path: root/src/vec_core.cpp

/*
 * This file is part of gerbolyze, a vector image preprocessing toolchain 
 * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 * 
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

#include <cmath>
#include <string>
#include <iostream>
#include <vector>
#include <opencv2/opencv.hpp>
#include "svg_import_util.h"
#include "vec_core.h"
#include "svg_import_defs.h"
#include "jc_voronoi.h"

using namespace gerbolyze;
using namespace std;

/* debug function */
static void dbg_show_cv_image(cv::Mat &img) {
    string windowName = "Debug image";
    cv::namedWindow(windowName);
    cv::imshow(windowName, img);
    cv::waitKey(0);
    cv::destroyWindow(windowName);
}

/* From jcv voronoi README */
static void voronoi_relax_points(const jcv_diagram* diagram, jcv_point* points) {
    const jcv_site* sites = jcv_diagram_get_sites(diagram);
    for (int i=0; i<diagram->numsites; i++) {
        const jcv_site* site = &sites[i];
        jcv_point sum = site->p;
        int count = 1;

        const jcv_graphedge* edge = site->edges;

        while (edge) {
            sum.x += edge->pos[0].x;
            sum.y += edge->pos[0].y;
            count++;
            edge = edge->next;
        }

        points[site->index].x = sum.x / count;
        points[site->index].y = sum.y / count;
    }
} 

/* Render image into gerber file.
 *
 * This function renders an image into a number of vector primitives emulating the images grayscale brightness by
 * differently sized vector shaped giving an effect similar to halftone printing used in newspapers.
 *
 * On a high level, this function does this in four steps:
 * 1. It preprocesses the source image at the pixel level. This involves several tasks:
 *    1.1. It converts the image to grayscale.
 *    1.2. It scales the image up or down to match the given minimum feature size.
 *    1.3. It applies a blur depending on the given minimum feature size to prevent aliasing artifacts.
 * 2. It randomly spread points across the image using poisson disc sampling. This yields points that have a fairly even
 *    average distance to each other across the image, and that have a guaranteed minimum distance that depends on
 *    minimum feature size.
 * 3. It calculates a voronoi map based on this set of points and it calculats the polygon shape of each cell of the
 *    voronoi map.
 * 4. It scales each of these voronoi cell polygons to match the input images brightness at the spot covered by this
 *    cell.
 */
void gerbolyze::vectorize_image(cairo_t *cr, const pugi::xml_node &node, double min_feature_size_px, ClipperLib::Paths &clip_path, cairo_matrix_t &viewport_matrix, PolygonSink &sink) {
    /* Read XML node attributes */
    auto x = usvg_double_attr(node, "x", 0.0);
    auto y = usvg_double_attr(node, "y", 0.0);
    auto width = usvg_double_attr(node, "width", 0.0);
    auto height = usvg_double_attr(node, "height", 0.0);
    assert (width > 0 && height > 0);
    cerr << "image elem: w="<<width<<", h="<<height<<endl;

    /* Read image from data:base64... URL */
    string img_data = parse_data_iri(node.attribute("xlink:href").value());
    if (img_data.empty()) {
        cerr << "Warning: Empty or invalid image element with id \"" << node.attribute("id").value() << "\"" << endl;
        return;
    }

    /* slightly annoying round-trip through the std:: and cv:: APIs */
    vector<unsigned char> img_vec(img_data.begin(), img_data.end());
    cv::Mat data_mat(img_vec, true);
    cv::Mat img = cv::imdecode(data_mat, cv::ImreadModes::IMREAD_GRAYSCALE | cv::ImreadModes::IMREAD_ANYDEPTH);
    data_mat.release();

    if (img.empty()) {
        cerr << "Warning: Could not decode content of image element with id \"" << node.attribute("id").value() << "\"" << endl;
        return;
    }

