KisAntiAliasSelectionFilter Class Reference

AntiAlias filter for selections inspired by FXAA. More...

#include <kis_selection_filters.h>

Inheritance diagram for KisAntiAliasSelectionFilter:

Public Member Functions
KUndo2MagicString	name () override
void	process (KisPixelSelectionSP pixelSelection, const QRect &rect) override
Public Member Functions inherited from KisSelectionFilter
virtual QRect	changeRect (const QRect &rect, KisDefaultBoundsBaseSP defaultBounds)
virtual	~KisSelectionFilter ()

Private Member Functions
void	findSpanExtreme (quint8 **scanlines, qint32 x, qint32 pixelOffset, qint32 rowMultiplier, qint32 colMultiplier, qint32 direction, qint32 pixelAvg, qint32 scaledGradient, qint32 currentPixelDiff, qint32 *spanEndDistance, qint32 *pixelDiff, bool *spanExtremeValidType) const
	Get the extreme point of the span for the current pixel in the given direction.
void	findSpanExtremes (quint8 **scanlines, qint32 x, qint32 pixelOffset, qint32 rowMultiplier, qint32 colMultiplier, qint32 pixelAvg, qint32 scaledGradient, qint32 currentPixelDiff, qint32 *negativeSpanEndDistance, qint32 *positiveSpanEndDistance, qint32 *negativePixelDiff, qint32 *positivePixelDiff, bool *negativeSpanExtremeValid, bool *positiveSpanExtremeValid) const
	Get the extreme points of the span for the current pixel.
bool	getInterpolationValue (qint32 negativeSpanEndDistance, qint32 positiveSpanEndDistance, qint32 negativePixelDiff, qint32 positivePixelDiff, qint32 currentPixelDiff, bool negativeSpanExtremeValid, bool positiveSpanExtremeValid, qint32 *interpolationValue) const
	Get a interpolation value to linearly interpolate the current pixel with its edge neighbor.

Static Private Attributes
static constexpr qint32	currentScanlineIndex {verticalBorderSize}
	Offset of the current scanline in the buffer (The middle scanline).
static constexpr qint32	edgeThreshold {4}
	Edges with gradient less than this value will not be antiAliased.
static constexpr qint32	horizontalBorderSize {2}
	The size of the border added internally to the left and right of the scanline buffer so that we can read outside the selection rect without problems. It must be equal to the largest value in offsets.
static constexpr qint32	numberOfScanlines {2 * verticalBorderSize + 1}
	Number of scanlines in the internal buffer.
static constexpr qint32	numSteps {30}
	Number of steps to jump when searching for one of the ends of the antiAliased span.
static constexpr qint32	offsets [numSteps]
	This array of numSteps size holds the number of pixels to jump in each step.
static constexpr qint32	verticalBorderSize {40}
	The size of the border added internally to the top and bottom of the scanline buffer so that we can read outside the selection rect without problems. It must be equal to the sum of all values in offsets.

Additional Inherited Members
Protected Member Functions inherited from KisSelectionFilter
void	computeBorder (qint32 *circ, qint32 xradius, qint32 yradius)
void	computeTransition (quint8 *transition, quint8 **buf, qint32 width)
void	rotatePointers (quint8 **p, quint32 n)

Detailed Description

AntiAlias filter for selections inspired by FXAA.

Definition at line 147 of file kis_selection_filters.h.

Member Function Documentation

findSpanExtreme()

void KisAntiAliasSelectionFilter::findSpanExtreme ( quint8 ** scanlines, qint32 x, qint32 pixelOffset, qint32 rowMultiplier, qint32 colMultiplier, qint32 direction, qint32 pixelAvg, qint32 scaledGradient, qint32 currentPixelDiff, qint32 * spanEndDistance, qint32 * pixelDiff, bool * spanExtremeValidType ) const

private

Get the extreme point of the span for the current pixel in the given direction.

Definition at line 974 of file kis_selection_filters.cpp.

