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