src/display/inkscape-cairo.cpp

	inkscape-cairo.cpp revision 77eda576f455eeb23c7b92510f38bc60738473ab
/*
 * Helper functions to use cairo with inkscape
 *
 * Copyright (C) 2007 bulia byak
 * Copyright (C) 2008 Johan Engelen
 *
 * Released under GNU GPL
 *
 */

#include <cairo.h>

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#include <libnr/nr-pixblock.h>
#include <libnr/nr-convert2geom.h>
#include "../style.h"
#include "nr-arena.h"
#include "sp-canvas.h"
#include <2geom/pathvector.h>
#include <2geom/bezier-curve.h>
#include <2geom/hvlinesegment.h>
#include <2geom/matrix.h>
#include <2geom/point.h>
#include <2geom/path.h>
#include <2geom/transforms.h>
#include <2geom/sbasis-to-bezier.h>
#include "helper/geom-curves.h"

/** Creates a cairo context to render to the given pixblock on the given area */
cairo_t *
nr_create_cairo_context_for_data (NRRectL *area, NRRectL *buf_area, unsigned char *px, unsigned int rowstride)
{
    if (!nr_rect_l_test_intersect_ptr(buf_area, area))
        return NULL;

    NRRectL clip;
    nr_rect_l_intersect (&clip, buf_area, area);
    unsigned char *dpx = px + (clip.y0 - buf_area->y0) * rowstride + 4 * (clip.x0 - buf_area->x0);
    int width = area->x1 - area->x0;
    int height = area->y1 - area->y0;
    // even though cairo cannot draw in nonpremul mode, select ARGB32 for R8G8B8A8N as the closest; later eliminate R8G8B8A8N everywhere
    cairo_surface_t* cst = cairo_image_surface_create_for_data
        (dpx,
         CAIRO_FORMAT_ARGB32,
         width,
         height,
         rowstride);
    cairo_t *ct = cairo_create (cst);

    return ct;
}

/** Creates a cairo context to render to the given SPCanvasBuf on the given area */
cairo_t *
nr_create_cairo_context_canvasbuf (NRRectL */*area*/, SPCanvasBuf *b)
{
    return nr_create_cairo_context_for_data (&(b->rect), &(b->rect), b->buf, b->buf_rowstride);
}


/** Creates a cairo context to render to the given NRPixBlock on the given area */
cairo_t *
nr_create_cairo_context (NRRectL *area, NRPixBlock *pb)
{
    return nr_create_cairo_context_for_data (area, &(pb->area), NR_PIXBLOCK_PX (pb), pb->rs);
}

/*
 * Can be called recursively.
 * If optimize_stroke == false, the view Rect is not used.
 */
static void
feed_curve_to_cairo(cairo_t *cr, Geom::Curve const &c, Geom::Matrix const & trans, Geom::Rect view, bool optimize_stroke)
{
    if( is_straight_curve(c) )
    {
        Geom::Point end_tr = c.finalPoint() * trans;
        if (!optimize_stroke) {
            cairo_line_to(cr, end_tr[0], end_tr[1]);
        } else {
            Geom::Rect swept(c.initialPoint()*trans, end_tr);
            if (swept.intersects(view)) {
                cairo_line_to(cr, end_tr[0], end_tr[1]);
            } else {
                cairo_move_to(cr, end_tr[0], end_tr[1]);
            }
        }
    }
    else if(Geom::QuadraticBezier const *quadratic_bezier = dynamic_cast<Geom::QuadraticBezier const*>(&c)) {
        std::vector<Geom::Point> points = quadratic_bezier->points();
        points[0] *= trans;
        points[1] *= trans;
        points[2] *= trans;
        Geom::Point b1 = points[0] + (2./3) * (points[1] - points[0]);
        Geom::Point b2 = b1 + (1./3) * (points[2] - points[0]);
        if (!optimize_stroke) {
            cairo_curve_to(cr, b1[0], b1[1], b2[0], b2[1], points[2][0], points[2][1]);
        } else {
            Geom::Rect swept(points[0], points[2]);
            swept.expandTo(points[1]);
            if (swept.intersects(view)) {
                cairo_curve_to(cr, b1[0], b1[1], b2[0], b2[1], points[2][0], points[2][1]);
            } else {
                cairo_move_to(cr, points[2][0], points[2][1]);
            }
        }
    }
    else if(Geom::CubicBezier const *cubic_bezier = dynamic_cast<Geom::CubicBezier const*>(&c)) {
        std::vector<Geom::Point> points = cubic_bezier->points();
        //points[0] *= trans; // don't do this one here for fun: it is only needed for optimized strokes
        points[1] *= trans;
        points[2] *= trans;
        points[3] *= trans;
        if (!optimize_stroke) {
            cairo_curve_to(cr, points[1][0], points[1][1], points[2][0], points[2][1], points[3][0], points[3][1]);
        } else {
            points[0] *= trans;  // didn't transform this point yet
            Geom::Rect swept(points[0], points[3]);
            swept.expandTo(points[1]);
            swept.expandTo(points[2]);
            if (swept.intersects(view)) {
                cairo_curve_to(cr, points[1][0], points[1][1], points[2][0], points[2][1], points[3][0], points[3][1]);
            } else {
                cairo_move_to(cr, points[3][0], points[3][1]);
            }
        }
    }
//    else if(Geom::SVGEllipticalArc const *svg_elliptical_arc = dynamic_cast<Geom::SVGEllipticalArc *>(c)) {
//        //TODO: get at the innards and spit them out to cairo
//    }
    else {
        //this case handles sbasis as well as all other curve types
        Geom::Path sbasis_path = Geom::cubicbezierpath_from_sbasis(c.toSBasis(), 0.1);

