qemby/src/qEmbyApp/utils/shadowpixmap.cpp

#include "shadowpixmap.h"

#include <QDir>
#include <QGraphicsBlurEffect>
#include <QGraphicsPixmapItem>
#include <QGraphicsScene>
#include <QImage>
#include <QPainter>
#include <QStandardPaths>

namespace
{
// Width of the uniform, stretchable interior between the rounded corners.
// Kept small (the centre is a flat solid colour, so 4 logical px is plenty).
constexpr int kCenter = 4;

int borderFor(int blurRadius, int cornerRadius)
{
    // Falloff reach beyond the object edge, plus the corner radius which lives
    // inside the fixed (non-stretched) border so corners never distort.
    return (blurRadius + 1) + cornerRadius;
}

int totalFor(int blurRadius, int cornerRadius)
{
    return 2 * borderFor(blurRadius, cornerRadius) + kCenter;
}

QString cacheFilePath(int blurRadius, int cornerRadius, const QColor &color, qreal dpr)
{
    const QString dir =
        QStandardPaths::writableLocation(QStandardPaths::CacheLocation) + "/shadows";
    QDir().mkpath(dir);
    // dpr folded in at x100 so e.g. 1.5 -> 150; colour as rrggbbaa.
    const QString name = QString("shadow_b%1_c%2_%3_d%4.png")
                             .arg(blurRadius)
                             .arg(cornerRadius)
                             .arg(static_cast<uint>(color.rgba()), 8, 16, QLatin1Char('0'))
                             .arg(qRound(dpr * 100));
    return dir + '/' + name;
}

// Render the rounded rect, then blur it off-screen via QGraphicsBlurEffect.
// Done once per cache key; the cost here is irrelevant to runtime frame rate.
QImage bake(int blurRadius, int cornerRadius, const QColor &color, qreal dpr)
{
    const int total = totalFor(blurRadius, cornerRadius);
    const int border = borderFor(blurRadius, cornerRadius);
    const qreal s = dpr;
    const int physTotal = qMax(1, qRound(total * s));

    QImage shape(physTotal, physTotal, QImage::Format_ARGB32_Premultiplied);
    shape.fill(Qt::transparent);
    {
        QPainter p(&shape);
        p.setRenderHint(QPainter::Antialiasing, true);
        p.setPen(Qt::NoPen);
        p.setBrush(color);
        // Object footprint: inset by the falloff reach (border - corner) so the
        // blur has room to fade on every side.
        const qreal reach = (border - cornerRadius) * s;
        const qreal objSide = (total - 2 * (border - cornerRadius)) * s;
        p.drawRoundedRect(QRectF(reach, reach, objSide, objSide),
                          cornerRadius * s, cornerRadius * s);
    }

    QGraphicsScene scene;
    auto *item = scene.addPixmap(QPixmap::fromImage(shape));
    auto *blur = new QGraphicsBlurEffect;
    blur->setBlurRadius(blurRadius * s);
    blur->setBlurHints(QGraphicsBlurEffect::QualityHint);
    item->setGraphicsEffect(blur);

    QImage out(physTotal, physTotal, QImage::Format_ARGB32_Premultiplied);
    out.fill(Qt::transparent);
    {
        QPainter op(&out);
        scene.render(&op, QRectF(0, 0, physTotal, physTotal),
                     QRectF(0, 0, physTotal, physTotal));
    }
    return out;
}
} // namespace

namespace ShadowPixmap
{
NinePatchShadow make(int blurRadius, int cornerRadius, const QColor &color, qreal dpr)
{
    NinePatchShadow result;
    result.border = borderFor(blurRadius, cornerRadius);
    result.total = totalFor(blurRadius, cornerRadius);
    result.dpr = dpr;

    const QString path = cacheFilePath(blurRadius, cornerRadius, color, dpr);

    QPixmap cached;
    if (cached.load(path, "PNG") && !cached.isNull())
    {
        result.pixmap = cached;
        return result;
    }

    const QImage baked = bake(blurRadius, cornerRadius, color, dpr);
    result.pixmap = QPixmap::fromImage(baked);
    baked.save(path, "PNG"); // best-effort cache; failure just re-bakes next time
    return result;
}

void drawNinePatch(QPainter *painter, const QRect &target, const NinePatchShadow &patch)
{
    if (!painter || patch.isNull())
    {
        return;
    }

    const int b = patch.border;
    const int t = patch.total;
    const qreal s = patch.dpr;
    const QRect r = target;

    // Degenerate target (smaller than the two fixed borders): nothing sensible
    // to slice, skip rather than draw garbage.
    if (r.width() < 2 * b || r.height() < 2 * b)
    {
        return;
    }

    // 3x3 grid: corners fixed, edges/centre stretched. Target columns/rows are
    // logical; source columns/rows are physical (pixmap carries no dpr).
    const int xt[4] = {r.left(), r.left() + b, r.right() + 1 - b, r.right() + 1};
    const int yt[4] = {r.top(), r.top() + b, r.bottom() + 1 - b, r.bottom() + 1};
    const qreal xs[4] = {0.0, b * s, (t - b) * s, t * s};
    const qreal ys[4] = {0.0, b * s, (t - b) * s, t * s};

    for (int i = 0; i < 3; ++i)
    {
        for (int j = 0; j < 3; ++j)
        {
            const QRectF targetCell(xt[i], yt[j], xt[i + 1] - xt[i], yt[j + 1] - yt[j]);
            const QRectF sourceCell(xs[i], ys[j], xs[i + 1] - xs[i], ys[j + 1] - ys[j]);
            painter->drawPixmap(targetCell, patch.pixmap, sourceCell);
        }
    }
}
} // namespace ShadowPixmap