351 lines
11 KiB
C++
351 lines
11 KiB
C++
/*
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* SPDX-FileCopyrightText: 2018 Vlad Zahorodnii <vlad.zahorodnii@kde.org>
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*
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* The box blur implementation is based on AlphaBoxBlur from Firefox.
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*
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* SPDX-License-Identifier: GPL-2.0-or-later
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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// own
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#include "breezeboxshadowrenderer.h"
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// Qt
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#include <QPainter>
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#include <QtMath>
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namespace Breeze
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{
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static inline int calculateBlurRadius(qreal stdDev)
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{
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// See https://www.w3.org/TR/SVG11/filters.html#feGaussianBlurElement
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const qreal gaussianScaleFactor = (3.0 * qSqrt(2.0 * M_PI) / 4.0) * 1.5;
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return qMax(2, qFloor(stdDev * gaussianScaleFactor + 0.5));
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}
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static inline qreal calculateBlurStdDev(int radius)
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{
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// See https://www.w3.org/TR/css-backgrounds-3/#shadow-blur
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return radius * 0.5;
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}
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static inline QSize calculateBlurExtent(int radius)
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{
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const int blurRadius = calculateBlurRadius(calculateBlurStdDev(radius));
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return QSize(blurRadius, blurRadius);
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}
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struct BoxLobes
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{
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int left; ///< how many pixels sample to the left
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int right; ///< how many pixels sample to the right
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};
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/**
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* Compute box filter parameters.
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*
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* @param radius The blur radius.
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* @returns Parameters for three box filters.
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**/
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static QVector<BoxLobes> computeLobes(int radius)
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{
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const int blurRadius = calculateBlurRadius(calculateBlurStdDev(radius));
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const int z = blurRadius / 3;
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int major;
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int minor;
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int final;
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switch (blurRadius % 3) {
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case 0:
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major = z;
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minor = z;
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final = z;
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break;
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case 1:
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major = z + 1;
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minor = z;
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final = z;
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break;
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case 2:
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major = z + 1;
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minor = z;
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final = z + 1;
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break;
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default:
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Q_UNREACHABLE();
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}
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Q_ASSERT(major + minor + final == blurRadius);
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return {
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{major, minor},
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{minor, major},
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{final, final}
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};
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}
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/**
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* Process a row with a box filter.
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*
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* @param src The start of the row.
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* @param dst The destination.
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* @param width The width of the row, in pixels.
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* @param horizontalStride The number of bytes from one alpha value to the
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* next alpha value.
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* @param verticalStride The number of bytes from one row to the next row.
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* @param lobes Params of the box filter.
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* @param transposeInput Whether the input is transposed.
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* @param transposeOutput Whether the output should be transposed.
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**/
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static inline void boxBlurRowAlpha(const uint8_t *src, uint8_t *dst, int width, int horizontalStride,
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int verticalStride, const BoxLobes &lobes, bool transposeInput,
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bool transposeOutput)
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{
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const int inputStep = transposeInput ? verticalStride : horizontalStride;
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const int outputStep = transposeOutput ? verticalStride : horizontalStride;
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const int boxSize = lobes.left + 1 + lobes.right;
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const int reciprocal = (1 << 24) / boxSize;
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uint32_t alphaSum = (boxSize + 1) / 2;
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const uint8_t *left = src;
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const uint8_t *right = src;
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uint8_t *out = dst;
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const uint8_t firstValue = src[0];
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const uint8_t lastValue = src[(width - 1) * inputStep];
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alphaSum += firstValue * lobes.left;
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const uint8_t *initEnd = src + (boxSize - lobes.left) * inputStep;
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while (right < initEnd) {
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alphaSum += *right;
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right += inputStep;
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}
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const uint8_t *leftEnd = src + boxSize * inputStep;
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while (right < leftEnd) {
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*out = (alphaSum * reciprocal) >> 24;
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alphaSum += *right - firstValue;
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right += inputStep;
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out += outputStep;
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}
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const uint8_t *centerEnd = src + width * inputStep;
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while (right < centerEnd) {
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*out = (alphaSum * reciprocal) >> 24;
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alphaSum += *right - *left;
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left += inputStep;
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right += inputStep;
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out += outputStep;
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}
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const uint8_t *rightEnd = dst + width * outputStep;
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while (out < rightEnd) {
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*out = (alphaSum * reciprocal) >> 24;
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alphaSum += lastValue - *left;
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left += inputStep;
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out += outputStep;
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}
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}
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/**
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* Blur the alpha channel of a given image.
