Add special rotation solution to optimized transforms, found by Johan

(bzr r13691)

2 files changed, 13 insertions, 12 deletions

diff --git a/src/svg/svg-affine-test.h b/src/svg/svg-affine-test.h
index 6d8387328..af670a3a8 100644
--- a/src/svg/svg-affine-test.h
+++ b/src/svg/svg-affine-test.h
@@ -35,7 +35,7 @@ private:
     static test_t const write_matrix_tests[2];
     static test_t const write_translate_tests[3];
     static test_t const write_scale_tests[3];
-    static test_t const write_rotate_tests[2];
+    static test_t const write_rotate_tests[3];
     static test_t const write_skew_tests[3];
 public:
     SvgAffineTest() {
@@ -242,9 +242,10 @@ SvgAffineTest::test_t const SvgAffineTest::write_scale_tests[3] = {
     {"scale(0)",Geom::Affine(0,0,0,0,0,0)},
     {"scale(7)",Geom::Affine(7,0,0,7,0,0)},
     {"scale(2,3)",Geom::Affine(2,0,0,3,0,0)}};
-SvgAffineTest::test_t const SvgAffineTest::write_rotate_tests[2] = {
+SvgAffineTest::test_t const SvgAffineTest::write_rotate_tests[3] = {
     {"rotate(13)",Geom::Affine(cos(13.*DEGREE),sin(13.*DEGREE),-sin(13.*DEGREE),cos(13.*DEGREE),0,0)},
-    {"rotate(-13,7,11)",Geom::Affine(cos(-13.*DEGREE),sin(-13.*DEGREE),-sin(-13.*DEGREE),cos(-13.*DEGREE),(1-cos(-13.*DEGREE))*7+sin(-13.*DEGREE)*11,(1-cos(-13.*DEGREE))*11-sin(-13.*DEGREE)*7)}};
+    {"rotate(-13,7,11)",Geom::Affine(cos(-13.*DEGREE),sin(-13.*DEGREE),-sin(-13.*DEGREE),cos(-13.*DEGREE),(1-cos(-13.*DEGREE))*7+sin(-13.*DEGREE)*11,(1-cos(-13.*DEGREE))*11-sin(-13.*DEGREE)*7)},
+    {"rotate(-34.5,6.7,89)",Geom::Affine(cos(-34.5*DEGREE),sin(-34.5*DEGREE),-sin(-34.5*DEGREE),cos(-34.5*DEGREE),(1-cos(-34.5*DEGREE))*6.7+sin(-34.5*DEGREE)*89,(1-cos(-34.5*DEGREE))*89-sin(-34.5*DEGREE)*6.7)}};
 SvgAffineTest::test_t const SvgAffineTest::write_skew_tests[3] = {
     {"skewX(30)",Geom::Affine(1,0,tan(30.*DEGREE),1,0,0)},
     {"skewX(-30)",Geom::Affine(1,0,tan(-30.*DEGREE),1,0,0)},
diff --git a/src/svg/svg-affine.cpp b/src/svg/svg-affine.cpp
index af58c4544..c853f9930 100644
--- a/src/svg/svg-affine.cpp
+++ b/src/svg/svg-affine.cpp
@@ -217,29 +217,29 @@ sp_svg_transform_write(Geom::Affine const &transform)
 
         c[p++] = ')';
         c[p] = '\000';
-    /* } else if (transform.withoutTranslation().isRotation()) {
-        // FIXME someone please figure out if this can actually be done
-        // The rotation angle is correct, the points are not
+    } else if (transform.withoutTranslation().isRotation()) {
+        // Solution found by Johan Engelen
         // Refer to the matrix in svg-affine-test.h
 
         // We are a rotation about a special axis
         strcpy(c + p, "rotate(");
         p += 7;
 
-        Geom::Affine const sans_translate = transform.withoutTranslation();
-        double angle = std::atan2(sans_translate[1], sans_translate[0]) * (180 / M_PI);
+        double angle = std::atan2(transform[1], transform[0]) * (180 / M_PI);
         p += sp_svg_number_write_de(c + p, sizeof(c) - p, angle, prec, min_exp);
         c[p++] = ',';
 
-        Geom::Point pt = transform.translation();
-        p += sp_svg_number_write_de(c + p, sizeof(c) - p, pt[Geom::X], prec, min_exp);
+        Geom::Affine const& m = transform;
+        double tx = (m[2]*m[5]+m[4]-m[4]*m[3]) / (1-m[3]-m[0]+m[0]*m[3]-m[2]*m[1]);
+        p += sp_svg_number_write_de(c + p, sizeof(c) - p, tx, prec, min_exp);
 
         c[p++] = ',';
 
-        p += sp_svg_number_write_de(c + p, sizeof(c) - p, pt[Geom::Y], prec, min_exp);
+        double ty = (m[1]*tx + m[5]) / (1 - m[3]);
+        p += sp_svg_number_write_de(c + p, sizeof(c) - p, ty, prec, min_exp);
 
         c[p++] = ')';
-        c[p] = '\000';*/
+        c[p] = '\000';
     } else if (transform.isHShear()) {
         // We are more or less a pure skewX
         strcpy(c + p, "skewX(");