diff options
Diffstat (limited to 'src/display/canvas-grid.cpp')
| -rw-r--r-- | src/display/canvas-grid.cpp | 17 |
1 files changed, 11 insertions, 6 deletions
diff --git a/src/display/canvas-grid.cpp b/src/display/canvas-grid.cpp index f4a210fe6..60d51de2e 100644 --- a/src/display/canvas-grid.cpp +++ b/src/display/canvas-grid.cpp @@ -911,6 +911,10 @@ CanvasXYGrid::Render (SPCanvasBuf *buf) cairo_set_line_width(buf->ct, 1.0); cairo_set_line_cap(buf->ct, CAIRO_LINE_CAP_SQUARE); + // Adding a 2 px margin to the buffer rectangle to avoid missing intersections (in case of rounding errors, and due to adding 0.5 below) + Geom::IntRect buf_rect_with_margin = buf->rect; + buf_rect_with_margin.expandBy(2); + for (unsigned dim = 0; dim < 2; ++dim) { // std::cout << "\n " << (dim==0?"Horizontal":"Vertical") << " ------------" << std::endl; @@ -932,7 +936,7 @@ CanvasXYGrid::Render (SPCanvasBuf *buf) for (unsigned c = 0; c < 4; ++c) { // We need signed distance... lib2geom offers only positive distance. - double distance = signed_distance( buf->rect.corner(c), axis ); + double distance = signed_distance( buf_rect_with_margin.corner(c), axis ); // Correct it for coordinate flips (inverts handedness). if (Geom::cross( axis.vector(), orth.vector() ) > 0 ) { @@ -956,7 +960,7 @@ CanvasXYGrid::Render (SPCanvasBuf *buf) Geom::Line grid_line = Geom::make_parallel_line( ow + j * sw[(dim+1)%2], axis ); - std::vector<Geom::Point> x = intersect_line_rectangle( grid_line, buf->rect ); + std::vector<Geom::Point> x = intersect_line_rectangle( grid_line, buf_rect_with_margin ); // If we have two intersections, grid line intersects buffer rectangle. if (x.size() == 2 ) { @@ -967,10 +971,11 @@ CanvasXYGrid::Render (SPCanvasBuf *buf) std::swap(x[0], x[1]); } - // Set up line. - cairo_move_to(buf->ct, x[0][Geom::X] + 0.5, x[0][Geom::Y] + 0.5); - cairo_line_to(buf->ct, x[1][Geom::X] + 0.5, x[1][Geom::Y] + 0.5); - + // Set up line. Need to use floor()+0.5 such that Cairo will draw us lines with a width of a single pixel, without any aliasing. + // For this we need to position the lines at exactly half pixels, see https://www.cairographics.org/FAQ/#sharp_lines + cairo_move_to(buf->ct, floor(x[0][Geom::X]) + 0.5, floor(x[0][Geom::Y]) + 0.5); + cairo_line_to(buf->ct, floor(x[1][Geom::X]) + 0.5, floor(x[1][Geom::Y]) + 0.5); + // Set dash pattern and color. if (render_dotted) { // alpha needs to be larger than in the line case to maintain a similar |