{
    *spanEndDistance = 0;
    *spanExtremeValid = true;
    for (qint32 i = 0; i < numSteps; ++i) {
        *spanEndDistance += offsets[i];
        const qint32 row1 = currentScanlineIndex + (direction * *spanEndDistance * rowMultiplier);
        const qint32 col1 = x + horizontalBorderSize + (direction * *spanEndDistance * colMultiplier);
        const qint32 row2 = row1 + pixelOffset * colMultiplier;
        const qint32 col2 = col1 + pixelOffset * rowMultiplier;
        const quint8 *pixel1 = scanlines[row1] + col1;
        const quint8 *pixel2 = scanlines[row2] + col2;
        // Get how different are these edge pixels from the current pixels and
        // stop searching if they are too different
        *pixelDiff = ((*pixel1 + *pixel2) >> 1) - pixelAvg;
        if (qAbs(*pixelDiff) > scaledGradient) {
            // If this is the end of the span then check if the corner belongs
            // to a jagged border or to a right angled part of the shape
            qint32 pixelDiff2;
            if ((currentPixelDiff < 0 && *pixelDiff < 0) || (currentPixelDiff > 0 && *pixelDiff > 0)) {
                const qint32 row3 = row2 + pixelOffset * colMultiplier;
                const qint32 col3 = col2 + pixelOffset * rowMultiplier;
                const quint8 *pixel3 = scanlines[row3] + col3;
                pixelDiff2 = ((*pixel2 + *pixel3) >> 1) - pixelAvg;
            } else {
                const qint32 row3 = row1 - pixelOffset * colMultiplier;
                const qint32 col3 = col1 - pixelOffset * rowMultiplier;
                const quint8 *pixel3 = scanlines[row3] + col3;
                pixelDiff2 = ((*pixel1 + *pixel3) >> 1) - pixelAvg;
            }
            *spanExtremeValid = !(qAbs(pixelDiff2) > scaledGradient);
            break;
        }
    }
}

References currentScanlineIndex, horizontalBorderSize, numSteps, and offsets.

findSpanExtremes()

void KisAntiAliasSelectionFilter::findSpanExtremes ( quint8 ** scanlines, qint32 x, qint32 pixelOffset, qint32 rowMultiplier, qint32 colMultiplier, qint32 pixelAvg, qint32 scaledGradient, qint32 currentPixelDiff, qint32 * negativeSpanEndDistance, qint32 * positiveSpanEndDistance, qint32 * negativePixelDiff, qint32 * positivePixelDiff, bool * negativeSpanExtremeValid, bool * positiveSpanExtremeValid ) const

private

Get the extreme points of the span for the current pixel.

Definition at line 1013 of file kis_selection_filters.cpp.

{
    findSpanExtreme(scanlines, x, pixelOffset, rowMultiplier, colMultiplier, -1, pixelAvg, scaledGradient,
                    currentPixelDiff, negativeSpanEndDistance, negativePixelDiff, negativeSpanExtremeValid);
    findSpanExtreme(scanlines, x, pixelOffset, rowMultiplier, colMultiplier, 1, pixelAvg, scaledGradient,
                    currentPixelDiff, positiveSpanEndDistance, positivePixelDiff, positiveSpanExtremeValid);
}

References findSpanExtreme().

getInterpolationValue()

bool KisAntiAliasSelectionFilter::getInterpolationValue ( qint32 negativeSpanEndDistance, qint32 positiveSpanEndDistance, qint32 negativePixelDiff, qint32 positivePixelDiff, qint32 currentPixelDiff, bool negativeSpanExtremeValid, bool positiveSpanExtremeValid, qint32 * interpolationValue ) const

private

Get a interpolation value to linearly interpolate the current pixel with its edge neighbor.

Returns

true if we must apply the interpolation. false otherwise.

Definition at line 933 of file kis_selection_filters.cpp.

