msdfgen/core/estimate-sdf-error.cpp

#include "estimate-sdf-error.h"

#include <cmath>
#include "arithmetics.hpp"

namespace msdfgen {

void scanlineSDF(Scanline &line, const BitmapConstRef<float, 1> &sdf, const Vector2 &scale, const Vector2 &translate, bool inverseYAxis, double y) {
    if (!(sdf.width > 0 && sdf.height > 0))
        return line.setIntersections(std::vector<Scanline::Intersection>());
    double pixelY = clamp(scale.x*(y+translate.y)-.5, double(sdf.height-1));
    if (inverseYAxis)
        pixelY = sdf.height-1-pixelY;
    int b = (int) floor(pixelY);
    int t = b+1;
    double bt = pixelY-b;
    if (t >= sdf.height) {
        b = sdf.height-1;
        t = sdf.height-1;
        bt = 1;
    }
    bool inside = false;
    std::vector<Scanline::Intersection> intersections;
    float lv, rv = mix(*sdf(0, b), *sdf(0, t), bt);
    if ((inside = rv > .5f)) {
        Scanline::Intersection intersection = { -1e240, 1 };
        intersections.push_back(intersection);
    }
    for (int l = 0, r = 1; r < sdf.width; ++l, ++r) {
        lv = rv;
        rv = mix(*sdf(r, b), *sdf(r, t), bt);
        if (lv != rv) {
            double lr = double(.5f-lv)/double(rv-lv);
            if (lr >= 0 && lr <= 1) {
                Scanline::Intersection intersection = { (l+lr+.5)/scale.x-translate.x, sign(rv-lv) };
                intersections.push_back(intersection);
            }
        }
    }
#ifdef MSDFGEN_USE_CPP11
    line.setIntersections((std::vector<Scanline::Intersection> &&) intersections);
#else
    line.setIntersections(intersections);
#endif
}

void scanlineSDF(Scanline &line, const BitmapConstRef<float, 3> &sdf, const Vector2 &scale, const Vector2 &translate, bool inverseYAxis, double y) {
    if (!(sdf.width > 0 && sdf.height > 0))
        return line.setIntersections(std::vector<Scanline::Intersection>());
    double pixelY = clamp(scale.x*(y+translate.y)-.5, double(sdf.height-1));
    if (inverseYAxis)
        pixelY = sdf.height-1-pixelY;
    int b = (int) floor(pixelY);
    int t = b+1;
    double bt = pixelY-b;
    if (t >= sdf.height) {
        b = sdf.height-1;
        t = sdf.height-1;
        bt = 1;
    }
    bool inside = false;
    std::vector<Scanline::Intersection> intersections;
    float lv[3], rv[3];
    rv[0] = mix(sdf(0, b)[0], sdf(0, t)[0], bt);
    rv[1] = mix(sdf(0, b)[1], sdf(0, t)[1], bt);
    rv[2] = mix(sdf(0, b)[2], sdf(0, t)[2], bt);
    if ((inside = median(rv[0], rv[1], rv[2]) > .5f)) {
        Scanline::Intersection intersection = { -1e240, 1 };
        intersections.push_back(intersection);
    }
    for (int l = 0, r = 1; r < sdf.width; ++l, ++r) {
        lv[0] = rv[0], lv[1] = rv[1], lv[2] = rv[2];
        rv[0] = mix(sdf(r, b)[0], sdf(r, t)[0], bt);
        rv[1] = mix(sdf(r, b)[1], sdf(r, t)[1], bt);
        rv[2] = mix(sdf(r, b)[2], sdf(r, t)[2], bt);
        Scanline::Intersection newIntersections[4];
        int newIntersectionCount = 0;
        for (int i = 0; i < 3; ++i) {
            if (lv[i] != rv[i]) {
                double lr = double(.5f-lv[i])/double(rv[i]-lv[i]);
                if (lr >= 0 && lr <= 1) {
                    float v[3] = {
                        mix(lv[0], rv[0], lr),
                        mix(lv[1], rv[1], lr),
                        mix(lv[2], rv[2], lr)
                    };
                    if (median(v[0], v[1], v[2]) == v[i]) {
                        newIntersections[newIntersectionCount].x = (l+lr+.5)/scale.x-translate.x;
                        newIntersections[newIntersectionCount].direction = sign(rv[i]-lv[i]);
                        ++newIntersectionCount;
                    }
                }
            }
        }
        // Sort new intersections
        if (newIntersectionCount >= 2) {
            if (newIntersections[0].x > newIntersections[1].x)
                newIntersections[3] = newIntersections[0], newIntersections[0] = newIntersections[1], newIntersections[1] = newIntersections[3];
            if (newIntersectionCount >= 3 && newIntersections[1].x > newIntersections[2].x) {
                newIntersections[3] = newIntersections[1], newIntersections[1] = newIntersections[2], newIntersections[2] = newIntersections[3];
                if (newIntersections[0].x > newIntersections[1].x)
                    newIntersections[3] = newIntersections[0], newIntersections[0] = newIntersections[1], newIntersections[1] = newIntersections[3];
            }
        }
        for (int i = 0; i < newIntersectionCount; ++i) {
            if ((newIntersections[i].direction > 0) == !inside) {
                intersections.push_back(newIntersections[i]);
                inside = !inside;
            }
        }
        // Consistency check
        float rvScalar = median(rv[0], rv[1], rv[2]);
        if ((rvScalar > .5f) != inside && rvScalar != .5f && !intersections.empty()) {
            intersections.pop_back();
            inside = !inside;
        }
    }
#ifdef MSDFGEN_USE_CPP11
    line.setIntersections((std::vector<Scanline::Intersection> &&) intersections);
#else
    line.setIntersections(intersections);
#endif
}

