path: root/src/display/control/canvas-axonomgrid.cpp

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Authors:
 *    Johan Engelen <j.b.c.engelen@alumnus.utwente.nl>
 *
 * Copyright (C) 2006-2012 Authors
 * Released under GNU GPL v2+, read the file 'COPYING' for more information.
 */

/*
 * Current limits are: one axis (y-axis) is always vertical. The other two
 * axes are bound to a certain range of angles. The z-axis always has an angle
 * smaller than 90 degrees (measured from horizontal, 0 degrees being a line extending
 * to the right). The x-axis will always have an angle between 0 and 90 degrees.
 */

#include <gtkmm/box.h>
#include <gtkmm/label.h>
#include <gtkmm/grid.h>

#include <glibmm/i18n.h>

#include <2geom/angle.h>
#include <2geom/line.h>

#include "canvas-axonomgrid.h"
#include "canvas-grid.h"
#include "canvas-item-grid.h"

#include "desktop.h"
#include "document.h"
#include "inkscape.h"
#include "preferences.h"

#include "display/cairo-utils.h"

#include "helper/mathfns.h"

#include "object/sp-namedview.h"
#include "object/sp-object.h"
#include "object/sp-root.h"

#include "svg/svg-color.h"

#include "ui/widget/canvas.h"
#include "ui/widget/registered-widget.h"

#include "util/units.h"

using Inkscape::Util::unit_table;

enum Dim3 { X=0, Y, Z };

/**
 * This function calls Cairo to render a line on a particular canvas buffer.
 * Coordinates are interpreted as SCREENcoordinates
 */
static void
sp_caxonomgrid_drawline (Inkscape::CanvasItemBuffer *buf, gint x0, gint y0, gint x1, gint y1, guint32 rgba)
{
    buf->cr->move_to(0.5 + x0, 0.5 + y0);
    buf->cr->line_to(0.5 + x1, 0.5 + y1);
    buf->cr->set_source_rgba(SP_RGBA32_R_F(rgba), SP_RGBA32_G_F(rgba),
                             SP_RGBA32_B_F(rgba), SP_RGBA32_A_F(rgba));
    buf->cr->stroke();
}

static void
sp_grid_vline (Inkscape::CanvasItemBuffer *buf, gint x, gint ys, gint ye, guint32 rgba)
{
    if ((x < buf->rect.left()) || (x >= buf->rect.right()))
        return;

    buf->cr->move_to(0.5 + x, 0.5 + ys);
    buf->cr->line_to(0.5 + x, 0.5 + ye);
    buf->cr->set_source_rgba(SP_RGBA32_R_F(rgba), SP_RGBA32_G_F(rgba),
                             SP_RGBA32_B_F(rgba), SP_RGBA32_A_F(rgba));
    buf->cr->stroke();
}

namespace Inkscape {


CanvasAxonomGrid::CanvasAxonomGrid (SPNamedView * nv, Inkscape::XML::Node * in_repr, SPDocument * in_doc)
    : CanvasGrid(nv, in_repr, in_doc, GRID_AXONOMETRIC)
{
    Inkscape::Preferences *prefs = Inkscape::Preferences::get();
    gridunit = unit_table.getUnit(prefs->getString("/options/grids/axonom/units"));
    if (!gridunit) {
        gridunit = unit_table.getUnit("px");
    }
    origin[Geom::X] = Inkscape::Util::Quantity::convert(prefs->getDouble("/options/grids/axonom/origin_x", 0.0), gridunit, "px");
    origin[Geom::Y] = Inkscape::Util::Quantity::convert(prefs->getDouble("/options/grids/axonom/origin_y", 0.0), gridunit, "px");
    color = prefs->getInt("/options/grids/axonom/color", GRID_DEFAULT_COLOR);
    empcolor = prefs->getInt("/options/grids/axonom/empcolor", GRID_DEFAULT_EMPCOLOR);
    empspacing = prefs->getInt("/options/grids/axonom/empspacing", 5);
    lengthy = Inkscape::Util::Quantity::convert(prefs->getDouble("/options/grids/axonom/spacing_y", 1.0), gridunit, "px");
    angle_deg[X] = prefs->getDouble("/options/grids/axonom/angle_x", 30.0);
    angle_deg[Z] = prefs->getDouble("/options/grids/axonom/angle_z", 30.0);
    angle_deg[Y] = 0;