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*
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* @param image The input image.
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* @param radius The blur radius.
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* @param rect Specifies what part of the image to blur. If nothing is provided, then
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* the whole alpha channel of the input image will be blurred.
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**/
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static inline void boxBlurAlpha(QImage &image, int radius, const QRect &rect = {})
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{
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if (radius < 2) {
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return;
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}
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const QVector<BoxLobes> lobes = computeLobes(radius);
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const QRect blurRect = rect.isNull() ? image.rect() : rect;
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const int alphaOffset = QSysInfo::ByteOrder == QSysInfo::BigEndian ? 0 : 3;
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const int width = blurRect.width();
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const int height = blurRect.height();
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const int rowStride = image.bytesPerLine();
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const int pixelStride = image.depth() >> 3;
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const int bufferStride = qMax(width, height) * pixelStride;
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QScopedPointer<uint8_t, QScopedPointerArrayDeleter<uint8_t> > buf(new uint8_t[2 * bufferStride]);
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uint8_t *buf1 = buf.data();
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uint8_t *buf2 = buf1 + bufferStride;
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// Blur the image in horizontal direction.
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for (int i = 0; i < height; ++i) {
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uint8_t *row = image.scanLine(blurRect.y() + i) + blurRect.x() * pixelStride + alphaOffset;
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boxBlurRowAlpha(row, buf1, width, pixelStride, rowStride, lobes[0], false, false);
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boxBlurRowAlpha(buf1, buf2, width, pixelStride, rowStride, lobes[1], false, false);
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boxBlurRowAlpha(buf2, row, width, pixelStride, rowStride, lobes[2], false, false);
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}
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// Blur the image in vertical direction.
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for (int i = 0; i < width; ++i) {
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uint8_t *column = image.scanLine(blurRect.y()) + (blurRect.x() + i) * pixelStride + alphaOffset;
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boxBlurRowAlpha(column, buf1, height, pixelStride, rowStride, lobes[0], true, false);
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boxBlurRowAlpha(buf1, buf2, height, pixelStride, rowStride, lobes[1], false, false);
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boxBlurRowAlpha(buf2, column, height, pixelStride, rowStride, lobes[2], false, true);
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}
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}
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static inline void mirrorTopLeftQuadrant(QImage &image)
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{
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const int width = image.width();
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const int height = image.height();
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const int centerX = qCeil(width * 0.5);
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const int centerY = qCeil(height * 0.5);
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const int alphaOffset = QSysInfo::ByteOrder == QSysInfo::BigEndian ? 0 : 3;
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const int stride = image.depth() >> 3;
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for (int y = 0; y < centerY; ++y) {
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uint8_t *in = image.scanLine(y) + alphaOffset;
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uint8_t *out = in + (width - 1) * stride;
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for (int x = 0; x < centerX; ++x, in += stride, out -= stride) {
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*out = *in;
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}
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}
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for (int y = 0; y < centerY; ++y) {
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const uint8_t *in = image.scanLine(y) + alphaOffset;
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uint8_t *out = image.scanLine(width - y - 1) + alphaOffset;
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for (int x = 0; x < width; ++x, in += stride, out += stride) {
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*out = *in;
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}
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}
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}
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static void renderShadow(QPainter *painter, const QRect &rect, qreal borderRadius, const QPoint &offset, int radius, const QColor &color)
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{
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const QSize inflation = calculateBlurExtent(radius);
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const QSize size = rect.size() + 2 * inflation;
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const qreal dpr = painter->device()->devicePixelRatioF();
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QImage shadow(size * dpr, QImage::Format_ARGB32_Premultiplied);
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shadow.setDevicePixelRatio(dpr);
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shadow.fill(Qt::transparent);
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QRect boxRect(QPoint(0, 0), rect.size());
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boxRect.moveCenter(QRect(QPoint(0, 0), size).center());
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const qreal xRadius = 2.0 * borderRadius / boxRect.width();
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const qreal yRadius = 2.0 * borderRadius / boxRect.height();
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QPainter shadowPainter;
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shadowPainter.begin(&shadow);
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shadowPainter.setRenderHint(QPainter::Antialiasing);
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shadowPainter.setPen(Qt::NoPen);
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shadowPainter.setBrush(Qt::black);
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shadowPainter.drawRoundedRect(boxRect, xRadius, yRadius);
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shadowPainter.end();
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// Because the shadow texture is symmetrical, that's enough to blur
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// only the top-left quadrant and then mirror it.