double estimateSDFError(const BitmapConstRef<float, 1> &sdf, const Shape &shape, const Vector2 &scale, const Vector2 &translate, int scanlinesPerRow, FillRule fillRule) {
    if (sdf.width <= 1 || sdf.height <= 1 || scanlinesPerRow < 1)
        return 0;
    double subRowSize = 1./scanlinesPerRow;
    double xFrom = .5/scale.x-translate.x;
    double xTo = (sdf.width-.5)/scale.x-translate.x;
    double overlapFactor = 1/(xTo-xFrom);
    double error = 0;
    Scanline refScanline, sdfScanline;
    for (int row = 0; row < sdf.height-1; ++row) {
        for (int subRow = 0; subRow < scanlinesPerRow; ++subRow) {
            double bt = (subRow+.5)*subRowSize;
            double y = (row+bt+.5)/scale.y-translate.y;
            shape.scanline(refScanline, y);
            scanlineSDF(sdfScanline, sdf, scale, translate, shape.inverseYAxis, y);
            error += 1-overlapFactor*Scanline::overlap(refScanline, sdfScanline, xFrom, xTo, fillRule);
        }
    }
    return error/((sdf.height-1)*scanlinesPerRow);
}

double estimateSDFError(const BitmapConstRef<float, 3> &sdf, const Shape &shape, const Vector2 &scale, const Vector2 &translate, int scanlinesPerRow, FillRule fillRule) {
    if (sdf.width <= 1 || sdf.height <= 1 || scanlinesPerRow < 1)
        return 0;
    double subRowSize = 1./scanlinesPerRow;
    double xFrom = .5/scale.x-translate.x;
    double xTo = (sdf.width-.5)/scale.x-translate.x;
    double overlapFactor = 1/(xTo-xFrom);
    double error = 0;
    Scanline refScanline, sdfScanline;
    for (int row = 0; row < sdf.height-1; ++row) {
        for (int subRow = 0; subRow < scanlinesPerRow; ++subRow) {
            double bt = (subRow+.5)*subRowSize;
            double y = (row+bt+.5)/scale.y-translate.y;
            shape.scanline(refScanline, y);
            scanlineSDF(sdfScanline, sdf, scale, translate, shape.inverseYAxis, y);
            error += 1-overlapFactor*Scanline::overlap(refScanline, sdfScanline, xFrom, xTo, fillRule);
        }
    }
    return error/((sdf.height-1)*scanlinesPerRow);
}

}