Drawing circles outside the screen

[mwclarkson]

OK, I'm still pretty new with Arduino/C although I've done a fair bit of simple VB/C++/Python/Java.

I'm still playing with circles from the tutorial in the book and I'm trying to get a crawling line of pixels marching across the screen.

I can get them to move off the right edge before jumping back to the left but they won't reappear on the left until the centre of the circle has reached x:0 (so the entire right side of the circle pops in at once).

If I make the circles march the other way they appear neatly on the right but pop out poorly on the left (again, once the centre his x:0).

Is this a hardware limitation or have I done something obviously dumb with my programming?


#include <EEPROM.h>
#include <SPI.h>
#include <GD2.h>

int num; // Number of dots
int r; // Radius of dots
int spacing; // Space allowed for each dot
int dot[10]; // Position of each dot

void setup()
{
 num = 12;
 r = 15;
 spacing = 480/(num-2); // This should give a zone of 48 px per cirlce
                        // for 10 circles in a row
 for (int i = 0;i<num;i++)
 {
   dot[i] = spacing*(i-1); // Should start .|..........|.
                           // Where | is the edge of the screen
 }
 GD.begin();
}

void loop()
{
 
 GD.ClearColorRGB(0x000000);
 GD.Clear();
 
 GD.PointSize(16*r);
 GD.Begin(POINTS);
 for (int i = 0; i <num; i++)
 {
   GD.Vertex2ii(dot[i],100);
   GD.Vertex2ii(480-dot[i],170);
   dot[i]++;
   if(dot[i] > (480+spacing)) { dot[i] = - spacing; }
 }

 GD.swap();
 delay(5);
}

[jamesbowman]

Aha, this is a bit subtle .. the problem is that Vertex2ii can only handle positive coordinates.

The book talks about this on p.55, and covers Vertex2f() - which can handle negative coordinates. excamera.com/files/gd2book_v0.pdf

So changing the code (I also corrected the size of the "dot[]" array):


#include <EEPROM.h>
#include <SPI.h>
#include <GD2.h>

int num; // Number of dots
int r; // Radius of dots
int spacing; // Space allowed for each dot
int dot[12]; // Position of each dot

void setup()
{
 num = 12;
 r = 15;
 spacing = 480/(num-2); // This should give a zone of 48 px per cirlce
                        // for 10 circles in a row
 for (int i = 0;i<num;i++)
 {
   dot[i] = spacing*(i-1); // Should start .|..........|.
                           // Where | is the edge of the screen
 }
 GD.begin();
}

void loop()
{

 GD.ClearColorRGB(0x000000);
 GD.Clear();

 GD.PointSize(16*r);
 GD.Begin(POINTS);
 for (int i = 0; i <num; i++)
 {
   GD.Vertex2f(16 * dot[i], 16 * 100);
   GD.Vertex2f(16 * (480-dot[i]), 16 * 170);
   dot[i]++;
 }

 GD.swap();
 delay(5);
}
Gives this:

[mwclarkson]

Thank you very much!

So I had done something dumb with my programming (array declaration), but that wasn't my only problem. :-)

I had a skim read through the book before I started, but reading without doing I have inevitably missed an awful lot.

Have to say, I'm really impressed so far. Once I get a bit more comfortable trouble shooting I'm looking forward to throwing these at my students (11-18) to see what they come up with.