator (''/ | ||
| ==== Prevent copying ==== | ==== Prevent copying ==== | ||
| Line 163: | Line 196: | ||
| 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 byte, which forced me to redesign the object structure to avoid exponential processing time. | 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 byte, which forced me to redesign the object structure to avoid exponential processing time. | ||
| - | Seen in [[https:// | + | Seen in [[https:// |
| ==== Char to string mapping ==== | ==== Char to string mapping ==== | ||
| Line 183: | Line 216: | ||
| </ | </ | ||
| - | It looks as if two codes (<24> and <50>) are mapped to a string of 2-byte characters. | + | Two codes (<24> and <50>) are mapped to a string of 2-byte characters. |
| + | |||
| + | Seen in a PDF with the '' | ||