| | <<<Back 1 day (to 2021/02/24) | Fwd 1 day (to 2021/02/26)>>> | 20210225 |
| pedr0 | hi all - forgive me if I am saying silly things. I am struggling to translate an overlay that I drawing on the rendered image of a page into its page's coordinates. This is because the page is rotated via its page dictionary, what I do is to inject an instruction which defines a clipping area, but coordinates are totally wrong when pages are rotated. | 11:48.21 |
| | One of the many questions I've is: is it possible to 'embed' the rotation of the whole page within the stream of the page and get rid of the page dictionary /Rotate entry ? I don't think so as all coordinates after such instruction would be relative to another coordinate space. am I talking complete rubbish ? | 11:51.46 |
| artifexirc-bot | <Robin_Watts> pedr0: Yes, it's possible to embed the rotation of the whole page within the stream of the page. | 11:56.19 |
| | <Robin_Watts> How much do you know about PDF page streams? | 11:56.36 |
| pedr0 | I understand cm, rotation and translation, skew and T[jJ] - but the former more in theory than in practice as I never had to do anything like that | 11:57.43 |
| | I did try to insert a cm rotation operation, but it ruined the whole page and my understanding was that all what followed was referring to the wrong 'space' | 11:58.21 |
| | I read the specs a lot of times :-) | 11:58.38 |
| artifexirc-bot | <Robin_Watts> Right. So there is a 'current transformation matrix' (ctm) that maps from the space stuff is described in, to the actual pixels on the device. | 11:58.46 |
| | <ator> could you be looking at something ilke this maybe? "q <rotation matrix> cm <original contents> Q <non-rotated extras>" | 11:59.21 |
| | <Robin_Watts> Page contents can't ever 'set' that ctm, they can only modify it (using the cm instruction) | 11:59.26 |
| | <Robin_Watts> What @ator says is exactly what you need. | 11:59.56 |
| | <Robin_Watts> q stores the current state, and Q restores it. | 12:00.28 |
| pedr0 | The fact is that I want to rotate the whole thing - and get rid of the entry in the dictionary. | 12:00.34 |
| | I tried and did not work, let me try again | 12:00.44 |
| artifexirc-bot | <Robin_Watts> So, assuming your page contents are well formed (i.e. that the q and Q's match up), you can just modify the cm at the top level, and that will affect everything underneath it. | 12:01.21 |
| pedr0 | at the end I want the same page as before being rendered with the only exception that the /Rotate entry isn't there any longer | 12:01.22 |
| artifexirc-bot | <Robin_Watts> Basically, all the /Rotate entry does is to modify the initial ctm we pass in, so this approach WILL work. | 12:01.51 |
| pedr0 | Right | 12:02.00 |
| artifexirc-bot | <Robin_Watts> It's just that modification will happen within the page, rather than outside it. | 12:02.11 |
| pedr0 | That was my first hunch, I must have got lost somewhere while doing it, thanks *a lot* for that. | 12:02.32 |
| artifexirc-bot | <Robin_Watts> The one wrinkle in doing this generically is that some pages may have unbalanced q and Q operations. | 12:02.43 |
| | <KenSharp> @Robin_Watts the /Rotate also modifies the MediaBox..... | 12:03.01 |
| | <Robin_Watts> But you can solve that by 'sanitising' the stream. | 12:03.10 |
| | <KenSharp> Or is applied to the MediaBox or CropBox I should probably say | 12:03.16 |
| | <Robin_Watts> @KenSharp Right, yes. | 12:03.19 |
| | <KenSharp> So when removing teh /Rotate key from the /Page dictionary, you would need to alter teh MediaBox/CropBox/ArtBox/BleedBox.... | 12:04.03 |
| pedr0 | that's why I got an empty page when I tried maybe - did not notice that the MediaBox needed adjustment | 12:05.42 |
| | will keep you posted, thank you all | 12:05.53 |
| artifexirc-bot | <KenSharp> Ah, you will also need to translate the current point | 12:10.28 |
| pedr0 | what's that ? | 12:11.53 |
| | my stream started with [q ...] and I've prepended [q | 12:12.48 |
| | 0 -1 1 0 0 0 cm | 12:12.48 |
| | ] and got rid of the rotate entry | 12:12.48 |
| | changed the media box - and I get a blank page | 12:13.35 |
| artifexirc-bot | <KenSharp> Sorry, wasn't paying attention.... | 12:20.38 |
| | <KenSharp> Actually if you rotate the MediaBox you probably don't need to worry about the current point. | 12:20.57 |
| | <KenSharp> But if you rotate the content or the media independently of each other then you do. | 12:21.12 |
| artifexirc-bot | <KenSharp> reconsiders that | 12:21.51 |
| | <KenSharp> /Rotate (IIRC) rotates clockwise, I think you haev rotated the content anti-clockwise | 12:22.13 |
| | <KenSharp> In PDF 0,0 is the bottom left hand corner. If you rotate the CTM then the origin doesn't move. | 12:23.09 |
| | <KenSharp> The content rotates around the origin | 12:23.22 |
| | <KenSharp> So after you have done the rotate, you need to shift the origin so that it is at the bottom left again | 12:23.58 |
| | <KenSharp> Take a piece of A4, portrai. | 12:24.18 |
| | <KenSharp> Hold the bottom left coner, an rotate it by 90 degrees | 12:24.30 |
| | <KenSharp> You'll notice that the 'content' is now below the baselin and so falls off | 12:25.18 |
| | <KenSharp> So you need to shift the whole content up by the 'width' of the original page | 12:25.34 |
| | <KenSharp> Does thia make any sense ? | 12:25.39 |
| artifexirc-bot | <KenSharp> lunches | 12:27.31 |
| pedr0 | yes - but how do I shift the origin ? | 12:29.12 |
| | I see, with another cm | 12:29.29 |
| artifexirc-bot | <Robin_Watts> Or the same cm, just change the last 2 numbers. | 12:30.55 |
| | <KenSharp> Back. Yes what Robin said | 12:56.37 |
| pedr0 | It works, thank you all! | 13:02.50 |
| artifexirc-bot | <KenSharp> Ah good, glad it worked! | 13:04.47 |
| pedr0 | I've learned a few things along the way too | 13:06.33 |
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