    angle_rad[X] = Geom::rad_from_deg(angle_deg[X]);
    tan_angle[X] = tan(angle_rad[X]);
    angle_rad[Z] = Geom::rad_from_deg(angle_deg[Z]);
    tan_angle[Z] = tan(angle_rad[Z]);

    snapper = new CanvasAxonomGridSnapper(this, &namedview->snap_manager, 0);

    if (repr) readRepr();
}

CanvasAxonomGrid::~CanvasAxonomGrid ()
{
    if (snapper) delete snapper;
}

static gboolean sp_nv_read_opacity(gchar const *str, guint32 *color)
{
    if (!str) {
        return FALSE;
    }

    gchar *u;
    gdouble v = g_ascii_strtod(str, &u);
    if (!u) {
        return FALSE;
    }
    v = CLAMP(v, 0.0, 1.0);

    *color = (*color & 0xffffff00) | (guint32) floor(v * 255.9999);

    return TRUE;
}



void
CanvasAxonomGrid::readRepr()
{
    SPRoot *root = doc->getRoot();
    double scale_x = 1.0;
    double scale_y = 1.0;
    if( root->viewBox_set ) {
        scale_x = root->width.computed  / root->viewBox.width();
        scale_y = root->height.computed / root->viewBox.height();
        if (Geom::are_near(scale_x / scale_y, 1.0, Geom::EPSILON)) {
            // scaling is uniform, try to reduce numerical error
            scale_x = (scale_x + scale_y)/2.0;
            double scale_none = Inkscape::Util::Quantity::convert(1, doc->getDisplayUnit(), "px");
            if (Geom::are_near(scale_x / scale_none, 1.0, Geom::EPSILON))
                scale_x = scale_none; // objects are same size, reduce numerical error
            scale_y = scale_x;
        }
    }

    gchar const *value;

    if ( (value = repr->attribute("originx")) ) {

        Inkscape::Util::Quantity q = unit_table.parseQuantity(value);

        if( q.unit->type == UNIT_TYPE_LINEAR ) {
            // Legacy grid not in 'user units'
            origin[Geom::X] = q.value("px");
        } else {
            // Grid in 'user units'
            origin[Geom::X] = q.quantity * scale_x;
        }
    }

    if ( (value = repr->attribute("originy")) ) {

        Inkscape::Util::Quantity q = unit_table.parseQuantity(value);

        if( q.unit->type == UNIT_TYPE_LINEAR ) {
            // Legacy grid not in 'user units'
            origin[Geom::Y] = q.value("px");
        } else {
            // Grid in 'user units'
            origin[Geom::Y] = q.quantity * scale_y;
        }
    }

    if ( (value = repr->attribute("spacingy")) ) {

        Inkscape::Util::Quantity q = unit_table.parseQuantity(value);

        if( q.unit->type == UNIT_TYPE_LINEAR ) {
            // Legacy grid not in 'user units'
            lengthy = q.value("px");
        } else {
            // Grid in 'user units'
            lengthy = q.quantity * scale_y; // We do not handle scale_x != scale_y
        }
        if (lengthy < 0.0500) lengthy = 0.0500;
    }

    if ( (value = repr->attribute("gridanglex")) ) {
        angle_deg[X] = g_ascii_strtod(value, nullptr);
        if (angle_deg[X] < 0.) angle_deg[X] = 0.;
        if (angle_deg[X] > 89.0) angle_deg[X] = 89.0;
        angle_rad[X] = Geom::rad_from_deg(angle_deg[X]);
        tan_angle[X] = tan(angle_rad[X]);
    }

    if ( (value = repr->attribute("gridanglez")) ) {
        angle_deg[Z] = g_ascii_strtod(value, nullptr);
        if (angle_deg[Z] < 0.) angle_deg[Z] = 0.;
        if (angle_deg[Z] > 89.0) angle_deg[Z] = 89.0;
        angle_rad[Z] = Geom::rad_from_deg(angle_deg[Z]);
        tan_angle[Z] = tan(angle_rad[Z]);
    }

    if ( (value = repr->attribute("color")) ) {
        color = (color & 0xff) | sp_svg_read_color(value, color);
    }

    if ( (value = repr->attribute("empcolor")) ) {
        empcolor = (empcolor & 0xff) | sp_svg_read_color(value, empcolor);
    }