        //recurse to convert the new path resulting from the sbasis to svgd
        for(Geom::Path::iterator iter = sbasis_path.begin(); iter != sbasis_path.end(); ++iter) {
            feed_curve_to_cairo(cr, *iter, trans, view, optimize_stroke);
        }
    }
}


/** Feeds path-creating calls to the cairo context translating them from the Path */
static void
feed_path_to_cairo (cairo_t *ct, Geom::Path const &path)
{
    if (path.empty())
        return;

    cairo_move_to(ct, path.initialPoint()[0], path.initialPoint()[1] );

    for(Geom::Path::const_iterator cit = path.begin(); cit != path.end_open(); ++cit) {
        feed_curve_to_cairo(ct, *cit, Geom::identity(), Geom::Rect(), false); // optimize_stroke is false, so the view rect is not used
    }

    if (path.closed()) {
        cairo_line_to(ct, path.initialPoint()[0], path.initialPoint()[1]);
//        cairo_close_path(ct);
        /* I think we should use cairo_close_path(ct) here but it doesn't work. (the closing line is not rendered completely)
           According to cairo documentation:
           The behavior of cairo_close_path() is distinct from simply calling cairo_line_to() with the equivalent coordinate
           in the case of stroking. When a closed sub-path is stroked, there are no caps on the ends of the sub-path. Instead,
           there is a line join connecting the final and initial segments of the sub-path.
        */
    }
}

/** Feeds path-creating calls to the cairo context translating them from the Path, with the given transform and shift */
static void
feed_path_to_cairo (cairo_t *ct, Geom::Path const &path, Geom::Matrix trans, NR::Maybe<NR::Rect> area, bool optimize_stroke, double stroke_width)
{
    if (!area || area->isEmpty())
        return;
    if (path.empty())
        return;

    // Transform all coordinates to coords within "area"
    Geom::Point shift = to_2geom(area->min());
    NR::Rect view = *area;
    view.growBy (stroke_width);
    view = view * from_2geom(Geom::Translate(-shift));
    //  Pass transformation to feed_curve, so that we don't need to create a whole new path.
    Geom::Matrix transshift(trans * Geom::Translate(-shift));

    Geom::Point initial = path.initialPoint() * transshift;
    cairo_move_to(ct, initial[0], initial[1] );

    for(Geom::Path::const_iterator cit = path.begin(); cit != path.end_open(); ++cit) {
        feed_curve_to_cairo(ct, *cit, transshift, to_2geom(view), optimize_stroke);
    }

    if (path.closed()) {
        cairo_line_to(ct, initial[0], initial[1]);
        /* It seems we cannot use cairo_close_path(ct) here; maybe because some parts of the path have been clipped and not drawn (maybe the before last segment was outside view area)
           However, according to cairo documentation:
           The behavior of cairo_close_path() is distinct from simply calling cairo_line_to() with the equivalent coordinate
           in the case of stroking. When a closed sub-path is stroked, there are no caps on the ends of the sub-path. Instead,
           there is a line join connecting the final and initial segments of the sub-path.
        */
    }
}

/** Feeds path-creating calls to the cairo context translating them from the PathVector, with the given transform and shift
 *  One must have done cairo_new_path(ct); before calling this function. */
void
feed_pathvector_to_cairo (cairo_t *ct, Geom::PathVector const &pathv, Geom::Matrix trans, NR::Maybe<NR::Rect> area, bool optimize_stroke, double stroke_width)
{
    if (!area || area->isEmpty())
        return;
    if (pathv.empty())
        return;

    for(Geom::PathVector::const_iterator it = pathv.begin(); it != pathv.end(); ++it) {
        feed_path_to_cairo(ct, *it, trans, area, optimize_stroke, stroke_width);
    }
}

/** Feeds path-creating calls to the cairo context translating them from the PathVector
 *  One must have done cairo_new_path(ct); before calling this function. */
void
feed_pathvector_to_cairo (cairo_t *ct, Geom::PathVector const &pathv)
{
    if (pathv.empty())
        return;

    for(Geom::PathVector::const_iterator it = pathv.begin(); it != pathv.end(); ++it) {
        feed_path_to_cairo(ct, *it);
    }
}

/*
  Local Variables:
  mode:c++
  c-file-style:"stroustrup"
  c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +))
  indent-tabs-mode:nil
  fill-column:99
  End:
*/
// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:encoding=utf-8:textwidth=99 :