borgware-2d/animations/blackhole.c

91 lines
2.6 KiB
C

#include <stdint.h>
#include "../config.h"
#include "../pixel.h"
#include "../util.h"
#include "../compat/pgmspace.h"
#include "blackhole.h"
// macro for simplifying flash memory access
#define PGM(x) pgm_read_byte(&(x))
/**
* Integer variant of the sine function which takes an integer based angle
* (range from 0 to 63) where sin_i(64) corresponds to sin(2 * M_PI) * 64 and
* sin_i(16) corresponds to sin(M_PI_2) * 64 (each excluding the fractional
* part). It uses a lookup table which models one quarter of a full sine period
* and calculates the rest of the function from that quarter.
* @param angle angle based on an integer (range from 0 to 63)
* @return result of the sine function normalized to a range from -64 to 64
*/
static signed char sin_i(signed char angle) {
// the aforementioned lookup table
static signed char const sine_table[] PROGMEM =
{0, 6, 12, 19, 24, 30, 36, 41, 45, 49, 53, 56, 59, 61, 63, 64};
// determine correct index for the lookup table depending on the given angle
angle %= 64u;
unsigned char index;
if (angle < 16) {
index = angle;
} else if (angle < 32) {
index = 31 - angle;
} else if (angle < 48) {
index = angle - 32;
} else {
index = 63 - angle;
}
return (signed char)(PGM(sine_table[index])) * (angle < 32 ? 1 : -1);
}
/**
* Integer variant of the cosine function which takes an integer based angle
* (range from 0 to 63) where cos_i(64) corresponds to cos(2 * M_PI) * 64 and
* cos_i(16) corresponds to cos(M_PI_2) * 64. It uses the sin_i function and
* shifts the given angle by 16 (which corresponds to a delta of 90 degrees).
* @param angle angle based on an integer (range from 0 to 63)
* @return result of the cosine function normalized to a range from -64 to 64
*/
static signed char cos_i(unsigned char const angle) {
return sin_i(angle + 16);
}
#define NUM_CIRCLE 7
/**
* Draws a black hole like pattern (viewed from different perspectives).
*/
void blackhole(void) {
signed char firstRadius = 80, helpRadius, angle = 0, add = 0;
// initialize data
for (unsigned int k = 0; k < 800; k++) {
if (k > 300) {
add = k / 16;
}
helpRadius = firstRadius;
for (signed char i = 0; i < NUM_CIRCLE; i++) {
for (signed char j = 0; j < 64; j += 8) {
signed char a = (j & 0x08) ? 0 : 4;
pixel p;
p.x = (64 + cos_i(angle + j + a) * helpRadius / 64) >> 3;
p.y = (64 + sin_i(angle + add + j + a) * helpRadius / 64) >> 3;
if ((p.x < NUM_COLS) && (p.y < NUM_ROWS)) {
setpixel(p, 3);
}
}
helpRadius = (helpRadius * 2) / 3;
}
wait(30);
clear_screen(0);
angle++;
firstRadius += 2;
if (firstRadius > 119) {
firstRadius = 80;
}
}
}