{
    // Since we search a limited number of steps in each direction of the
    // current pixel, the end pixel of the span may still belong to the edge.
    // So we check for that, and if that's the case we must not smooth the
    // current pixel 
    const bool pixelDiffLessThanZero = currentPixelDiff < 0;
    quint32 distance;
    if (negativeSpanEndDistance < positiveSpanEndDistance) {
        if (!negativeSpanExtremeValid) {
            return false;
        }
        // The pixel is closer to the negative end
        const bool spanEndPixelDiffLessThanZero = negativePixelDiff < 0;
        if (pixelDiffLessThanZero == spanEndPixelDiffLessThanZero) {
            return false;
        }
        distance = negativeSpanEndDistance;
    } else {
        if (!positiveSpanExtremeValid) {
            return false;
        }
        // The pixel is closer to the positive end
        const bool spanEndPixelDiffLessThanZero = positivePixelDiff < 0;
        if (pixelDiffLessThanZero == spanEndPixelDiffLessThanZero) {
            return false;
        }
        distance = positiveSpanEndDistance;
    }
    const qint32 spanLength = positiveSpanEndDistance + negativeSpanEndDistance;
    *interpolationValue = ((distance << 8) / spanLength) + 128;
    return *interpolationValue >= 0;
}

References distance().

name()

KUndo2MagicString KisAntiAliasSelectionFilter::name ( )

overridevirtual

Reimplemented from KisSelectionFilter.

Definition at line 928 of file kis_selection_filters.cpp.

{
    return kundo2_i18n("Anti-Alias Selection");
}

References kundo2_i18n().

process()

void KisAntiAliasSelectionFilter::process ( KisPixelSelectionSP pixelSelection, const QRect & rect )

overridevirtual

Implements KisSelectionFilter.

Definition at line 1026 of file kis_selection_filters.cpp.

{
    const quint8 defaultPixel = *pixelSelection->defaultPixel().data();
    // Size of a scanline
    const quint32 bytesPerScanline = rect.width() + 2 * horizontalBorderSize;
    // Size of a scanline padded to a multiple of 8
    const quint32 bytesPerPaddedScanline = ((bytesPerScanline + 7) / 8) * 8;
 
    // This buffer contains the number of consecutive scanlines needed to
    // process the current scanline
    QVector<quint8> buffer(bytesPerPaddedScanline * numberOfScanlines);
 
    // These pointers point to the individual scanlines in the buffer
    quint8 *scanlines[numberOfScanlines];
    for (quint32 i = 0; i < numberOfScanlines; ++i) {
        scanlines[i] = buffer.data() + i * bytesPerPaddedScanline;
    }
 
