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113 lines
2.6 KiB
Arduino

5 years ago
/*
* good old starfield - PASTIS 51 EDITION
*
* See starfield25 for context and more comments, otherwise it may not make much
* sense...
*
* So basically the trick used to get more stars here, is not to free memory,
* because that's not possible, but instead it's to make the stars use less memory.
* To do that we change the type from float (4 bytes) to int (2 bytes).
* The tradeoff is of course that now we have integers and not floating point numbers,
* and that prevents us to have any meaningful results when we calculate vector related
* stuff. But there's a workaround to this!
* The workaround is very simple, we use int as floats without floating points, which
* means that everytime we read from the array we convert the int to float and divide
* it by an arbitrary precision value (here we use 100), and when we want to store a
* float we multiply it by the same precision value and convert to int.
* We loose in accuray, but that does not matter here at all.
*
* ex: we want to store 12,345678
* 12,3456 * 100 = 1234,56
* int(1234,56) = 1234
* and converted back
* float(1234 / 100) = 12,34
* in the process with this trick we lost 0,005678 (who cares?)
*
* Note: most of the changes are in new_star(). There are some minor changes elsewhere,
* mostly to try optimise things cheaply, ignore.
*/
#include <TVout.h>
TVout TV;
#define STARS 51
int x[STARS];
int y[STARS];
int vx[STARS];
int vy[STARS];
void
setup()
{
randomSeed(analogRead(6)); // effective?
TV.begin(NTSC,120,96);
new_stars();
}
void
new_star(uint8_t i)
{
uint8_t x_tmp, y_tmp;
uint8_t ox = 60;
uint8_t oy = 48;
int dx, dy;
float vl;
x_tmp = 30 + random(60);
y_tmp = 24 + random(48);
dx = x_tmp - ox;
dy = y_tmp - oy;
switch(dx)
case 0: dx = 1; // CHEAT
vl = 1 / sqrt(dx*dx + dy*dy);
vx[i] = int(dx * vl * 100);
vy[i] = int(dy * vl * 100);
x[i] = x_tmp * 100;
y[i] = y_tmp * 100;
}
void
new_stars()
{
for (uint8_t i = 0; i < STARS; i++)
new_star(i);
}
void
update_stars()
{
for (uint8_t i = 0; i < 40; i++) {
x[i] = x[i] + vx[i];
y[i] = y[i] + vy[i];
if (x[i] > 12000 || x[i] < 0 || y[i] < 0 || y[i] > 9600)
new_star(i);
}
for (uint8_t i = 40; i < STARS; i++) {
x[i] = x[i] + (vx[i] << 1);
y[i] = y[i] + (vy[i] << 1);
if (x[i] > 12000 || x[i] < 0 || y[i] < 0 || y[i] > 9600)
new_star(i);
}
}
void
draw_stars()
{
for (uint8_t i = 0; i < STARS; i++)
TV.set_pixel(x[i]/100, y[i]/100, 1);
}
void
loop()
{
TV.delay_frame(1);
update_stars();
TV.clear_screen();
draw_stars();
}