From: Thomas Petazzoni <thomas.petazz...@free-electrons.com> Mapnik is current using context.set_matrix() to modify the Cairo transformation matrix to render markers at the right location and with the right angle on the map. This is typically used to render one-way arrows with the MapQuest stylesheet.
Unfortunately, context.set_matrix() completely _overrides_ the existing Cairo transformation matrix instead of making an _additional_ transformation to it. However, in MapOSMatic (http://www.maposmatic.org), for our map-rendering needs, we pass to Mapnik a Cairo surface on which we have already applied a translation+scaling transformation. The usage of .set_matrix() by Mapnik completely overrides this transformation, with the result of having completely misplaced one-way arrows. By using context.transform(), then the transformation matrix is applied on _top_ of the current one, which fixes the rendering. Now, the one-way arrows are at the right locations on our translated+scaled Cairo surface. Thanks to Gaël Utard <gael.ut...@kisis.fr> for his help in debugging this problem. Signed-off-by: Thomas Petazzoni <thomas.petazz...@free-electrons.com> --- src/cairo_renderer.cpp | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/src/cairo_renderer.cpp b/src/cairo_renderer.cpp index 589247e..12f6277 100644 --- a/src/cairo_renderer.cpp +++ b/src/cairo_renderer.cpp @@ -1269,7 +1269,7 @@ void cairo_renderer_base::start_map_processing(Map const& map) double x, y, angle; while (placement.get_point(&x, &y, &angle)) { Cairo::Matrix matrix = Cairo::rotation_matrix(angle) * Cairo::translation_matrix(x,y) ; - context.set_matrix(matrix); + context.transform(matrix); context.add_path(arrow_); } } -- 1.7.4.1
