Getting text position while parsing pdf with Quartz 2D

Question

another question regarding pdf parsing... Just read PDF Reference version 1.7 "5.3.1 Text-Positioning Operators" and I am a little bit confused.

I wrote some code to get transformation matrix and initial text position.

        CGPDFOperatorTableSetCallback (table, "MP", &op_MP);//Define marked-content point
    CGPDFOperatorTableSetCallback (table, "DP", &op_DP);//Define marked-content point with property list
    CGPDFOperatorTableSetCallback (table, "BMC", &op_BMC);//Begin marked-content sequence
    CGPDFOperatorTableSetCallback (table, "BDC", &op_BDC);//Begin marked-content sequence with property list
    CGPDFOperatorTableSetCallback (table, "EMC", &op_EMC);//End marked-content sequence

    //Text State operators
    CGPDFOperatorTableSetCallback(table, "Tc", &op_Tc);
    CGPDFOperatorTableSetCallback(table, "Tw", &op_Tw);
    CGPDFOperatorTableSetCallback(table, "Tz", &op_Tz);
    CGPDFOperatorTableSetCallback(table, "TL", &op_TL);
    CGPDFOperatorTableSetCallback(table, "Tf", &op_Tf);
    CGPDFOperatorTableSetCallback(table, "Tr", &op_Tr);
    CGPDFOperatorTableSetCallback(table, "Ts", &op_Ts);

    //text showing operators
    CGPDFOperatorTableSetCallback(table, "TJ", &op_TJ);
    CGPDFOperatorTableSetCallback(table, "Tj", &op_Tj);
    CGPDFOperatorTableSetCallback(table, "'", &op_apostrof);
    CGPDFOperatorTableSetCallback(table, "\"", &op_double_apostrof);

    //text positioning operators        
    CGPDFOperatorTableSetCallback(table, "Td", &op_Td);
    CGPDFOperatorTableSetCallback(table, "TD", &op_TD);
    CGPDFOperatorTableSetCallback(table, "Tm", &op_Tm);
    CGPDFOperatorTableSetCallback(table, "T*", &op_T);

    //text object operators
    CGPDFOperatorTableSetCallback(table, "BT", &op_BT);//Begin text object
    CGPDFOperatorTableSetCallback(table, "ET", &op_ET);//End text object

So this is the output after application lunch:

    2010-09-02 15:09:23.041 testSearch[8251:207] op_BT begin
    Integer value: 0
    2010-09-02 15:09:23.043 testSearch[8251:207] op_BT end
    2010-09-02 15:09:23.043 testSearch[8251:207] op_Tf begin
    Integer value: 1
    2010-09-02 15:09:23.044 testSearch[8251:207] op_Tf end
    2010-09-02 15:09:23.044 testSearch[8251:207] op_Tm begin
    Float value: 557.364197
    2010-09-02 15:09:23.045 testSearch[8251:207] op_Tm end
    2010-09-02 15:09:23.045 testSearch[8251:207] op_TJ begin
    2010-09-02 15:09:23.046 testSearch[8251:207] Array string value [0]: F
    2010-09-02 15:09:23.046 testSearch[8251:207] Array integer value [1]: 94985208
    2010-09-02 15:09:23.047 testSearch[8251:207] Array string value [2]: r
    2010-09-02 15:09:23.047 testSearch[8251:207] Array integer value [3]: 94985208
    2010-09-02 15:09:23.048 testSearch[8251:207] Array string value [4]: o
    2010-09-02 15:09:23.048 testSearch[8251:207] Array integer value [5]: 94985208
    2010-09-02 15:09:23.049 testSearch[8251:207] Array string value [6]: m s
    2010-09-02 15:09:23.049 testSearch[8251:207] Array integer value [7]: 94985208
    2010-09-02 15:09:23.049 testSearch[8251:207] Array string value [8]: a
    2010-09-02 15:09:23.050 testSearch[8251:207] Array integer value [9]: 94985208
    2010-09-02 15:09:23.050 testSearch[8251:207] Array string value [10]: m
    2010-09-02 15:09:23.051 testSearch[8251:207] Array integer value [11]: 94985208
    2010-09-02 15:09:23.051 testSearch[8251:207] Array string value [12]: p
    2010-09-02 15:09:23.052 testSearch[8251:207] Array integer value [13]: 94985208
    2010-09-02 15:09:23.053 testSearch[8251:207] Array string value [14]: l
    2010-09-02 15:09:23.054 testSearch[8251:207] Array integer value [15]: 94985208
    2010-09-02 15:09:23.055 testSearch[8251:207] Array string value [16]: e t
    2010-09-02 15:09:23.055 testSearch[8251:207] Array integer value [17]: 94985208
    2010-09-02 15:09:23.057 testSearch[8251:207] Array string value [18]: o r
    2010-09-02 15:09:23.057 testSearch[8251:207] Array integer value [19]: 94985208
    2010-09-02 15:09:23.058 testSearch[8251:207] Array string value [20]: e
    2010-09-02 15:09:23.058 testSearch[8251:207] Array integer value [21]: 94985208
    2010-09-02 15:09:23.059 testSearch[8251:207] Array string value [22]: s
    2010-09-02 15:09:23.059 testSearch[8251:207] Array integer value [23]: 94985208
    2010-09-02 15:09:23.060 testSearch[8251:207] Array string value [24]: u
    2010-09-02 15:09:23.061 testSearch[8251:207] Array integer value [25]: 94985208
    2010-09-02 15:09:23.061 testSearch[8251:207] Array string value [26]: l
    2010-09-02 15:09:23.062 testSearch[8251:207] Array integer value [27]: 94985208
    2010-09-02 15:09:23.062 testSearch[8251:207] Array string value [28]: t
    2010-09-02 15:09:23.063 testSearch[8251:207] op_TJ end

If someone is familiar with text matrix and text positioning operators it would be nice to explain how all those thing work.

How to calculate text position (or glyph?) using Tm (transformation matrix and other data)?

Answer 1

@Koteg : Hi ! Have you finally managed to get it work ? For Tm, i'm able to get all the six values, but for now i can't see how to get the position of a word into a line ... I have an idea : if we are in Tj, just get the space between letters (hopping this the same everytime) and with Tm, get the position of a word. In the case of TJ, this is quite more complicated : get the value of horizontal translation to substract to Tm matrix for each part of the array, but searching a word in that array will be more complicated than for Tj.

BTW, for others people :

for(size_t n = 0; n < CGPDFArrayGetCount(array); n += 2)
{
    if(n >= CGPDFArrayGetCount(array))
        continue;

    CGPDFStringRef string;
    success = CGPDFArrayGetString(array, n, &string);
    if(success)
    {
        NSString *data = (NSString *)CGPDFStringCopyTextString(string);
        NSLog(@"array data : %@", data);

        [searcher.currentData appendFormat:@"%@", data];
        [data release];
    }

    CGPDFReal real;
    success = CGPDFArrayGetNumber(array, n+1, &real);
    if(success)
    {
        NSLog(@"array real : %f", real);
    }
}

Thanks