    /* Set up target transform using SVG transform and x/y attributes */
    cairo_save(cr);
    apply_cairo_transform_from_svg(cr, node.attribute("transform").value());
    cairo_translate(cr, x, y);

    /* Adjust minimum feature size given in mm and translate into px document units in our local coordinate system. */
    double f_x = min_feature_size_px, f_y = 0;
    cairo_device_to_user_distance(cr, &f_x, &f_y);
    min_feature_size_px = sqrt(f_x*f_x + f_y*f_y);

    /* For both our debug SVG output and for the gerber output, we have to paint the image's bounding box in black as
     * background for our halftone blobs. We cannot simply draw a rect here, though. Instead we have to first intersect
     * the bounding box with the clip path we get from the caller, then we have to translate it into Cairo-SVG's
     * document units. */
    /* First, setup the bounding box rectangle in our local px coordinate space. */
    ClipperLib::Path rect_path;
    for (auto &elem : vector<pair<double, double>> {{0, 0}, {width, 0}, {width, height}, {0, height}}) {
        double x = elem.first, y = elem.second;
        cairo_user_to_device(cr, &x, &y);
        rect_path.push_back({ (ClipperLib::cInt)round(x * clipper_scale), (ClipperLib::cInt)round(y * clipper_scale) });
    }

    /* Intersect the bounding box with the caller's clip path */
    ClipperLib::Clipper c;
    c.AddPath(rect_path, ClipperLib::ptSubject, /* closed */ true);
    if (!clip_path.empty()) {
        c.AddPaths(clip_path, ClipperLib::ptClip, /* closed */ true);
    }

    ClipperLib::Paths rect_out;
    c.StrictlySimple(true);
    c.Execute(ClipperLib::ctIntersection, rect_out, ClipperLib::pftNonZero, ClipperLib::pftNonZero);

    /* Finally, translate into Cairo-SVG's document units and draw. */
    cairo_save(cr);
    cairo_set_matrix(cr, &viewport_matrix);
    cairo_new_path(cr);
    ClipperLib::cairo::clipper_to_cairo(rect_out, cr, CAIRO_PRECISION, ClipperLib::cairo::tNone);
    cairo_set_source_rgba (cr, 0.0, 0.0, 0.0, 1.0);
    /* First, draw into SVG */
    cairo_fill(cr);
    cairo_restore(cr);

    /* Second, draw into gerber. */
    cairo_save(cr);
    cairo_identity_matrix(cr);
    for (const auto &poly : rect_out) {
        vector<array<double, 2>> out;
        for (const auto &p : poly)
            out.push_back(std::array<double, 2>{
                    ((double)p.X) / clipper_scale, ((double)p.Y) / clipper_scale
                    });
        sink << GRB_POL_CLEAR << out;
    }
    cairo_restore(cr);

    /* Set up a poisson-disc sampled point "grid" covering the image. Calculate poisson disc parameters from given
     * minimum feature size. */
    double grayscale_overhead = 0.8; /* fraction of distance between two adjacent cell centers that is reserved for
                                        grayscale interpolation. Larger values -> better grayscale resolution,
                                        larger cells. */
    double center_distance = min_feature_size_px * 2.0 * (1.0 / (1.0-grayscale_overhead));
    vector<d2p> *grid_centers = sample_poisson_disc(width, height, min_feature_size_px * 2.0 * 2.0);
    /* TODO make these alternative grids available to callers */
    //vector<d2p> *grid_centers = sample_hexgrid(width, height, center_distance);
    //vector<d2p> *grid_centers = sample_squaregrid(width, height, center_distance);

    /* Target factor between given min_feature_size and intermediate image pixels,
     * i.e. <scale_featuresize_factor> px ^= min_feature_size */
    double scale_featuresize_factor = 3.0;
    /* TODO: support for preserveAspectRatio attribute */
    double px_w = width / min_feature_size_px * scale_featuresize_factor;
    double px_h = height / min_feature_size_px * scale_featuresize_factor;