    // Initialize the scanlines
    // Set the border scanlines on the top
    for (qint32 i = 0; i < verticalBorderSize; ++i) {
        memset(scanlines[i], defaultPixel, bytesPerScanline);
    }
    // Copy the first scanlines of the image
    const quint32 numberOfFirstRows = qMin(rect.height(), numberOfScanlines - verticalBorderSize);
    for (quint32 i = verticalBorderSize; i < verticalBorderSize + numberOfFirstRows; ++i) {
        // Set the border pixels on the left
        memset(scanlines[i], defaultPixel, horizontalBorderSize);
        // Copy the pixel data
        pixelSelection->readBytes(scanlines[i] + horizontalBorderSize, rect.x(), rect.y() + i - verticalBorderSize, rect.width(), 1);
        // Set the border pixels on the right
        memset(scanlines[i] + horizontalBorderSize + rect.width(), defaultPixel, horizontalBorderSize);
    }
    // Set the border scanlines on the bottom
    if (verticalBorderSize + numberOfFirstRows < numberOfScanlines) {
        for (quint32 i = verticalBorderSize + numberOfFirstRows; i < numberOfScanlines; ++i) {
            memset(scanlines[i], defaultPixel, bytesPerScanline);
        }
    }
    // Buffer that contains the current output scanline
    QVector<quint8> antialiasedScanline(rect.width());
    // Main loop
    for (int y = 0; y < rect.height(); ++y)
    {
        // Move to the next scanline
        if (y > 0) {
            // Update scanline pointers
            std::rotate(std::begin(scanlines), std::begin(scanlines) + 1, std::end(scanlines));
            // Copy the next scanline
            if (y < rect.height() - verticalBorderSize) {
                // Set the border pixels on the left
                memset(scanlines[numberOfScanlines - 1], defaultPixel, horizontalBorderSize);
                // Copy the pixel data
                pixelSelection->readBytes(scanlines[numberOfScanlines - 1] + horizontalBorderSize, rect.x(), rect.y() + y + verticalBorderSize, rect.width(), 1);
                // Set the border pixels on the right
                memset(scanlines[numberOfScanlines - 1] + horizontalBorderSize + rect.width(), defaultPixel, horizontalBorderSize);
            } else {
                memset(scanlines[numberOfScanlines - 1], defaultPixel, bytesPerScanline);
            }
        }
        // Process the pixels in the current scanline
        for (int x = 0; x < rect.width(); ++x)
        {
            // Get the current pixel and neighbors
            quint8 *pixelPtrM = scanlines[currentScanlineIndex    ] + x + horizontalBorderSize;
            quint8 *pixelPtrN = scanlines[currentScanlineIndex - 1] + x + horizontalBorderSize;
            quint8 *pixelPtrS = scanlines[currentScanlineIndex + 1] + x + horizontalBorderSize;
            const qint32 pixelNW = *(pixelPtrN - 1);
            const qint32 pixelN  = *(pixelPtrN    );
            const qint32 pixelNE = *(pixelPtrN + 1);
            const qint32 pixelW  = *(pixelPtrM - 1);
            const qint32 pixelM  = *(pixelPtrM    );
            const qint32 pixelE  = *(pixelPtrM + 1);
            const qint32 pixelSW = *(pixelPtrS - 1);
            const qint32 pixelS  = *(pixelPtrS    );
            const qint32 pixelSE = *(pixelPtrS + 1);
            // Get the gradients
            const qint32 rowNSum = (pixelNW >> 2) + (pixelN >> 1) + (pixelNE >> 2);
            const qint32 rowMSum = (pixelW  >> 2) + (pixelM >> 1) + (pixelE  >> 2);
            const qint32 rowSSum = (pixelSW >> 2) + (pixelS >> 1) + (pixelSE >> 2);
            const qint32 colWSum = (pixelNW >> 2) + (pixelW >> 1) + (pixelSW >> 2);
            const qint32 colMSum = (pixelN  >> 2) + (pixelM >> 1) + (pixelS  >> 2);
            const qint32 colESum = (pixelNE >> 2) + (pixelE >> 1) + (pixelSE >> 2);
            const qint32 gradientN = qAbs(rowMSum - rowNSum);
            const qint32 gradientS = qAbs(rowSSum - rowMSum);
            const qint32 gradientW = qAbs(colMSum - colWSum);
            const qint32 gradientE = qAbs(colESum - colMSum);
            // Get the maximum gradient
            const qint32 maxGradientNS = qMax(gradientN, gradientS);
            const qint32 maxGradientWE = qMax(gradientW, gradientE);
            const qint32 maxGradient = qMax(maxGradientNS, maxGradientWE);
            // Return early if the gradient is bellow some threshold (given by
            // the value bellow which the jagged edge is not noticeable)
            if (maxGradient < edgeThreshold) {
                antialiasedScanline[x] = pixelM;
                continue;
            }
            // Collect some info about the pixel and neighborhood
            qint32 neighborPixel, gradient;
            qint32 pixelOffset, rowMultiplier, colMultiplier;
            if (maxGradientNS > maxGradientWE) {
                // Horizontal span
                if (gradientN > gradientS) {
                    // The edge is formed with the top pixel
                    neighborPixel = pixelN;
                    gradient = gradientN;
                    pixelOffset = -1;
                } else {
                    // The edge is formed with the bottom pixel
                    neighborPixel = pixelS;
                    gradient = gradientS;
                    pixelOffset = 1;
                }
                rowMultiplier = 0;
                colMultiplier = 1;
            } else {
                // Vertical span
                if (gradientW > gradientE) {
                    // The edge is formed with the left pixel
                    neighborPixel = pixelW;
                    gradient = gradientW;
                    pixelOffset = -1;
                } else {
                    // The edge is formed with the right pixel
                    neighborPixel = pixelE;
                    gradient = gradientE;
                    pixelOffset = 1;
                }
                rowMultiplier = 1;
                colMultiplier = 0;
            }
            // Find the span extremes
            const qint32 pixelAvg = (neighborPixel + pixelM) >> 1;
            const qint32 currentPixelDiff = pixelM - pixelAvg;
            qint32 negativePixelDiff, positivePixelDiff;
            qint32 negativeSpanEndDistance, positiveSpanEndDistance;
            bool negativeSpanExtremeValid, positiveSpanExtremeValid;
            findSpanExtremes(scanlines, x, pixelOffset,
                             rowMultiplier, colMultiplier,
                             pixelAvg, gradient >> 2, currentPixelDiff,
                             &negativeSpanEndDistance, &positiveSpanEndDistance,
                             &negativePixelDiff, &positivePixelDiff,
                             &negativeSpanExtremeValid, &positiveSpanExtremeValid);
            // Get the interpolation value for this pixel given the span extent
            // and perform linear interpolation between the current pixel and
            // the edge neighbor
            qint32 interpolationValue;
            if (!getInterpolationValue(negativeSpanEndDistance, positiveSpanEndDistance,
                                       negativePixelDiff, positivePixelDiff, currentPixelDiff,
                                       negativeSpanExtremeValid, positiveSpanExtremeValid, &interpolationValue)) {
                antialiasedScanline[x] = pixelM;
            } else {
                antialiasedScanline[x] = neighborPixel + ((pixelM - neighborPixel) * interpolationValue >> 8);
            }
        }
        // Copy the scanline data to the mask
        pixelSelection->writeBytes(antialiasedScanline.data(), rect.x(), rect.y() + y, rect.width(), 1);
    }
}

