[Plplot-cvs] SF.net SVN: plplot: [7873] trunk/drivers/svg.c

[<ai...@us...>]

Revision: 7873
          http://plplot.svn.sourceforge.net/plplot/?rev=7873&view=rev
Author:   airwin
Date:     2007-09-18 11:24:47 -0700 (Tue, 18 Sep 2007)

Log Message:
-----------
Correct definitions of rotation and shear angles so this device gives
correct results for the 28th example. 

Modified Paths:
--------------
    trunk/drivers/svg.c

Modified: trunk/drivers/svg.c
===================================================================
--- trunk/drivers/svg.c	2007-09-18 17:44:26 UTC (rev 7872)
+++ trunk/drivers/svg.c	2007-09-18 18:24:47 UTC (rev 7873)
@@ -376,7 +376,7 @@
    short lastOffset = 0;
    double ftHt;
    PLUNICODE fci;
-   PLFLT rotation, shear, cos_rot, sin_rot, sin_shear;
+   PLFLT rotation, shear, cos_rot, sin_rot, sin_shear, cos_shear;
    PLFLT t[4];
    //   PLFLT *t = args->xform;
    PLUNICODE *ucs4 = args->unicode_array;
@@ -397,13 +397,17 @@
    // Calculate the tranformation matrix for SVG based on the
    // transformation matrix provived by PLplot.
    plRotationShear(args->xform, &rotation, &shear);
+   // N.B. Experimentally, I (AWI) have found the svg rotation angle is
+   // the negative of the libcairo rotation angle, and the svg shear angle
+   // is pi minus the libcairo shear angle.
    cos_rot = cos(rotation);
-   sin_rot = sin(rotation);
+   sin_rot = -sin(rotation);
    sin_shear = sin(shear);
+   cos_shear = -cos(shear);
    t[0] = cos_rot;
-   t[1] = sin_rot;
-   t[2] = sin_rot + cos_rot * sin_shear;
-   t[3] = -cos_rot + sin_rot * sin_shear;
+   t[1] = -sin_rot;
+   t[2] = cos_rot * sin_shear + sin_rot * cos_shear;
+   t[3] = -sin_rot * sin_shear + cos_rot * cos_shear;
 
    // Apply coordinate transform for text display.
    // The transformation also defines the location of the text in x and y.


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