Hi, Michael, Unit square is a 1x1 square. From this you can scale and shear to get any parallelogram. (and rotate of course) Once you have the map, I assume you can go from one parallelogram to another by transforms to and from the unit square.
Here's more from Thomas last year, especially look at his last reply in the thread: http://www.nabble.com/how-to-get-correct-render-transform-on-multiple-screens-td8749538.html If you are absolutely sure you will only scale and translate, and not rotate or shear, you can probably hack a solution from just one equation (because in the transforms, sx and sy will always be equal to each other, and shx and shy should always be zero). I experimented with printing out and multiplying some transforms from a standalone application and determined that: 1) CTM and viewing transform have the same values 2) ScreenCTM and [View transform]x[Rendering transform] are *almost* the same, sharing the same sx and sy but not tx and ty 3) ScreenCTM's tx and ty are related to [View]x[Render] by sctm_tx = (view_tx * render_sx) + render_tx ...same for _ty Not that I would ever recommend a hack ;-) The only way to be sure things won't break in the future is to go through the full math routine, butyou don't need me to tell you that. BTW, thanks for posting your AffineTransformUtil class a while ago, it's been a great help and saved me some drudge math work. Hope this is useful and not too off the mark... Dan Slater -------- Original Message -------- Subject: RE: Tracking changes to the rendering transform? From: "Bishop, Michael W. CONTR J9C880" <[EMAIL PROTECTED]> Date: Fri, October 03, 2008 12:31 pm To: <batik-users@xmlgraphics.apache.org> Hi Thomas, I'm following you most of the way with the basic concept. There are a couple things I'm confused about: parl_to_parl takes two double[] src and dst as arguments. The method maps one parallelogram to another, but why does each double[] have 6 points? What is being passed in here, a transform or a parallelogram? The rest of the code makes sense. You also say the approach is to build a matrix that maps a unit square to the edges of a parallelogram. What is a unit square? A square that encompasses the parallelogram, much like a traditional bounding box? I guess I'm still fuzzy on the overall concept. Good point that what the receiving client is getting is an "absolute" representation. It's not really a delta, it represents the current state, replacing whatever was there before. I wasn't thinking about it that way. Your explanation makes sense in the equation, but getting D* (applying the 3pt method) is where I'm lost. My method handles scaling, but yours handles everything, if I could figure out how to use it given three points. I'd be interested to see how this works and think it'd be useful. I made it through Ordinary Differential Equations in school, so I'm happy to finally be putting Linear Algebra and Trig to use in my career. Michael ________________________________ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: Fri 10/3/2008 10:54 AM To: batik-users@xmlgraphics.apache.org Cc: batik-users@xmlgraphics.apache.org Subject: RE: Tracking changes to the rendering transform? Hi Michael, "Bishop, Michael W. CONTR J9C880" <[EMAIL PROTECTED]> wrote on 10/03/2008 10:22:42 AM: > > Once the receiving client gets these three points, I'm not clear > on how to derive the transform from the three > > points. That's a math issue, not a Batik issue of course. > > OK, I've been thinking about this issue some. I think I have an > idea for translate/scale, but I'm not sure about other transform values. The best example I could find with google was the affine class from agg: https://svn.enthought.com/enthought/browser/trunk/src/lib/enthought/kiva/agg/agg-2.4/src/agg_trans_affine.cpp?rev=7913 It has parl_to_parl methods that map any parallelogram to another parallelogram. > Let's say the receiving client receives 3 points; A1 (upper-left), > A2 (upper-right), and A3 (lower-left). > The receiving client already has a JSVGCanvas with three points C1, C2, C3. The important thing about the three point approach is that you honestly don't care what the destination canavas was showing, all you want to do is map those three points to the corners of the client's window (I would ignore aspect ratio issues to start with, but the basic idea would be to modify the target canvas coordinates to account for aspect ratio differences). > I'm thinking that a translation is derived to translate C1 to A1. > Now both of the upper-left corners match. Now for X scale, you > calculate the distance between C1 and C2 and A1 and A2 and apply the > right scale multiple For Y, it's C1 and C3 and A1 and A3. This is correct and will handle scaling but see the example code as it will handle any rotation/skew as well. > I don't think you scale around the center; you scale around the > origin (C1). Correct. > What I'm not clear on now is the (unlikely) case of other transforms > such as rotation, skew, and shear. These should all just drop out of the above approach, that is what is so nice about it. > Am I even on the right track for starting to handle these changes? Yes, I think so, but trying to figure out how to derive the affine to map any three src points to three dest points isn't trivial unless you have a really good understanding of affine transforms. At some point I may try and write something for the wiki that explains how that 3pt mapping code works as it illustrates some useful ways of thinking about affine transforms. The basic approach is to build a matrix that maps a unit square to the edges of any parallelogram. Then you can use inverse and multiply to map between parallelograms. > From: Bishop, Michael W. CONTR J9C880 [mailto:[EMAIL PROTECTED] > Sent: Thu 10/2/2008 11:04 AM > To: batik-users@xmlgraphics.apache.org > Subject: RE: Tracking