References currentScanlineIndex, KoColor::data(), KisPaintDevice::defaultPixel(), edgeThreshold, findSpanExtremes(), getInterpolationValue(), horizontalBorderSize, numberOfScanlines, KisPaintDevice::readBytes(), verticalBorderSize, and KisPaintDevice::writeBytes().

Member Data Documentation

currentScanlineIndex

constexpr qint32 KisAntiAliasSelectionFilter::currentScanlineIndex {verticalBorderSize}

staticconstexprprivate

Offset of the current scanline in the buffer (The middle scanline).

Definition at line 191 of file kis_selection_filters.h.

{verticalBorderSize};

edgeThreshold

constexpr qint32 KisAntiAliasSelectionFilter::edgeThreshold {4}

staticconstexprprivate

Edges with gradient less than this value will not be antiAliased.

Definition at line 157 of file kis_selection_filters.h.

{4};

horizontalBorderSize

constexpr qint32 KisAntiAliasSelectionFilter::horizontalBorderSize {2}

staticconstexprprivate

The size of the border added internally to the left and right of the scanline buffer so that we can read outside the selection rect without problems. It must be equal to the largest value in offsets.

Definition at line 177 of file kis_selection_filters.h.

{2};

numberOfScanlines

constexpr qint32 KisAntiAliasSelectionFilter::numberOfScanlines {2 * verticalBorderSize + 1}

staticconstexprprivate

Number of scanlines in the internal buffer.

Definition at line 187 of file kis_selection_filters.h.

{2 * verticalBorderSize + 1};

numSteps

constexpr qint32 KisAntiAliasSelectionFilter::numSteps {30}

staticconstexprprivate

Number of steps to jump when searching for one of the ends of the antiAliased span.

Definition at line 162 of file kis_selection_filters.h.

{30};

offsets

constexpr qint32 KisAntiAliasSelectionFilter::offsets

staticconstexprprivate

Initial value:

{
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        2, 2, 2, 2, 2, 2, 2, 2, 2, 2
    }

This array of numSteps size holds the number of pixels to jump in each step.

Definition at line 167 of file kis_selection_filters.h.

                                              {
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        2, 2, 2, 2, 2, 2, 2, 2, 2, 2
    };

verticalBorderSize

constexpr qint32 KisAntiAliasSelectionFilter::verticalBorderSize {40}

staticconstexprprivate

The size of the border added internally to the top and bottom of the scanline buffer so that we can read outside the selection rect without problems. It must be equal to the sum of all values in offsets.

Definition at line 183 of file kis_selection_filters.h.

{40};

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The documentation for this class was generated from the following files:

• libs/image/kis_selection_filters.h
• libs/image/kis_selection_filters.cpp