    if ( (value = repr->attribute("opacity")) ) {
        sp_nv_read_opacity(value, &color);
    }
    if ( (value = repr->attribute("empopacity")) ) {
        sp_nv_read_opacity(value, &empcolor);
    }

    if ( (value = repr->attribute("empspacing")) ) {
        empspacing = atoi(value);
    }

    if ( (value = repr->attribute("visible")) ) {
        visible = (strcmp(value,"false") != 0 && strcmp(value, "0") != 0);
    }

    if ( (value = repr->attribute("enabled")) ) {
        g_assert(snapper != nullptr);
        snapper->setEnabled(strcmp(value,"false") != 0 && strcmp(value, "0") != 0);
    }

    if ( (value = repr->attribute("snapvisiblegridlinesonly")) ) {
        g_assert(snapper != nullptr);
        snapper->setSnapVisibleOnly(strcmp(value,"false") != 0 && strcmp(value, "0") != 0);
    }

    if ( (value = repr->attribute("units")) ) {
        gridunit = unit_table.getUnit(value); // Display unit identifier in grid menu
    }

    for (auto grid : canvas_item_grids) {
        grid->request_update();
    }

    return;
}

/**
 * Called when XML node attribute changed; updates dialog widgets if change was not done by widgets themselves.
 */
void
CanvasAxonomGrid::onReprAttrChanged(Inkscape::XML::Node */*repr*/, gchar const */*key*/, gchar const */*oldval*/, gchar const */*newval*/, bool /*is_interactive*/)
{
    readRepr();

    if ( ! (_wr.isUpdating()) )
        updateWidgets();
}

Gtk::Widget *
CanvasAxonomGrid::newSpecificWidget()
{
    _rumg = Gtk::manage( new Inkscape::UI::Widget::RegisteredUnitMenu(
            _("Grid _units:"), "units", _wr, repr, doc) );
    _rsu_ox = Gtk::manage( new Inkscape::UI::Widget::RegisteredScalarUnit(
            _("_Origin X:"), _("X coordinate of grid origin"), "originx",
            *_rumg, _wr, repr, doc, Inkscape::UI::Widget::RSU_x) );
    _rsu_oy = Gtk::manage( new Inkscape::UI::Widget::RegisteredScalarUnit(
            _("O_rigin Y:"), _("Y coordinate of grid origin"), "originy",
            *_rumg, _wr, repr, doc, Inkscape::UI::Widget::RSU_y) );
    _rsu_sy = Gtk::manage( new Inkscape::UI::Widget::RegisteredScalarUnit(
            _("Spacing _Y:"), _("Base length of z-axis"), "spacingy",
            *_rumg, _wr, repr, doc, Inkscape::UI::Widget::RSU_y) );
    _rsu_ax = Gtk::manage( new Inkscape::UI::Widget::RegisteredScalar(
            _("Angle X:"), _("Angle of x-axis"), "gridanglex", _wr, repr, doc ) );
    _rsu_az = Gtk::manage(  new Inkscape::UI::Widget::RegisteredScalar(
            _("Angle Z:"), _("Angle of z-axis"), "gridanglez", _wr, repr, doc ) );

    _rcp_gcol = Gtk::manage( new Inkscape::UI::Widget::RegisteredColorPicker(
            _("Minor grid line _color:"), _("Minor grid line color"), _("Color of the minor grid lines"),
            "color", "opacity", _wr, repr, doc));
    _rcp_gmcol = Gtk::manage( new Inkscape::UI::Widget::RegisteredColorPicker(
            _("Ma_jor grid line color:"), _("Major grid line color"),
            _("Color of the major (highlighted) grid lines"),
            "empcolor", "empopacity", _wr, repr, doc));

    _rsi = Gtk::manage( new Inkscape::UI::Widget::RegisteredSuffixedInteger(
            _("_Major grid line every:"), "", _("lines"), "empspacing", _wr, repr, doc ) );

    _rumg->set_hexpand();
    _rsu_ox->set_hexpand();
    _rsu_oy->set_hexpand();
    _rsu_sy->set_hexpand();
    _rsu_ax->set_hexpand();
    _rsu_az->set_hexpand();
    _rcp_gcol->set_hexpand();
    _rcp_gmcol->set_hexpand();
    _rsi->set_hexpand();

    // set widget values
    _wr.setUpdating (true);

    _rsu_ox->setDigits(5);
    _rsu_ox->setIncrements(0.1, 1.0);