    /* Scale intermediate image (step 1.2) to have <scale_featuresize_factor> pixels per min_feature_size. */ 
    cv::Mat scaled(cv::Size{(int)round(px_w), (int)round(px_h)}, img.type());
    cv::resize(img, scaled, scaled.size(), 0, 0);
    img.release();

    /* Blur image with a kernel larger than our minimum feature size to avoid aliasing. */
    cv::Mat blurred(scaled.size(), scaled.type());
    int blur_size = (int)ceil(fmax(scaled.cols / width, scaled.rows / height) * center_distance);
    cv::GaussianBlur(scaled, blurred, {blur_size, blur_size}, 0, 0);
    scaled.release();
    
    /* Calculate voronoi diagram for the grid generated above. */
    jcv_diagram diagram;
    memset(&diagram, 0, sizeof(jcv_diagram));
    jcv_rect rect {{0.0, 0.0}, {width, height}};
    jcv_point *pts = reinterpret_cast<jcv_point *>(grid_centers->data()); /* hackety hack */
    jcv_diagram_generate(grid_centers->size(), pts, &rect, 0, &diagram);
    /* Relax points, i.e. wiggle them around a little bit to equalize differences between cell sizes a little bit. */
    voronoi_relax_points(&diagram, pts);
    memset(&diagram, 0, sizeof(jcv_diagram));
    jcv_diagram_generate(grid_centers->size(), pts, &rect, 0, &diagram);
    
    /* For each voronoi cell calculated above, find the brightness of the blurred image pixel below its center. We do
     * not have to average over the entire cell's area here: The blur is doing a good approximation of that while being
     * simpler and faster.
     *
     * We do this step before generating the cell poygons below because we have to look up a cell's neighbor's fill
     * factor during gap filling for minimum feature size preservation. */
    vector<double> fill_factors(diagram.numsites); /* Factor to be multiplied with site polygon radius to yield target
                                                      fill level */
    const jcv_site* sites = jcv_diagram_get_sites(&diagram);
    int j = 0;
    for (int i=0; i<diagram.numsites; i++) {
        const jcv_point center = sites[i].p;

        double pxd = (double)blurred.at<unsigned char>(
                (int)round(center.y / height * blurred.rows),
                (int)round(center.x / width * blurred.cols)) / 255.0; 
        fill_factors[sites[i].index] = sqrt(pxd);
    }

    /* Minimum gap between adjacent scaled site polygons. */
    double min_gap_px = min_feature_size_px;
    vector<double> adjusted_fill_factors;
    adjusted_fill_factors.reserve(32); /* Vector to hold adjusted fill factors for each edge for gap filling */
    /* now iterate over all voronoi cells again to generate each cell's scaled polygon halftone blob. */
    for (int i=0; i<diagram.numsites; i++) {
        const jcv_point center = sites[i].p;
        double fill_factor_ours = fill_factors[sites[i].index];
        
        /* Do not render halftone blobs that are too small */
        if (fill_factor_ours * 0.5 * center_distance < min_gap_px)
            continue;

        /* Iterate over this cell's edges. For each edge, check the gap that would result between this cell's halftone
         * blob and the neighboring cell's halftone blob based on their fill factors. If the gap is too small, either
         * widen it by adjusting both fill factors down a bit (for this edge only!), or eliminate it by setting both
         * fill factors to 1.0 (again, for this edge only!). */
        adjusted_fill_factors.clear();
        const jcv_graphedge* e = sites[i].edges;
        while (e) {
            /* half distance between both neighbors of this edge, i.e. sites[i] and its neighbor. */
            /* Note that in a voronoi tesselation, this edge is always halfway between. */
            double adjusted_fill_factor = fill_factor_ours;

