Text chunks getting positions as in html?

Question

transform pdf points to pixels, worked correctly: point-to-pixel = 1/72*300(DPI)

1. getting each text chunk positions (X,Y) in PDF the Y is calculated from
   bottom-to-top, not as in standard html or java Script.
2. to get the Y value from top-to-down , cause not accurate Y position as in
   html style , or win Form style.

3. how to get the correct Y top-to-down using any Page height, or rect mediaBox
   or cropBox or rect textMarging finder ?

4. the code I used is your example of :

   public class LocationTextExtractionStrategyClass : LocationTextExtractionStrategy
   {
       //Hold each coordinate
       public List<RectAndText> myPoints = new List<RectAndText>();
       /*
       //The string that we're searching for
       public String TextToSearchFor { get; set; }
   
       //How to compare strings
       public System.Globalization.CompareOptions CompareOptions { get; set; }
   
       public MyLocationTextExtractionStrategy(String textToSearchFor, System.Globalization.CompareOptions compareOptions = System.Globalization.CompareOptions.None)
       {
           this.TextToSearchFor = textToSearchFor;
           this.CompareOptions = compareOptions;
       }
       */
       //Automatically called for each chunk of text in the PDF
       public override void RenderText(TextRenderInfo renderInfo)
       {
           base.RenderText(renderInfo);
   
           //See if the current chunk contains the text
           var startPosition = 0;// System.Globalization.CultureInfo.CurrentCulture.CompareInfo.IndexOf(renderInfo.GetText(), this.TextToSearchFor, this.CompareOptions);
   
           //If not found bail
           if (startPosition < 0)
           {
               return;
           }
   
           //Grab the individual characters
           var chars = renderInfo.GetCharacterRenderInfos().ToList();//.Skip(startPosition).Take(this.TextToSearchFor.Length)
           var charsText = renderInfo.GetText();
   
           //Grab the first and last character
           var firstChar = chars.First();
           var lastChar  = chars.Last();
   
           //Get the bounding box for the chunk of text
           var bottomLeft = firstChar.GetDescentLine().GetStartPoint();
           var topRight   = lastChar.GetAscentLine().GetEndPoint();
   
           //Create a rectangle from it
           var rect = new iTextSharp.text.Rectangle(
                                                   bottomLeft[Vector.I1],
                                                   bottomLeft[Vector.I2],
                                                   topRight[Vector.I1],
                                                   topRight[Vector.I2]
                                                   );
   
           BaseColor curColor = new BaseColor(0f, 0f, 0f);
           if (renderInfo.GetFillColor() != null)
               curColor = renderInfo.GetFillColor();
   
           //Add this to our main collection
           myPoints.Add(new RectAndText(rect, charsText, curColor));//this.TextToSearchFor));
       }
   }//end-of-txtLocation-class//
   

Answer 1

You are asking many different questions in one post.

First let's start with the coordinate system in the PDF standard. Observe that I am talking about a standard, more specifically about ISO 32000. The coordinate system on a PDF page is explained in my answer to the Stack Overflow question How should I interpret the coordinates of a rectangle in PDF?

As you can see, a rectangle drawn in a PDF using a coordinate (llx, lly) for the lower-left corner and a coordinate (urx, ury) for the upper-right corner, assumes that the X-axis points to the right, and the Y-axis points upwards.

As for the width and the height of a page, that's explained in my answer to the Stack Overflow question How to Get PDF page width and Height?

For instance: you could have a /MediaBox that is defined as [0 0 595 842], and therefore measures 595 x 842 points (an A4 page), but that has a /CropBox that is defined as [5 5 590 837], which means that the visible area is only 585 x 832 points.

You also shouldn't assume that the lower-left corner of a page coincides with the (0, 0) coordinate. See Where is the Origin (x,y) of a PDF page?

When you create a document from scratch, a default margin of half an inch is used if you don't define a margin yourself. If you want to change the default, see Fit content on pdf size with iTextSharp?

Now for the height of a Chunk or, if you're using iText 7 (which you should, but —for some reason unknown to me— don't) the height of a Text object, this depends on the font size. The font size is an average size of the different glyphs in a font. If you look at the letter g, and you compare it with the letter h, you see that g takes more space under the baseline of the text than h, whereas h takes more space above the baseline than g.

If you want to calculate the exact space that is taken, read my answer to the question How to calculate the height of an element?

If the text snippet is used in the context of lines in a paragraph, you also have to take the leading into account: Changing text line spacing (Maybe that's not relevant in the context of your question, but it's good to know.)

If you have Chunk objects in iText 5, and you want to do specific things with these Chunks, you might benefit from using page events. See How to draw a line every 25 words?

If you want to add a colored background to a Chunk, it's even easier: How to set the paragraph of itext pdf file as rectangle with background color in Java

Update 1: All of the above may be irrelevant if you are looking to convert HTML to PDF. In that case, it's easy: use iText 7 + pdfHTML as described in Converting HTML to PDF using iText and all the Math is done by the pdfHTML add-on.

Update 2: There seems to be some confusion regarding the measurement units. The differences between user units, points and pixels is explained in the FAQ page How do the measurement systems in HTML relate to the measurement system in PDF?

Summarized:

1 in. = 25.4 mm = 72 user units by default (but it can be changed).
1 in. = 25.4 mm = 72 pt.
1 in. = 25.4 mm = 96 px.