    _rsu_oy->setDigits(5);
    _rsu_oy->setIncrements(0.1, 1.0);

    _rsu_sy->setDigits(5);
    _rsu_sy->setIncrements(0.1, 1.0);

    _rumg->setUnit (gridunit->abbr);

    gdouble val;
    val = origin[Geom::X];
    val = Inkscape::Util::Quantity::convert(val, "px", gridunit);
    _rsu_ox->setValue (val);
    val = origin[Geom::Y];
    val = Inkscape::Util::Quantity::convert(val, "px", gridunit);
    _rsu_oy->setValue (val);
    val = lengthy;
    double gridy = Inkscape::Util::Quantity::convert(val, "px", gridunit);
    _rsu_sy->setValue (gridy);

    _rsu_ax->setValue(angle_deg[X]);
    _rsu_az->setValue(angle_deg[Z]);

    _rcp_gcol->setRgba32 (color);
    _rcp_gmcol->setRgba32 (empcolor);
    _rsi->setValue (empspacing);

    _wr.setUpdating (false);

    _rsu_ox->setProgrammatically = false;
    _rsu_oy->setProgrammatically = false;

    Gtk::Box *column = Gtk::manage(new Gtk::Box(Gtk::ORIENTATION_VERTICAL, 4));
    column->pack_start(*_rumg, true, false);
    column->pack_start(*_rsu_ox, true, false);
    column->pack_start(*_rsu_oy, true, false);
    column->pack_start(*_rsu_sy, true, false);
    column->pack_start(*_rsu_ax, true, false);
    column->pack_start(*_rsu_az, true, false);
    column->pack_start(*_rcp_gcol, true, false);
    column->pack_start(*_rcp_gmcol, true, false);
    column->pack_start(*_rsi, true, false);

    return column;
}


/**
 * Update dialog widgets from object's values.
 */
void
CanvasAxonomGrid::updateWidgets()
{
    if (_wr.isUpdating()) return;

    //no widgets (grid created with the document, not with the dialog)
    if (!_rcb_visible) return;

    _wr.setUpdating (true);

    _rcb_visible->setActive(visible);
    if (snapper != nullptr) {
        _rcb_enabled->setActive(snapper->getEnabled());
        _rcb_snap_visible_only->setActive(snapper->getSnapVisibleOnly());
    }

    _rumg->setUnit (gridunit->abbr);

    gdouble val;

    val = origin[Geom::X];
    val = Inkscape::Util::Quantity::convert(val, "px", gridunit);
    _rsu_ox->setValue (val);

    val = origin[Geom::Y];
    val = Inkscape::Util::Quantity::convert(val, "px", gridunit);
    _rsu_oy->setValue (val);

    val = lengthy;
    val = Inkscape::Util::Quantity::convert(val, "px", gridunit);
    _rsu_sy->setValue (val);

    _rsu_ax->setValue(angle_deg[X]);
    _rsu_az->setValue(angle_deg[Z]);

    _rsu_ox->setProgrammatically = false;
    _rsu_oy->setProgrammatically = false;
    _rsu_sy->setProgrammatically = false;
    _rsu_ax->setProgrammatically = false;
    _rsu_az->setProgrammatically = false;

    _rcp_gcol->setRgba32 (color);
    _rcp_gmcol->setRgba32 (empcolor);
    _rsi->setValue (empspacing);

    _wr.setUpdating (false);
}



void
CanvasAxonomGrid::Update (Geom::Affine const &affine, unsigned int /*flags*/)
{
    ow = origin * affine;
    sw = Geom::Point(fabs(affine[0]),fabs(affine[3]));
    sw *= lengthy;

    scaled = false;

    for(int dim = 0; dim < 2; dim++) {
        gint scaling_factor = empspacing;

        if (scaling_factor <= 1)
            scaling_factor = 5;

        int watchdog = 0;
        while (  (sw[dim] < 8.0) & (watchdog < 100) ) {
            scaled = true;
            sw[dim] *= scaling_factor;
            // First pass, go up to the major line spacing, then
            // keep increasing by two.
            scaling_factor = 2;
            watchdog++;
        }

