custominstancing.cpp

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++ // Copyright (C) 2020 The Qt Company Ltd.

++ // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only

++

++ #include "custominstancing.h"

++ #include <math.h>

++ #include <QMatrix4x4>

++

++ struct InstanceTableEntry {

++     QVector4D row0;

++     QVector4D row1;

++     QVector4D row2;

++     QVector4D color;

++     QVector4D instanceData;

++ };

++

++ void CustomInstancing::setInstanceCount(int instanceCount)

++ {

++     if (m_instanceCount == instanceCount)

++         return;

++

++     m_instanceCount = instanceCount;

++     emit instanceCountChanged(m_instanceCount);

++ }

++

++ QByteArray CustomInstancing::getInstanceBuffer(int *instanceCount)

++ {

++     QByteArray instanceData;

++     if (instanceCount)

++         *instanceCount = m_instanceCount;

++     if (m_instanceCount == 0)

++         return instanceData;

++

++     instanceData.resize(m_instanceCount * 20 * sizeof(float));

++     auto array = reinterpret_cast<InstanceTableEntry*>(instanceData.data());

++

++     const int rows = floor(sqrt(m_instanceCount));

++     const int columns = m_instanceCount/rows;

++

++     for (int i = 0; i < m_instanceCount; ++i) {

++         QMatrix4x4 xform;

++

++         int ix = i % columns;

++         int iy = i / columns;

++         float x = 100.0 * (ix - columns/2);

++         float y = 100.0 * (iy - rows/2);

++         float z = (x*x + y*y)/1000;

++

++         xform(0, 3) += x;

++         xform(1, 3) += y;

++         xform(2, 3) += z;

++

++         float scale = 0.75;

++         xform(0, 0) = scale;

++         xform(1, 1) = scale;

++         xform(2, 2) = scale;

++

++         QVector4D color(float(ix)/columns, float(iy)/columns, 1.0, float(i) / m_instanceCount);

++

++         array[i] = {

++             xform.row(0),

++             xform.row(1),

++             xform.row(2),

++             color,

++             {}

++         };

++     }

++

++     return instanceData;

++ }