MapLibreParticleLab/src/mbgl/map/transform_state.cpp

#include <mbgl/map/transform_state.hpp>
#include <mbgl/map/tile_id.hpp>
#include <mbgl/util/constants.hpp>
#include <mbgl/util/interpolate.hpp>
#include <mbgl/util/math.hpp>

namespace mbgl {

TransformState::TransformState(ConstrainMode constrainMode_)
    : constrainMode(constrainMode_)
{
}

#pragma mark - Matrix

void TransformState::matrixFor(mat4& matrix, const TileID& id, const int8_t z) const {
    const double tile_scale = std::pow(2, z);
    double s = worldSize() / tile_scale;

    matrix::identity(matrix);
    matrix::translate(matrix, matrix, id.x * s, id.y * s, 0);
    matrix::scale(matrix, matrix, s / util::EXTENT, s / util::EXTENT, 1);
}

void TransformState::getProjMatrix(mat4& projMatrix) const {
    double halfFov = std::atan(0.5 / getAltitude());
    double topHalfSurfaceDistance = std::sin(halfFov) * getAltitude() /
        std::sin(M_PI / 2.0f - getPitch() - halfFov);
    // Calculate z value of the farthest fragment that should be rendered.
    double farZ = std::cos(M_PI / 2.0f - getPitch()) * topHalfSurfaceDistance + getAltitude();

    matrix::perspective(projMatrix, 2.0f * std::atan((getHeight() / 2.0f) / getAltitude()),
            double(getWidth()) / getHeight(), 0.1, farZ);

    matrix::translate(projMatrix, projMatrix, 0, 0, -getAltitude());

    // After the rotateX, z values are in pixel units. Convert them to
    // altitude unites. 1 altitude unit = the screen height.
    matrix::scale(projMatrix, projMatrix, 1, -1, 1.0f / (rotatedNorth() ? getWidth() : getHeight()));

    using NO = NorthOrientation;
    switch (getNorthOrientation()) {
        case NO::Rightwards: matrix::rotate_y(projMatrix, projMatrix, getPitch()); break;
        case NO::Downwards: matrix::rotate_x(projMatrix, projMatrix, -getPitch()); break;
        case NO::Leftwards: matrix::rotate_y(projMatrix, projMatrix, -getPitch()); break;
        default: matrix::rotate_x(projMatrix, projMatrix, getPitch()); break;
    }

    matrix::rotate_z(projMatrix, projMatrix, getAngle() + getNorthOrientationAngle());

    matrix::translate(projMatrix, projMatrix, pixel_x() - getWidth() / 2.0f,
            pixel_y() - getHeight() / 2.0f, 0);
}

#pragma mark - Dimensions

uint16_t TransformState::getWidth() const {
    return width;
}

uint16_t TransformState::getHeight() const {
    return height;
}

#pragma mark - North Orientation

NorthOrientation TransformState::getNorthOrientation() const {
    return orientation;
}

double TransformState::getNorthOrientationAngle() const {
    double angleOrientation = 0;
    if (orientation == NorthOrientation::Rightwards) {
        angleOrientation += M_PI / 2.0f;
    } else if (orientation == NorthOrientation::Downwards) {
        angleOrientation += M_PI;
    } else if (orientation == NorthOrientation::Leftwards) {
        angleOrientation -= M_PI / 2.0f;
    }
    return angleOrientation;
}

#pragma mark - Constrain mode

ConstrainMode TransformState::getConstrainMode() const {
    return constrainMode;
}

#pragma mark - Position

LatLng TransformState::getLatLng(LatLng::WrapMode wrapMode) const {
    return {
        util::RAD2DEG * (2 * std::atan(std::exp(y / Cc)) - 0.5 * M_PI),
        -x / Bc,
        wrapMode
    };
}

double TransformState::pixel_x() const {
    const double center = (width - worldSize()) / 2;
    return center + x;
}

double TransformState::pixel_y() const {
    const double center = (height - worldSize()) / 2;
    return center + y;
}

