diff options
Diffstat (limited to 'src/sp-item-transform.cpp')
| -rw-r--r-- | src/sp-item-transform.cpp | 40 |
1 files changed, 29 insertions, 11 deletions
diff --git a/src/sp-item-transform.cpp b/src/sp-item-transform.cpp index 10eba6848..2ad7758a4 100644 --- a/src/sp-item-transform.cpp +++ b/src/sp-item-transform.cpp @@ -114,25 +114,43 @@ get_scale_transform_with_stroke (NR::Rect &bbox_param, gdouble strokewidth, bool return (p2o * direct * o2n); // can't solve the equation: one of the dimensions is equal to stroke width, so return the straightforward scaler } - gdouble ratio_x = (w1 - r0) / (w0 - r0); - gdouble ratio_y = (h1 - r0) / (h0 - r0); - NR::Matrix direct_constant_r = NR::Matrix (NR::scale(ratio_x, ratio_y)); + // Flip when the width or height changes sign + int flip_x = ((w1 < 0) == (w0 < 0)) ? 1 : -1; + int flip_y = ((h1 < 0) == (h0 < 0)) ? 1 : -1; + + // w1 and h1 can be negative, but if so then e.g. w1-r0 won't make sense + // therefore we should use fabs() all over the place + gdouble ratio_x = (fabs(w1) - fabs(r0)) / (fabs(w0) - fabs(r0)); + gdouble ratio_y = (fabs(h1) - fabs(r0)) / (fabs(h0) - fabs(r0)); + + NR::Matrix direct_constant_r = NR::Matrix (NR::scale(flip_x * ratio_x, flip_y*ratio_y)); if (transform_stroke && r0 != 0 && r0 != NR_HUGE) { // there's stroke, and we need to scale it // These coefficients are obtained from the assumption that scaling applies to the // non-stroked "shape proper" and that stroke scale is scaled by the expansion of that // matrix - gdouble A = -(w0 *h0) + r0*(w0 + h0); - gdouble B = -(w1 + h1) * r0*r0; - gdouble C = w1 * h1 * r0*r0; + // In fact, we're trying to solve this equation: + // r1 = r0 * sqrt (((w1-r0)/(w0-r0))*((h1-r1)/(h0-r0))) + // To make sense of this, the operant of the sqrt() should + // be positive, hence all the fabs() below + // (w1 and h1 will be negative when mirroring, w0 and h0 will probably never be negative) + gdouble A = -fabs(w0*h0) + fabs(r0)*(fabs(w0) + fabs(h0)); + gdouble B = -(fabs(w1) + fabs(h1)) * r0*r0; + gdouble C = fabs(w1 * h1 * r0*r0); if (B*B - 4*A*C > 0) { gdouble r1 = (-B - sqrt (B*B - 4*A*C))/(2*A); //gdouble r2 = (-B + sqrt (B*B - 4*A*C))/(2*A); //std::cout << "r0" << r0 << " r1" << r1 << " r2" << r2 << "\n"; - gdouble scale_x = (w1 - r1)/(w0 - r0); - gdouble scale_y = (h1 - r1)/(h0 - r0); - scale *= NR::scale(scale_x, scale_y); - unbudge *= NR::translate (-0.5 * (r0 * scale_x - r1), -0.5 * (r0 * scale_y - r1)); + // + // I think r1 will always be positive if r0 is (mathematical proof?) + // but if w1 becomes negative, then the scale will be wrong if we just do + // gdouble scale_x = (w1 - r1)/(w0 - r0); + // gdouble scale_y = (h1 - r1)/(h0 - r0); + // So let's do it like this: Calculate the absolute scale + gdouble scale_x = (fabs(w1) - fabs(r1))/(fabs(w0) - fabs(r0)); + gdouble scale_y = (fabs(h1) - fabs(r1))/(fabs(h0) - fabs(r0)); + scale *= NR::scale(flip_x*scale_x, flip_y*scale_y); + unbudge *= NR::translate (-flip_x * 0.5 * (fabs(r0) * scale_x - fabs(r1)), -flip_y * 0.5 * (fabs(r0) * scale_y - fabs(r1))); } else { scale *= direct; } @@ -141,7 +159,7 @@ get_scale_transform_with_stroke (NR::Rect &bbox_param, gdouble strokewidth, bool scale *= direct; } else {// nonscaling strokewidth scale *= direct_constant_r; - unbudge *= NR::translate (0.5 * r0 * (1 - ratio_x), 0.5 * r0 * (1 - ratio_y)); + unbudge *= NR::translate (flip_x * 0.5 * fabs(r0) * (1 - ratio_x), flip_y * 0.5 * fabs(r0) * (1 - ratio_y)); } } |