    }

    spacing_ylines = sw[Geom::X] /(tan_angle[X] + tan_angle[Z]);
    lyw            = sw[Geom::Y];
    lxw_x          = Geom::are_near(tan_angle[X],0.) ? Geom::infinity() : sw[Geom::X] / tan_angle[X];
    lxw_z          = Geom::are_near(tan_angle[Z],0.) ? Geom::infinity() : sw[Geom::X] / tan_angle[Z];

    if (empspacing == 0) {
        scaled = true;
    }
}

void
CanvasAxonomGrid::Render (Inkscape::CanvasItemBuffer *buf)
{
    //set correct coloring, depending preference (when zoomed out, always major coloring or minor coloring)
    Inkscape::Preferences *prefs = Inkscape::Preferences::get();
    guint32 _empcolor;
    guint32 _color = color;
    bool preference = prefs->getBool("/options/grids/no_emphasize_when_zoomedout", false);
    if( scaled && preference ) {
        _empcolor = color;
    } else {
        _empcolor = empcolor;
    }

    bool xrayactive = prefs->getBool("/desktop/xrayactive", false);
    if (xrayactive) {  //this allow good looking on xray zones
        guint32 bg = 0xffffffff;
        _color = SP_RGBA32_F_COMPOSE(
                CLAMP(((1 - SP_RGBA32_A_F(_color)) * SP_RGBA32_R_F(bg)) + (SP_RGBA32_A_F(_color) * SP_RGBA32_R_F(_color)), 0.0, 1.0),
                CLAMP(((1 - SP_RGBA32_A_F(_color)) * SP_RGBA32_G_F(bg)) + (SP_RGBA32_A_F(_color) * SP_RGBA32_G_F(_color)), 0.0, 1.0),
                CLAMP(((1 - SP_RGBA32_A_F(_color)) * SP_RGBA32_B_F(bg)) + (SP_RGBA32_A_F(_color) * SP_RGBA32_B_F(_color)), 0.0, 1.0),
                1.0);
        _empcolor = SP_RGBA32_F_COMPOSE(
                CLAMP(((1 - SP_RGBA32_A_F(_empcolor)) * SP_RGBA32_R_F(bg)) + (SP_RGBA32_A_F(_empcolor) * SP_RGBA32_R_F(_empcolor)), 0.0, 1.0),
                CLAMP(((1 - SP_RGBA32_A_F(_empcolor)) * SP_RGBA32_G_F(bg)) + (SP_RGBA32_A_F(_empcolor) * SP_RGBA32_G_F(_empcolor)), 0.0, 1.0),
                CLAMP(((1 - SP_RGBA32_A_F(_empcolor)) * SP_RGBA32_B_F(bg)) + (SP_RGBA32_A_F(_empcolor) * SP_RGBA32_B_F(_empcolor)), 0.0, 1.0),
                1.0);
    }

    buf->cr->save();
    buf->cr->translate(-buf->rect.left(), -buf->rect.top());
    buf->cr->set_line_width(1.0);
    buf->cr->set_line_cap(Cairo::LINE_CAP_SQUARE);

    // gc = gridcoordinates (the coordinates calculated from the grids origin 'grid->ow'.
    // sc = screencoordinates ( for example "buf->rect.left()" is in screencoordinates )
    // bc = buffer patch coordinates (x=0 on left side of page, y=0 on bottom of page)

    // tl = topleft ; br = bottomright
    Geom::Point buf_tl_gc;
    Geom::Point buf_br_gc;
    buf_tl_gc[Geom::X] = buf->rect.left()   - ow[Geom::X];
    buf_tl_gc[Geom::Y] = buf->rect.top()    - ow[Geom::Y];
    buf_br_gc[Geom::X] = buf->rect.right()  - ow[Geom::X];
    buf_br_gc[Geom::Y] = buf->rect.bottom() - ow[Geom::Y];

    // render the three separate line groups representing the main-axes

    // x-axis always goes from topleft to bottomright. (0,0) - (1,1)
    gdouble const xintercept_y_bc = (buf_tl_gc[Geom::X] * tan_angle[X]) - buf_tl_gc[Geom::Y] ;
    gdouble const xstart_y_sc = ( xintercept_y_bc - floor(xintercept_y_bc/lyw)*lyw ) + buf->rect.top();
    gint const xlinestart = round( (xstart_y_sc - buf_tl_gc[Geom::X]*tan_angle[X] - ow[Geom::Y]) / lyw );
    gint xlinenum = xlinestart;

    // lines starting on left side.

