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cmap [2020/02/23 10:28] christian [General Info] |
cmap [2020/02/23 11:17] christian [Mappings outside the codespace] |
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| Line 108: | Line 108: | ||
| 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 CMaps ==== | + | ===== Monster from the wild ===== |
| - | 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 ''# | + | |
| - | ===== Examples from the wild ===== | + | ==== Mappings outside |
| single byte mappings in a double byte codespace | single byte mappings in a double byte codespace | ||
| - | using /find instead of / | + | 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 ''# |
| + | |||
| + | ==== Wrong PostScript ==== | ||
| + | |||
| + | using /find instead of / | ||
| + | |||
| + | See [[postscript# | ||
| + | ==== Prevent copying ==== | ||
| + | |||
| + | <code postscript> | ||
| + | %... | ||
| + | 1 begincodespacerange | ||
| + | < | ||
| + | endcodespacerange | ||
| + | 100 beginbfchar | ||
| + | < | ||
| + | < | ||
| + | < | ||
| + | < | ||
| + | < | ||
| + | %... | ||
| + | < | ||
| + | < | ||
| + | < | ||
| + | < | ||
| + | < | ||
| + | < | ||
| + | < | ||
| + | %... | ||
| + | </ | ||
| + | |||
| + | 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. | ||
| - | preventing copying | + | Seen in [[https:// |
| + | ==== Char to string mapping ==== | ||
| + | <code postscript> | ||
| + | %... | ||
| + | /CMapType 2 def | ||
| + | 1 begincodespacerange | ||
| + | < | ||
| + | endcodespacerange | ||
| + | 1 beginbfchar | ||
| + | < | ||
| + | endbfchar | ||
| + | 1 beginbfchar | ||
| + | < | ||
| + | endbfchar | ||
| + | 50 beginbfrange | ||
| + | < | ||
| + | %... | ||
| + | </ | ||
| + | It looks as if two codes (<24> and <50>) are mapped to a string of 2-byte characters. I have not found anything about this in the documenation. Seen in a PDF with the '' | ||