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mandelbrot.cpp
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Tue, Feb 11, 16:50

mandelbrot.cpp
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// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2008 Benoit Jacob <jacob.benoit.1@gmail.com>
//
// This Source Code Form is subject to the terms of the Mozilla
// Public License v. 2.0. If a copy of the MPL was not distributed
// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
#include "mandelbrot.h"
#include <iostream>
#include<QtGui/QPainter>
#include<QtGui/QImage>
#include<QtGui/QMouseEvent>
#include<QtCore/QTime>
void MandelbrotWidget::resizeEvent(QResizeEvent *)
{
if(size < width() * height())
{
std::cout << "reallocate buffer" << std::endl;
size = width() * height();
if(buffer) delete[]buffer;
buffer = new unsigned char[4*size];
}
}
template<typename T> struct iters_before_test { enum { ret = 8 }; };
template<> struct iters_before_test<double> { enum { ret = 16 }; };
template<typename Real> void MandelbrotThread::render(int img_width, int img_height)
{
enum { packetSize = Eigen::internal::packet_traits<Real>::size }; // number of reals in a Packet
typedef Eigen::Array<Real, packetSize, 1> Packet; // wrap a Packet as a vector
enum { iters_before_test = iters_before_test<Real>::ret };
max_iter = (max_iter / iters_before_test) * iters_before_test;
const int alignedWidth = (img_width/packetSize)*packetSize;
unsigned char *const buffer = widget->buffer;
const double xradius = widget->xradius;
const double yradius = xradius * img_height / img_width;
const int threadcount = widget->threadcount;
typedef Eigen::Array<Real, 2, 1> Vector2;
Vector2 start(widget->center.x() - widget->xradius, widget->center.y() - yradius);
Vector2 step(2*widget->xradius/img_width, 2*yradius/img_height);
total_iter = 0;
for(int y = id; y < img_height; y += threadcount)
{
int pix = y * img_width;
// for each pixel, we're going to do the iteration z := z^2 + c where z and c are complex numbers,
// starting with z = c = complex coord of the pixel. pzi and pzr denote the real and imaginary parts of z.
// pci and pcr denote the real and imaginary parts of c.
Packet pzi_start, pci_start;
for(int i = 0; i < packetSize; i++) pzi_start[i] = pci_start[i] = start.y() + y * step.y();
for(int x = 0; x < alignedWidth; x += packetSize, pix += packetSize)
{
Packet pcr, pci = pci_start, pzr, pzi = pzi_start, pzr_buf;
for(int i = 0; i < packetSize; i++) pzr[i] = pcr[i] = start.x() + (x+i) * step.x();
// do the iterations. Every iters_before_test iterations we check for divergence,
// in which case we can stop iterating.
int j = 0;
typedef Eigen::Matrix<int, packetSize, 1> Packeti;
Packeti pix_iter = Packeti::Zero(), // number of iteration per pixel in the packet
pix_dont_diverge; // whether or not each pixel has already diverged
do
{
for(int i = 0; i < iters_before_test/4; i++) // peel the inner loop by 4
{
# define ITERATE \
pzr_buf = pzr; \
pzr = pzr.square(); \
pzr -= pzi.square(); \
pzr += pcr; \
pzi = (2*pzr_buf)*pzi; \
pzi += pci;
ITERATE ITERATE ITERATE ITERATE
}
pix_dont_diverge = ((pzr.square() + pzi.square())
.eval() // temporary fix as what follows is not yet vectorized by Eigen
<= Packet::Constant(4))
// the 4 here is not a magic value, it's a math fact that if
// the square modulus is >4 then divergence is inevitable.
.template cast<int>();
pix_iter += iters_before_test * pix_dont_diverge;
j++;
total_iter += iters_before_test * packetSize;
}
while(j < max_iter/iters_before_test && pix_dont_diverge.any()); // any() is not yet vectorized by Eigen
// compute pixel colors
for(int i = 0; i < packetSize; i++)
{
buffer[4*(pix+i)] = 255*pix_iter[i]/max_iter;
buffer[4*(pix+i)+1] = 0;
buffer[4*(pix+i)+2] = 0;
}
}
// if the width is not a multiple of packetSize, fill the remainder in black
for(int x = alignedWidth; x < img_width; x++, pix++)
buffer[4*pix] = buffer[4*pix+1] = buffer[4*pix+2] = 0;
}
return;
}
void MandelbrotThread::run()
{
setTerminationEnabled(true);
double resolution = widget->xradius*2/widget->width();
max_iter = 128;
if(resolution < 1e-4f) max_iter += 128 * ( - 4 - std::log10(resolution));
int img_width = widget->width()/widget->draft;
int img_height = widget->height()/widget->draft;
single_precision = resolution > 1e-7f;
if(single_precision)
render<float>(img_width, img_height);
else
render<double>(img_width, img_height);
}
void MandelbrotWidget::paintEvent(QPaintEvent *)
{
static float max_speed = 0;
long long total_iter = 0;
QTime time;
time.start();
for(int th = 0; th < threadcount; th++)
threads[th]->start(QThread::LowPriority);
for(int th = 0; th < threadcount; th++)
{
threads[th]->wait();
total_iter += threads[th]->total_iter;
}
int elapsed = time.elapsed();
if(draft == 1)
{
float speed = elapsed ? float(total_iter)*1000/elapsed : 0;
max_speed = std::max(max_speed, speed);
std::cout << threadcount << " threads, "
<< elapsed << " ms, "
<< speed << " iters/s (max " << max_speed << ")" << std::endl;
int packetSize = threads[0]->single_precision
? int(Eigen::internal::packet_traits<float>::size)
: int(Eigen::internal::packet_traits<double>::size);
setWindowTitle(QString("resolution ")+QString::number(xradius*2/width(), 'e', 2)
+QString(", %1 iterations per pixel, ").arg(threads[0]->max_iter)
+(threads[0]->single_precision ? QString("single ") : QString("double "))
+QString("precision, ")
+(packetSize==1 ? QString("no vectorization")
: QString("vectorized (%1 per packet)").arg(packetSize)));
}
QImage image(buffer, width()/draft, height()/draft, QImage::Format_RGB32);
QPainter painter(this);
painter.drawImage(QPoint(0, 0), image.scaled(width(), height()));
if(draft>1)
{
draft /= 2;
setWindowTitle(QString("recomputing at 1/%1 resolution...").arg(draft));
update();
}
}
void MandelbrotWidget::mousePressEvent(QMouseEvent *event)
{
if( event->buttons() & Qt::LeftButton )
{
lastpos = event->pos();
double yradius = xradius * height() / width();
center = Eigen::Vector2d(center.x() + (event->pos().x() - width()/2) * xradius * 2 / width(),
center.y() + (event->pos().y() - height()/2) * yradius * 2 / height());
draft = 16;
for(int th = 0; th < threadcount; th++)
threads[th]->terminate();
update();
}
}
void MandelbrotWidget::mouseMoveEvent(QMouseEvent *event)
{
QPoint delta = event->pos() - lastpos;
lastpos = event->pos();
if( event->buttons() & Qt::LeftButton )
{
double t = 1 + 5 * double(delta.y()) / height();
if(t < 0.5) t = 0.5;
if(t > 2) t = 2;
xradius *= t;
draft = 16;
for(int th = 0; th < threadcount; th++)
threads[th]->terminate();
update();
}
}
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
MandelbrotWidget w;
w.show();
return app.exec();
}
#include "mandelbrot.moc"

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