    for (gdouble y = xstart_y_sc; y < buf->rect.bottom(); y += lyw, xlinenum++) {
        gint const x0 = buf->rect.left();
        gint const y0 = round(y);
        gint x1 = x0 + round( (buf->rect.bottom() - y) / tan_angle[X] );
        gint y1 = buf->rect.bottom();
        if ( Geom::are_near(tan_angle[X],0.) ) {
            x1 = buf->rect.right();
            y1 = y0;
        }

        if (!scaled && (xlinenum % empspacing) != 0) {
            sp_caxonomgrid_drawline (buf, x0, y0, x1, y1, _color);
        } else {
            sp_caxonomgrid_drawline (buf, x0, y0, x1, y1, _empcolor);
        }
    }
    // lines starting from top side
    if (!Geom::are_near(tan_angle[X],0.))
    {
        gdouble const xstart_x_sc = buf->rect.left() + (lxw_x - (xstart_y_sc - buf->rect.top()) / tan_angle[X]) ;
        xlinenum = xlinestart-1;
        for (gdouble x = xstart_x_sc; x < buf->rect.right(); x += lxw_x, xlinenum--) {
            gint const y0 = buf->rect.top();
            gint const y1 = buf->rect.bottom();
            gint const x0 = round(x);
            gint const x1 = x0 + round( (y1 - y0) / tan_angle[X] );

            if (!scaled && (xlinenum % empspacing) != 0) {
                sp_caxonomgrid_drawline (buf, x0, y0, x1, y1, _color);
            } else {
                sp_caxonomgrid_drawline (buf, x0, y0, x1, y1, _empcolor);
            }
        }
    }

    // y-axis lines (vertical)
    gdouble const ystart_x_sc = floor (buf_tl_gc[Geom::X] / spacing_ylines) * spacing_ylines + ow[Geom::X];
    gint const  ylinestart = round((ystart_x_sc - ow[Geom::X]) / spacing_ylines);
    gint ylinenum = ylinestart;
    for (gdouble x = ystart_x_sc; x < buf->rect.right(); x += spacing_ylines, ylinenum++) {
        gint const x0 = floor(x); // sp_grid_vline will add 0.5 again, so we'll pre-emptively use floor()
        // instead of round() to avoid biasing the vertical lines to the right by half a pixel; see
        // CanvasXYGrid::Render() for more details
        if (!scaled && (ylinenum % empspacing) != 0) {
            sp_grid_vline (buf, x0, buf->rect.top(), buf->rect.bottom() - 1, _color);
        } else {
            sp_grid_vline (buf, x0, buf->rect.top(), buf->rect.bottom() - 1, _empcolor);
        }
    }

    // z-axis always goes from bottomleft to topright. (0,1) - (1,0)
    gdouble const zintercept_y_bc = (buf_tl_gc[Geom::X] * -tan_angle[Z]) - buf_tl_gc[Geom::Y] ;
    gdouble const zstart_y_sc = ( zintercept_y_bc - floor(zintercept_y_bc/lyw)*lyw ) + buf->rect.top();
    gint const  zlinestart = round( (zstart_y_sc + buf_tl_gc[Geom::X]*tan_angle[Z] - ow[Geom::Y]) / lyw );
    gint zlinenum = zlinestart;
    // lines starting from left side
    gdouble next_y = zstart_y_sc;
    for (gdouble y = zstart_y_sc; y < buf->rect.bottom(); y += lyw, zlinenum++, next_y = y) {
        gint const x0 = buf->rect.left();
        gint const y0 = round(y);
        gint x1 = x0 + round( (y - buf->rect.top() ) / tan_angle[Z] );
        gint y1 = buf->rect.top();
        if ( Geom::are_near(tan_angle[Z],0.) ) {
            x1 = buf->rect.right();
            y1 = y0;
        }

        if (!scaled && (zlinenum % empspacing) != 0) {
            sp_caxonomgrid_drawline (buf, x0, y0, x1, y1, _color);
        } else {
            sp_caxonomgrid_drawline (buf, x0, y0, x1, y1, _empcolor);
        }
    }
    // draw lines from bottom-up
    if (!Geom::are_near(tan_angle[Z],0.))
    {
        gdouble const zstart_x_sc = buf->rect.left() + (next_y - buf->rect.bottom()) / tan_angle[Z] ;
        for (gdouble x = zstart_x_sc; x < buf->rect.right(); x += lxw_z, zlinenum++) {
            gint const y0 = buf->rect.bottom();
            gint const y1 = buf->rect.top();
            gint const x0 = round(x);
            gint const x1 = x0 + round(buf->rect.height() / tan_angle[Z] );

