80 lines
1.9 KiB
C
80 lines
1.9 KiB
C
#include <stdlib.h>
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#include <stdint.h>
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#include <unistd.h>
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// Here I use a lcg RNG with a specificaly crafted period to enumerate all pixels
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// and color them by cycling a colormap in a randomish order
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// Same approch as in DOOM (1993)
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// see: Knuth - The Art of Computer Programming, Volume 2: Seminumerical Algorithms
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uint32_t hash32(uint32_t d) {
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// DJB Hash
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uint32_t h = 0x811c9dc5;
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h = (h * 16777619) ^ ((d >> 0) & 0xff);
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h = (h * 16777619) ^ ((d >> 8) & 0xff);
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h = (h * 16777619) ^ ((d >> 16) & 0xff);
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h = (h * 16777619) ^ ((d >> 24) & 0xff);
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return h;
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}
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// must be the next prime after NUM_TOTAL_LEDS
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#define IDLE_PRIME 3203
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// must be a primitive element of the prime residue field |N/IDLE_PRIM
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#define IDLE_PRIM_ELEM 777
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int IDLE_rand(int *seed){
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return *seed = (*seed * IDLE_PRIM_ELEM ) % IDLE_PRIME;
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}
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int IDLE_last_pixel = 34;
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int IDLE_color_offset = 2;
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uint32_t IDLE_colors[5] ={
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0xd31719,
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0x0f6851,
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0xd4772e,
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0xd84b23,
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0x3d89a7
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};
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int Nx, Ny;
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uint8_t *buf;
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void SetPixel(int x, int y, uint8_t r, uint8_t g, uint8_t b){
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buf[3*(x+Nx*y)+0] = r;
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buf[3*(x+Nx*y)+1] = g;
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buf[3*(x+Nx*y)+2] = b;
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}
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void IDLE_set_pixel(){
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int i = IDLE_rand(&IDLE_last_pixel)-1;
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int x = i%Nx;
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int y = i/Nx;
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if (i == IDLE_color_offset){
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IDLE_color_offset++;
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if (IDLE_color_offset > 100)
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IDLE_color_offset=2;
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}
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if (i >= Nx*Ny) return;
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int color_count = sizeof(IDLE_colors)/sizeof(IDLE_colors[0]);
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int color = IDLE_colors[hash32(i+IDLE_color_offset)%color_count];
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SetPixel(x, y, (color>>16)&0xff, (color>>8)&0xff, (color>>0)&0xff);
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}
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int main(int argc, char **argv) {
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Nx = atoi(argv[1]);
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Ny = atoi(argv[2]);
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buf = malloc(Nx*Ny*3);
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int sleepms = atoi(argv[3]);
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if (sleepms == 0) sleepms = 30;
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while(1) {
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IDLE_set_pixel();
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write(1, buf, Nx*Ny*3);
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usleep(1000*sleepms);
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}
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}
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