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const QRect blurRect(0, 0, qCeil(shadow.width() * 0.5), qCeil(shadow.height() * 0.5));
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const int scaledRadius = qRound(radius * dpr);
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boxBlurAlpha(shadow, scaledRadius, blurRect);
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mirrorTopLeftQuadrant(shadow);
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// Give the shadow a tint of the desired color.
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shadowPainter.begin(&shadow);
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shadowPainter.setCompositionMode(QPainter::CompositionMode_SourceIn);
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shadowPainter.fillRect(shadow.rect(), color);
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shadowPainter.end();
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// Actually, present the shadow.
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QRect shadowRect = shadow.rect();
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shadowRect.setSize(shadowRect.size() / dpr);
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shadowRect.moveCenter(rect.center() + offset);
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painter->drawImage(shadowRect, shadow);
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}
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void BoxShadowRenderer::setBoxSize(const QSize &size)
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{
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m_boxSize = size;
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}
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void BoxShadowRenderer::setBorderRadius(qreal radius)
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{
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m_borderRadius = radius;
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}
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void BoxShadowRenderer::setDevicePixelRatio(qreal dpr)
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{
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m_dpr = dpr;
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}
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void BoxShadowRenderer::addShadow(const QPoint &offset, int radius, const QColor &color)
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{
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Shadow shadow = {};
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shadow.offset = offset;
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shadow.radius = radius;
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shadow.color = color;
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m_shadows.append(shadow);
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}
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QImage BoxShadowRenderer::render() const
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{
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if (m_shadows.isEmpty()) {
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return {};
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}
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QSize canvasSize;
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for (const Shadow &shadow : qAsConst(m_shadows)) {
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canvasSize = canvasSize.expandedTo(
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calculateMinimumShadowTextureSize(m_boxSize, shadow.radius, shadow.offset));
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}
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QImage canvas(canvasSize * m_dpr, QImage::Format_ARGB32_Premultiplied);
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canvas.setDevicePixelRatio(m_dpr);
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canvas.fill(Qt::transparent);
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QRect boxRect(QPoint(0, 0), m_boxSize);
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boxRect.moveCenter(QRect(QPoint(0, 0), canvasSize).center());
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QPainter painter(&canvas);
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for (const Shadow &shadow : qAsConst(m_shadows)) {
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renderShadow(&painter, boxRect, m_borderRadius, shadow.offset, shadow.radius, shadow.color);
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}
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painter.end();
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return canvas;
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}
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QSize BoxShadowRenderer::calculateMinimumBoxSize(int radius)
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{
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const QSize blurExtent = calculateBlurExtent(radius);
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return 2 * blurExtent + QSize(1, 1);
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}
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QSize BoxShadowRenderer::calculateMinimumShadowTextureSize(const QSize &boxSize, int radius, const QPoint &offset)
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{
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return boxSize + 2 * calculateBlurExtent(radius) + QSize(qAbs(offset.x()), qAbs(offset.y()));
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}
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} // namespace Breeze
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