            if (!scaled && (zlinenum % empspacing) != 0) {
                sp_caxonomgrid_drawline (buf, x0, y0, x1, y1, _color);
            } else {
                sp_caxonomgrid_drawline (buf, x0, y0, x1, y1, _empcolor);
            }
        }
    }

    buf->cr->restore();
}

CanvasAxonomGridSnapper::CanvasAxonomGridSnapper(CanvasAxonomGrid *grid, SnapManager *sm, Geom::Coord const d) : LineSnapper(sm, d)
{
    this->grid = grid;
}

/**
 *  \return Snap tolerance (desktop coordinates); depends on current zoom so that it's always the same in screen pixels
 */
Geom::Coord CanvasAxonomGridSnapper::getSnapperTolerance() const
{
    SPDesktop const *dt = _snapmanager->getDesktop();
    double const zoom =  dt ? dt->current_zoom() : 1;
    return _snapmanager->snapprefs.getGridTolerance() / zoom;
}

bool CanvasAxonomGridSnapper::getSnapperAlwaysSnap() const
{
    return _snapmanager->snapprefs.getGridTolerance() == 10000; //TODO: Replace this threshold of 10000 by a constant; see also tolerance-slider.cpp
}

LineSnapper::LineList
CanvasAxonomGridSnapper::_getSnapLines(Geom::Point const &p) const
{
    LineList s;

    if ( grid == nullptr ) {
        return s;
    }

    SPDesktop const *dt = _snapmanager->getDesktop();
    double ta_x = grid->tan_angle[X];
    double ta_z = grid->tan_angle[Z];

    if (dt && dt->is_yaxisdown()) {
        std::swap(ta_x, ta_z);
    }

    double spacing_h;
    double spacing_v;

    if (getSnapVisibleOnly()) {
        // Only snapping to visible grid lines
        spacing_h = grid->spacing_ylines; // this is the spacing of the visible grid lines measured in screen pixels
        spacing_v = grid->lyw; // vertical
        // convert screen pixels to px
        // FIXME: after we switch to snapping dist in screen pixels, this will be unnecessary
        if (dt) {
            spacing_h /= dt->current_zoom();
            spacing_v /= dt->current_zoom();
        }
    } else {
        // Snapping to any grid line, whether it's visible or not
        spacing_h = grid->lengthy  /(grid->tan_angle[X] + grid->tan_angle[Z]);
        spacing_v = grid->lengthy;

    }

    // In an axonometric grid, any point will be surrounded by 6 grid lines:
    // - 2 vertical grid lines, one left and one right from the point
    // - 2 angled z grid lines, one above and one below the point
    // - 2 angled x grid lines, one above and one below the point

    // Calculate the x coordinate of the vertical grid lines
    Geom::Coord x_max = Inkscape::Util::round_to_upper_multiple_plus(p[Geom::X], spacing_h, grid->origin[Geom::X]);
    Geom::Coord x_min = Inkscape::Util::round_to_lower_multiple_plus(p[Geom::X], spacing_h, grid->origin[Geom::X]);

    // Calculate the y coordinate of the intersection of the angled grid lines with the y-axis
    double y_proj_along_z = p[Geom::Y] - ta_z * (p[Geom::X] - grid->origin[Geom::X]);
    double y_proj_along_x = p[Geom::Y] + ta_x * (p[Geom::X] - grid->origin[Geom::X]);
    double y_proj_along_z_max = Inkscape::Util::round_to_upper_multiple_plus(y_proj_along_z, spacing_v, grid->origin[Geom::Y]);
    double y_proj_along_z_min = Inkscape::Util::round_to_lower_multiple_plus(y_proj_along_z, spacing_v, grid->origin[Geom::Y]);
    double y_proj_along_x_max = Inkscape::Util::round_to_upper_multiple_plus(y_proj_along_x, spacing_v, grid->origin[Geom::Y]);
    double y_proj_along_x_min = Inkscape::Util::round_to_lower_multiple_plus(y_proj_along_x, spacing_v, grid->origin[Geom::Y]);

    // Calculate the versor for the angled grid lines
    Geom::Point vers_x = Geom::Point(1, -ta_x);
    Geom::Point vers_z = Geom::Point(1, ta_z);