            if (e->neighbor != nullptr) { /* nullptr -> edge is on the voronoi map's border */
                double rad = sqrt(pow(center.x - e->neighbor->p.x, 2) + pow(center.y - e->neighbor->p.y, 2)) / 2.0;
                double fill_factor_theirs = fill_factors[e->neighbor->index];
                double gap_px = (1.0 - fill_factor_ours) * rad + (1.0 - fill_factor_theirs) * rad;

                if (gap_px > min_gap_px) {
                    /* all good. gap is wider than minimum. */
                } else if (gap_px > 0.5 * min_gap_px) {
                    /* gap is narrower than minimum, but more than half of minimum width. */
                    /* force gap open, distribute adjustment evenly on left/right */
                    double fill_factor_adjustment = (min_gap_px - gap_px) / 2.0 / rad;
                    adjusted_fill_factor -= fill_factor_adjustment;
                } else {
                    /* gap is less than half of minimum width. Force gap closed. */
                    adjusted_fill_factor = 1.0;
                }
            }
            adjusted_fill_factors.push_back(adjusted_fill_factor);
            e = e->next;
        }

        /* Now, generate the actual halftone blob polygon */
        ClipperLib::Path cell_path;
        double last_fill_factor = adjusted_fill_factors.back();
        e = sites[i].edges;
        j = 0;
        while (e) {
            double fill_factor = adjusted_fill_factors[j];
            if (last_fill_factor != fill_factor) {
                /* Fill factor was adjusted since last edge, so generate one extra point so we have a nice radial
                 * "step". */
                double x = e->pos[0].x;
                double y = e->pos[0].y;
                x = center.x + (x - center.x) * fill_factor;
                y = center.y + (y - center.y) * fill_factor;

                cairo_user_to_device(cr, &x, &y);
                cell_path.push_back({ (ClipperLib::cInt)round(x * clipper_scale), (ClipperLib::cInt)round(y * clipper_scale) });
            }

            /* Emit endpoint of current edge */
            double x = e->pos[1].x;
            double y = e->pos[1].y;
            x = center.x + (x - center.x) * fill_factor;
            y = center.y + (y - center.y) * fill_factor;

            cairo_user_to_device(cr, &x, &y);
            cell_path.push_back({ (ClipperLib::cInt)round(x * clipper_scale), (ClipperLib::cInt)round(y * clipper_scale) });

            j += 1;
            last_fill_factor = fill_factor;
            e = e->next;
        }

        /* Now, clip the halftone blob generated above against the given clip path. We do this individually for each
         * blob since this way is *much* faster than throwing a million blobs at once at poor clipper. */
        ClipperLib::Paths polys;
        ClipperLib::Clipper c;
        c.AddPath(cell_path, ClipperLib::ptSubject, /* closed */ true);
        if (!clip_path.empty()) {
            c.AddPaths(clip_path, ClipperLib::ptClip, /* closed */ true);
        }
        c.StrictlySimple(true);
        c.Execute(ClipperLib::ctIntersection, polys, ClipperLib::pftNonZero, ClipperLib::pftNonZero);

        /* Export halftone blob to debug svg */
        cairo_save(cr);
        cairo_set_matrix(cr, &viewport_matrix);
        cairo_new_path(cr);
        ClipperLib::cairo::clipper_to_cairo(polys, cr, CAIRO_PRECISION, ClipperLib::cairo::tNone);
        cairo_set_source_rgba(cr, 1, 1, 1, 1);
        cairo_fill(cr);
        cairo_restore(cr);

        /* And finally, export halftone blob to gerber. */
        cairo_save(cr);
        cairo_identity_matrix(cr);
        for (const auto &poly : polys) {
            vector<array<double, 2>> out;
            for (const auto &p : poly)
                out.push_back(std::array<double, 2>{
                        ((double)p.X) / clipper_scale, ((double)p.Y) / clipper_scale
                        });
            sink << GRB_POL_DARK << out;
        }
        cairo_restore(cr);
    }

    blurred.release();
    jcv_diagram_free( &diagram );
    delete grid_centers;
    cairo_restore(cr);
}