#pragma mark - Zoom

double TransformState::getZoom() const {
    return std::log(scale) / M_LN2;
}

int32_t TransformState::getIntegerZoom() const {
    return std::floor(getZoom());
}

double TransformState::getZoomFraction() const {
    return getZoom() - getIntegerZoom();
}

double TransformState::getScale() const {
    return scale;
}

void TransformState::setMinZoom(const double minZoom) {
    if (minZoom <= getMaxZoom()) {
        min_scale = zoomScale(util::clamp(minZoom, util::MIN_ZOOM, util::MAX_ZOOM));
    }
}

double TransformState::getMinZoom() const {
    double test_scale = min_scale;
    double unused_x = x;
    double unused_y = y;
    constrain(test_scale, unused_x, unused_y);

    return scaleZoom(test_scale);
}

void TransformState::setMaxZoom(const double maxZoom) {
    if (maxZoom >= getMinZoom()) {
        max_scale = zoomScale(util::clamp(maxZoom, util::MIN_ZOOM, util::MAX_ZOOM));
    }
}

double TransformState::getMaxZoom() const {
    return scaleZoom(max_scale);
}


#pragma mark - Rotation

float TransformState::getAngle() const {
    return angle;
}

float TransformState::getAltitude() const {
    return altitude;
}

float TransformState::getPitch() const {
    return pitch;
}


#pragma mark - State

bool TransformState::isChanging() const {
    return rotating || scaling || panning || gestureInProgress;
}

bool TransformState::isRotating() const {
    return rotating;
}

bool TransformState::isScaling() const {
    return scaling;
}

bool TransformState::isPanning() const {
    return panning;
}

bool TransformState::isGestureInProgress() const {
    return gestureInProgress;
}


#pragma mark - Projection

double TransformState::lngX(double lng) const {
    return (util::LONGITUDE_MAX + lng) * worldSize() / util::DEGREES_MAX;
}

double TransformState::latY(double lat) const {
    double y_ = util::RAD2DEG * std::log(std::tan(M_PI / 4 + lat * M_PI / util::DEGREES_MAX));
    return (util::LONGITUDE_MAX - y_) * worldSize() / util::DEGREES_MAX;
}

double TransformState::xLng(double x_, double worldSize_) const {
    return x_ * util::DEGREES_MAX / worldSize_ - util::LONGITUDE_MAX;
}

double TransformState::yLat(double y_, double worldSize_) const {
    double y2 = util::LONGITUDE_MAX - y_ * util::DEGREES_MAX / worldSize_;
    return util::DEGREES_MAX / M_PI * std::atan(std::exp(y2 * util::DEG2RAD)) - 90.0f;
}

double TransformState::zoomScale(double zoom) const {
    return std::pow(2.0f, zoom);
}

double TransformState::scaleZoom(double s) const {
    return ::log2(s);
}

double TransformState::worldSize() const {
    return scale * util::tileSize;
}

ScreenCoordinate TransformState::latLngToScreenCoordinate(const LatLng& latLng) const {
    mat4 mat = coordinatePointMatrix(getZoom());
    vec4<double> p;
    vec4<double> c = { lngX(latLng.longitude) / util::tileSize, latY(latLng.latitude) / util::tileSize, 0, 1 };
    matrix::transformMat4(p, c, mat);
    return { p.x / p.w, height - p.y / p.w };
}

LatLng TransformState::screenCoordinateToLatLng(const ScreenCoordinate& point, LatLng::WrapMode wrapMode) const {
    float targetZ = 0;
    mat4 mat = coordinatePointMatrix(getZoom());

    mat4 inverted;
    bool err = matrix::invert(inverted, mat);

    if (err) throw std::runtime_error("failed to invert coordinatePointMatrix");

    double flippedY = height - point.y;

