[B]Segmentation Fault Code 139?[/B]

[vivichrist]

I think I maybe doing recursion wrong...?

main.cc

#include "myarea.h"
#include <gtkmm/main.h>
#include <gtkmm/window.h>

int main(int argc, char** argv)
{
Gtk::Main kit(argc, argv);

Gtk::Window win;
win.set_title("DrawingArea");

MyArea area;
win.add(area);
area.show();

Gtk::Main::run(win);

return 0;
}

myarea.h

#ifndef GTKMM_EXAMPLE_MYAREA_H
#define GTKMM_EXAMPLE_MYAREA_H

#include <vector>
#include <gtkmm/drawingarea.h>
#include "linesegment.h"

class MyArea : public Gtk::DrawingArea
{
double sx, sy, length;
double branchAngle;
double shrinkage;
int numBranches;
std::vector<LineSegment> lines;
public:
MyArea();
virtual ~MyArea();

protected:
//Override default signal handler:
void make_tree(double nx, double ny, double dist, double ang, int branches, double propor);
virtual bool on_expose_event(GdkEventExpose* event);
};

#endif // GTKMM_EXAMPLE_MYAREA_H

myarea.cc

#include "myarea.h"
#include <cmath>
#include <stdlib.h>
#include <cairomm/context.h>

using namespace std;

MyArea::MyArea(){
branchAngle = M_PI*0.3333333333*(0.1+rand()*0.000012207);
shrinkage = 0.5 + rand()*0.0000030518;
numBranches = 5+rand()*0.000091553;
sx = (double)(rand()%900);
sy = (double)(400.0 + rand()%100);
length = (double)(50 +(rand()%150));
LineSegment line(sx, sy, sx, sy-length);
lines.push_back(line);
make_tree(sx, sy, length, -M_PI*0.5, 2, 1.0);
}

MyArea::~MyArea()
{
}

bool MyArea::on_expose_event(GdkEventExpose* event)
{
// This is where we draw on the window
Glib::RefPtr<Gdk::Window> window = get_window();
if(window)
{
Gtk::Allocation allocation = get_allocation();
const int width = allocation.get_width();
const int height = allocation.get_height();

// generate a tree coordinates from random center of the window


Cairo::RefPtr<Cairo::Context> cr = window->create_cairo_context();


// clip to the area indicated by the expose event so that we only redraw
// the portion of the window that needs to be redrawn
cr->rectangle(event->area.x, event->area.y,
event->area.width, event->area.height);
cr->clip();

// draw red lines out from the center of the window
cr->set_source_rgb(0.8, 0.0, 0.0);
for(int i=0;i<(int)lines.size();i++){
cr->set_line_width(sqrt((lines[i].fx-lines[i].fy)+(lines[i].tx-lines[i].ty))*0.05);
cr->move_to(lines[i].fx, lines[i].fy);
cr->line_to(lines[i].tx, lines[i].ty);
cr->stroke();
}
}

return true;
}

void MyArea::make_tree(double nx, double ny, double dist, double ang, int branches, double propor){
// double rnddist = dist*((1-branches*0.1)*rand()+(branches*0.1));
double newx = nx + dist*cos(ang);
double newy = ny + dist*sin(ang);

int cap = fmin(branches, numBranches);
if (dist>3+(5.0/length))
for (int i=1;i<=cap;i++)
make_tree(newx, newy, dist*shrinkage, ang-(branchAngle*propor*i*(i%2>0?-1:1)), branches+1, propor);
};

[lloyd_b]

I'm not sure "shrinkage" is in fact shrinkage - rand() returns a value between 1 and MAX_INT (which on most machines is 4,294,967,296). With this calculation
shrinkage = 0.5 + rand()*0.0000030518; for shrinkage, you end up with maximum value for shrinkage of 13107.88. Which would be more "growage" than "shrinkage".

If shrinkage is greater than 1, then if this test
if (dist>3+(5.0/length)) is true to start with, then you've got endless recursion, as "length" doesn't change, and "dist" will increase each time you recurse.

I'm guessing you're working from example code that presumes MAX_INT to be 65536 (16 bit int's) rather than 4,294,967,296 (32 bit int's), in which case
shrinkage = 0.5 + (rand()%65536)*0.0000030518; should ensure shrinkage is never greater than 1 (it would have a max value of 0.7).

Lloyd B.

[vivichrist]

thanks so much lloyd_b that was a really insane problem that was driving me round the bend. I still have the problem of having nothing rendered... perhaps I should have made a const for 1/MAX_INT ? but yeah cheers and kudos to you! :D

[vivichrist]

so, working code goes something like this:


#include "myarea.h"
#include <limits>
#include <cmath>
#include <stdlib.h>
#include <cairomm/context.h>

using namespace std;

MyArea::MyArea()
{
const double inverter = 1/std::numeric_limits<int>::max();
branchAngle = M_PI*0.3333333333*(0.1+rand()*inverter*0.5);
shrinkage = 0.5+rand()*inverter*0.1;
numBranches = 5+rand()*inverter*3;
sx = (double)(rand()%900);
sy = (double)(400.0 + rand()%100);
length = (double)(50 +(rand()%150));
LineSegment line(sx, sy, sx, sy-length);
lines.push_back(line);
make_tree(sx, sy, length, -M_PI*0.5, 2, 1.0);
}

MyArea::~MyArea()
{
}

bool MyArea::on_expose_event(GdkEventExpose* event)
{
// This is where we draw on the window
Glib::RefPtr<Gdk::Window> window = get_window();
if(window)
{
Gtk::Allocation allocation = get_allocation();
const int width = allocation.get_width();
const int height = allocation.get_height();
cout << "drawing" << endl;

// generate a tree coordinates from random center of the window


Cairo::RefPtr<Cairo::Context> cr = window->create_cairo_context();


// clip to the area indicated by the expose event so that we only redraw
// the portion of the window that needs to be redrawn
cr->rectangle(event->area.x, event->area.y,
event->area.width, event->area.height);
cr->clip();

// draw red lines out from the center of the window
cr->set_source_rgb(0.8, 0.0, 0.0);
for(int i=0;i<(int)lines.size();i++){
cr->set_line_width(sqrt(abs(lines[i].fx-lines[i].fy)+abs(lines[i].tx-lines[i].ty))*0.1);
// cout << "linewidth:" << sqrt(abs(lines[i].fx-lines[i].fy)+abs(lines[i].tx-lines[i].ty))*0.5 << endl;
cr->move_to(lines[i].fx, lines[i].fy);
// cout << "move:" << lines[i].fx << ":" << lines[i].fy << endl;
cr->line_to(lines[i].tx, lines[i].ty);
// cout << "line:" << lines[i].tx << ":" << lines[i].ty << endl;
cr->stroke();
}
}

return true;
}

void MyArea::make_tree(double nx, double ny, double dist, double ang, int branches, double propor){
// double rnddist = dist*((1-branches*0.1)*rand()+(branches*0.1));
double newx = nx + dist*cos(ang);
double newy = ny + dist*sin(ang);
LineSegment line(nx, ny, newx, newy);
lines.push_back(line);
int cap = fmin(branches, numBranches);
if (dist>3) //+(5.0/length)
for (int i=1;i<=cap;i++)
make_tree(newx, newy, dist*shrinkage, ang-(branchAngle*propor*i*(i%2>0?-1:1)), branches+1, propor);
};