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2008857660
Render the confidence area and the regression line into a pixmap and show that using a QSGNode. It is unclear whether it is preferred to do it this way or to triangulate the confidence area into triangles to be drawn by the shader. Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
87 lines
3 KiB
C++
87 lines
3 KiB
C++
// SPDX-License-Identifier: GPL-2.0
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#include "regressionitem.h"
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#include "statsaxis.h"
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#include "zvalues.h"
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#include <cmath>
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static const QColor regressionItemColor(Qt::red);
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static const double regressionLineWidth = 2.0;
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RegressionItem::RegressionItem(StatsView &view, regression_data reg,
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StatsAxis *xAxis, StatsAxis *yAxis) :
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ChartPixmapItem(view, ChartZValue::ChartFeatures),
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xAxis(xAxis), yAxis(yAxis), reg(reg)
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{
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}
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RegressionItem::~RegressionItem()
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{
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}
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void RegressionItem::updatePosition()
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{
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if (!xAxis || !yAxis)
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return;
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auto [minX, maxX] = xAxis->minMax();
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auto [minY, maxY] = yAxis->minMax();
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auto [screenMinX, screenMaxX] = xAxis->minMaxScreen();
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// Draw the confidence interval according to http://www2.stat.duke.edu/~tjl13/s101/slides/unit6lec3H.pdf p.5 with t*=2 for 95% confidence
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QPolygonF poly;
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const int num_samples = 101;
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poly.reserve(num_samples * 2);
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for (int i = 0; i < num_samples; ++i) {
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double x = (maxX - minX) / (num_samples - 1) * static_cast<double>(i) + minX;
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poly << QPointF(xAxis->toScreen(x),
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yAxis->toScreen(reg.a * x + reg.b + 2.0 * sqrt(reg.res2 / (reg.n - 2) * (1.0 / reg.n + (x - reg.xavg) * (x - reg.xavg) / (reg.n - 1) * (reg.n -2) / reg.sx2))));
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}
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for (int i = num_samples - 1; i >= 0; --i) {
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double x = (maxX - minX) / (num_samples - 1) * static_cast<double>(i) + minX;
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poly << QPointF(xAxis->toScreen(x),
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yAxis->toScreen(reg.a * x + reg.b - 2.0 * sqrt(reg.res2 / (reg.n - 2) * (1.0 / reg.n + (x - reg.xavg) * (x - reg.xavg) / (reg.n - 1) * (reg.n -2) / reg.sx2))));
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}
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QPolygonF linePolygon;
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linePolygon.reserve(2);
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linePolygon << QPointF(screenMinX, yAxis->toScreen(reg.a * minX + reg.b));
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linePolygon << QPointF(screenMaxX, yAxis->toScreen(reg.a * maxX + reg.b));
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QRectF box(QPointF(screenMinX, yAxis->toScreen(minY)), QPointF(screenMaxX, yAxis->toScreen(maxY)));
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poly = poly.intersected(box);
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linePolygon = linePolygon.intersected(box);
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if (poly.size() < 2 || linePolygon.size() < 2)
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return;
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// Find lowest and highest point on screen. In principle, we need
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// only check half of the polygon, but let's not optimize without reason.
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double screenMinY = std::numeric_limits<double>::max();
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double screenMaxY = std::numeric_limits<double>::lowest();
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for (const QPointF &point: poly) {
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double y = point.y();
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if (y < screenMinY)
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screenMinY = y;
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if (y > screenMaxY)
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screenMaxY = y;
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}
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screenMinY = floor(screenMinY - 1.0);
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screenMaxY = ceil(screenMaxY + 1.0);
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QPointF offset(screenMinX, screenMinY);
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for (QPointF &point: poly)
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point -= offset;
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for (QPointF &point: linePolygon)
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point -= offset;
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ChartPixmapItem::resize(QSizeF(screenMaxX - screenMinX, screenMaxY - screenMinY));
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img->fill(Qt::transparent);
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QColor col(regressionItemColor);
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col.setAlphaF(reg.r2);
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painter->setPen(Qt::NoPen);
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painter->setBrush(QBrush(col));
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painter->drawPolygon(poly);
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painter->setPen(QPen(regressionItemColor, regressionLineWidth));
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painter->drawLine(QPointF(linePolygon[0]), QPointF(linePolygon[1]));
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ChartPixmapItem::setPos(offset);
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}
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