    // since we don't know the correct projected z value for the point,
    // unproject two points to get a line and then find the point on that
    // line with z=0

    vec4<double> coord0;
    vec4<double> coord1;
    vec4<double> point0 = { point.x, flippedY, 0, 1 };
    vec4<double> point1 = { point.x, flippedY, 1, 1 };
    matrix::transformMat4(coord0, point0, inverted);
    matrix::transformMat4(coord1, point1, inverted);

    double w0 = coord0.w;
    double w1 = coord1.w;
    double x0 = coord0.x / w0;
    double x1 = coord1.x / w1;
    double y0 = coord0.y / w0;
    double y1 = coord1.y / w1;
    double z0 = coord0.z / w0;
    double z1 = coord1.z / w1;

    double t = z0 == z1 ? 0 : (targetZ - z0) / (z1 - z0);
    return {
        yLat(util::interpolate(y0, y1, t), scale),
        xLng(util::interpolate(x0, x1, t), scale),
        wrapMode
    };
}

mat4 TransformState::coordinatePointMatrix(double z) const {
    mat4 proj;
    getProjMatrix(proj);
    float s = worldSize() / std::pow(2, z);
    matrix::scale(proj, proj, s, s, 1);
    matrix::multiply(proj, getPixelMatrix(), proj);
    return proj;
}

mat4 TransformState::getPixelMatrix() const {
    mat4 m;
    matrix::identity(m);
    matrix::scale(m, m, width / 2.0f, -height / 2.0f, 1);
    matrix::translate(m, m, 1, -1, 0);
    return m;
}


#pragma mark - (private helper functions)

bool TransformState::rotatedNorth() const {
    using NO = NorthOrientation;
    return (orientation == NO::Leftwards || orientation == NO::Rightwards);
}

void TransformState::constrain(double& scale_, double& x_, double& y_) const {
    // Constrain minimum scale to avoid zooming out far enough to show off-world areas.
    scale_ = util::max(scale_,
                       static_cast<double>((rotatedNorth() ? height : width) / util::tileSize),
                       static_cast<double>((rotatedNorth() ? width : height) / util::tileSize));

    // Constrain min/max pan to avoid showing off-world areas.
    if (constrainMode == ConstrainMode::WidthAndHeight) {
        double max_x = (scale_ * util::tileSize - (rotatedNorth() ? height : width)) / 2;
        x_ = std::max(-max_x, std::min(x_, max_x));
    }

    if (constrainMode != ConstrainMode::None) {
        double max_y = (scale_ * util::tileSize - (rotatedNorth() ? width : height)) / 2;
        y_ = std::max(-max_y, std::min(y_, max_y));
    }
}

void TransformState::moveLatLng(const LatLng& latLng, const ScreenCoordinate& anchor) {
    if (!latLng || !anchor) return;

    auto latLngToTileCoord = [&](const LatLng& ll) -> vec2<double> {
        return { lngX(ll.longitude), latY(ll.latitude) };
    };

    auto tileCoordToLatLng = [&](const vec2<double> coord) -> LatLng {
        return { yLat(coord.y, worldSize()), xLng(coord.x, worldSize()) };
    };

    auto centerCoord = latLngToTileCoord(getLatLng(LatLng::Unwrapped));
    auto latLngCoord = latLngToTileCoord(latLng);
    auto anchorCoord = latLngToTileCoord(screenCoordinateToLatLng(anchor));
    setLatLngZoom(tileCoordToLatLng(centerCoord + latLngCoord - anchorCoord), getZoom());
}

void TransformState::setLatLngZoom(const LatLng &latLng, double zoom) {
    double newScale = zoomScale(zoom);
    const double newWorldSize = newScale * util::tileSize;
    Bc = newWorldSize / util::DEGREES_MAX;
    Cc = newWorldSize / util::M2PI;
    
    const double m = 1 - 1e-15;
    const double f = util::clamp(std::sin(util::DEG2RAD * latLng.latitude), -m, m);
    
    ScreenCoordinate point = {
        -latLng.longitude * Bc,
        0.5 * Cc * std::log((1 + f) / (1 - f)),
    };
    setScalePoint(newScale, point);
}

void TransformState::setScalePoint(const double newScale, const ScreenCoordinate &point) {
    double constrainedScale = newScale;
    ScreenCoordinate constrainedPoint = point;
    constrain(constrainedScale, constrainedPoint.x, constrainedPoint.y);
    
    scale = constrainedScale;
    x = constrainedPoint.x;
    y = constrainedPoint.y;
    Bc = worldSize() / util::DEGREES_MAX;
    Cc = worldSize() / util::M2PI;
}

} // namespace mbgl