changes to the rendering transform? > > You aren't done yet... > > This is where I start to get confused. I have to remove the > existing VIEWING transform to derive the RENDERING transform? So I > "remove" the VIEWING transform by doing the inverse, then apply that > inverse to the RENDERING transform to get the final value? Right it's useful to view it this way: D = Display transform, goes from Root SVG elements coordinate system to screen pixels. V = Viewing transform, the transform established by the viewBox and window size. R = Rendering transform, the transform created by pan/zoom/rotate. V*R = D Using the 3pt method you will calculate a new D -> D'. So you want to calculate an R' such that: V*R' = D' The easiest way to do that is: inv(V)*V*R' = inv(V)*D' Which is the same as: R' = inv(V)*D' > > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > Sent: Tue 9/30/2008 9:21 PM > To: batik-users@xmlgraphics.apache.org > Cc: batik-users@xmlgraphics.apache.org > Subject: RE: Tracking changes to the rendering transform? > > > > Hi Michael, > > "Bishop, Michael W. CONTR J9C880" <[EMAIL PROTECTED]> > wrote on 09/25/2008 01:13:47 PM: > > > "The one thing you need to consider is that the rendering transform > > does interact with the viewing transform (From the viewbox). So in > > the case that the window that is viewing the document is a different > > size/aspect ratio then you may need a different rendering transform > > to get the same 'view'. " > > > > In a whiteboarding situation, the document is supposed to stay in > > sync between clients. Assuming that we are syncing changes to the > > viewBox attribute, does this satisfy the need to manage the > viewing transform? > > I don't think so... > > Since the rendering transform sits outside of the viewing transform > if one client has a window that is say 600 pixels wide and is paned over > so that the left edge is in the middle of the screen their translate > would be 300. However if that is applied to a Window that is 1200 > pixels wide the left edge would only be 1/4 of the way across. > > One way to view this problem is to communicate what points in > the root SVG element's coordinate system correspond to the corners > of the window. With that in mind it's worth noting that a general > affine transform can be specified by the remapping of three points > (e.g. top left, top right, and bottom left points that are visible > in the document). So you can easily calculate those points by > mapping the corners of the window to the root SVG element's coordinate > system (on change of the rendering transform). If you then send > those points to the other clients they can calculate the transform > that would map those same points to the corners of the new client's > window (probably with some adjustment for aspect ratio - which is > simple if you don't allow for non-uniform scaling). You aren't > done yet because that is the full transform and you need to remove > the existing viewing transform to know what the rendering transform > should be. Fortunately that is simply a matter of inverting the > viewing transform and multiplying/premultiplying that with the > 'full transform' to get the residual that should be set as the > rendering transform. > > I hope that this makes some sense to you. > > > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > > Sent: Thu 9/25/2008 6:34 AM > > To: batik-users@xmlgraphics.apache.org > > Cc: batik-users@xmlgraphics.apache.org > > Subject: RE: Tracking changes to the rendering transform? > > > > > > > > > > Hi Dan, Michael, > > > > "Dan Slater" <[EMAIL PROTECTED]> wrote on 09/23/2008 02:01:01 PM: > > > > > Extend the JSVGCanvas and override the setRenderingTransform method. > > > For example: > > > > Yes, this is how I would track changes to the rendering transform. > > We don't expose it through any of the Swing change API's. > > > > > public void setRenderingTransform(final AffineTransform at) { > > > //System.out.println("JSVGCanvasX set rendering > transform..."); > > > setRenderingTransform(at, true); > > > Point2D.Double pt2d = new Point2D. > > > Double(locationListener.getLastX(),locationListener.getLastY()); > > > SVGSVGElement root = this.getSVGDocument().getRootElement(); > > > if (root != null) setUserPositionXY(pt2d, root); > > > } > > > > "Bishop, Michael" <[EMAIL PROTECTED]> wrote on 09/23/2008: > > > > >> I'm in a whiteboarding situation where I want to communicate my > > >> "view" to other users. If I pan/zoom/etc, I want to be able to > > >> notify the other users as to what I'm looking at. I'm talking about > > >> view changes that do not modify the document. > > > > > >> I believe I can do this by tracking the render transform. Is there a > > >> way to listen for changes to the render transform? > > > > See above... > > > > >> Is there anything else I have to think about tracking to achieve > > >> this goal? I know the "viewBox" attribute exists, but that's > > >> different; it's a modification to the document itself. > > > > The one thing you need to consider is that the rendering transform > > does interact with the viewing transform (From the viewbox). So in > > the case that the window that is viewing the document is a different > > size/aspect ratio then you may need a different rendering transform > > to get the same 'view'. > > > > [attachment "winmail.dat" deleted by Thomas E. DeWeese/449433/EKC] > > --------------------------------------------------------------------- > > To unsubscribe, e-mail: [EMAIL PROTECTED] > > For additional commands, e-mail: [EMAIL PROTECTED] > [attachment "winmail.dat" deleted by Thomas E. DeWeese/449433/EKC] > --------------------------------------------------------------------- > To unsubscribe, e-mail: [EMAIL PROTECTED] > For additional commands, e-mail: [EMAIL PROTECTED] --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