    // Calculate the normal for the angled grid lines
    Geom::Point norm_x = Geom::rot90(vers_x);
    Geom::Point norm_z = Geom::rot90(vers_z);

    // The four angled grid lines form a parallelogram, enclosing the point
    // One of the two vertical grid lines divides this parallelogram in two triangles
    // We will now try to find out in which half (i.e. triangle) our point is, and return
    // only the three grid lines defining that triangle

    // The vertical grid line is at the intersection of two angled grid lines.
    // Now go find that intersection!
    Geom::Point p_x(0, y_proj_along_x_max);
    Geom::Line line_x(p_x, p_x + vers_x);
    Geom::Point p_z(0, y_proj_along_z_max);
    Geom::Line line_z(p_z, p_z + vers_z);

    Geom::OptCrossing inters = Geom::OptCrossing(); // empty by default
    try
    {
        inters = Geom::intersection(line_x, line_z);
    }
    catch (Geom::InfiniteSolutions &e)
    {
        // We're probably dealing with parallel lines; this is useless!
        return s;
    }

    // Determine which half of the parallelogram to use
    bool use_left_half = true;
    bool use_right_half = true;

    if (inters) {
        Geom::Point inters_pt = line_x.pointAt((*inters).ta);
        use_left_half = (p[Geom::X] - grid->origin[Geom::X]) < inters_pt[Geom::X];
        use_right_half = !use_left_half;
    }

    // Return the three grid lines which define the triangle that encloses our point
    // If we didn't find an intersection above, all 6 grid lines will be returned
    if (use_left_half) {
        s.push_back(std::make_pair(norm_z, Geom::Point(grid->origin[Geom::X], y_proj_along_z_max)));
        s.push_back(std::make_pair(norm_x, Geom::Point(grid->origin[Geom::X], y_proj_along_x_min)));
        s.push_back(std::make_pair(Geom::Point(1, 0), Geom::Point(x_max, 0)));
    }

    if (use_right_half) {
        s.push_back(std::make_pair(norm_z, Geom::Point(grid->origin[Geom::X], y_proj_along_z_min)));
        s.push_back(std::make_pair(norm_x, Geom::Point(grid->origin[Geom::X], y_proj_along_x_max)));
        s.push_back(std::make_pair(Geom::Point(1, 0), Geom::Point(x_min, 0)));
    }

    return s;
}

void CanvasAxonomGridSnapper::_addSnappedLine(IntermSnapResults &isr, Geom::Point const &snapped_point, Geom::Coord const &snapped_distance, SnapSourceType const &source, long source_num, Geom::Point const &normal_to_line, Geom::Point const &point_on_line) const
{
    SnappedLine dummy = SnappedLine(snapped_point, snapped_distance, source, source_num, Inkscape::SNAPTARGET_GRID, getSnapperTolerance(), getSnapperAlwaysSnap(), normal_to_line, point_on_line);
    isr.grid_lines.push_back(dummy);
}

void CanvasAxonomGridSnapper::_addSnappedPoint(IntermSnapResults &isr, Geom::Point const &snapped_point, Geom::Coord const &snapped_distance, SnapSourceType const &source, long source_num, bool constrained_snap) const
{
    SnappedPoint dummy = SnappedPoint(snapped_point, source, source_num, Inkscape::SNAPTARGET_GRID, snapped_distance, getSnapperTolerance(), getSnapperAlwaysSnap(), constrained_snap, true);
    isr.points.push_back(dummy);
}

void CanvasAxonomGridSnapper::_addSnappedLinePerpendicularly(IntermSnapResults &isr, Geom::Point const &snapped_point, Geom::Coord const &snapped_distance, SnapSourceType const &source, long source_num, bool constrained_snap) const
{
    SnappedPoint dummy = SnappedPoint(snapped_point, source, source_num, Inkscape::SNAPTARGET_GRID_PERPENDICULAR, snapped_distance, getSnapperTolerance(), getSnapperAlwaysSnap(), constrained_snap, true);
    isr.points.push_back(dummy);
}

bool CanvasAxonomGridSnapper::ThisSnapperMightSnap() const
{
    return _snap_enabled && _snapmanager->snapprefs.isTargetSnappable(Inkscape::SNAPTARGET_GRID);
}


}; // namespace Inkscape


/*
  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:fileencoding=utf-8:textwidth=99 :