joystick quantization visualization

joymap.c

#if 0
gcc -std=c99 -Wall -Wextra -pedantic -g -O4 -march=native $0 -lm || exit 1
./a.out && feh joymap.ppm
exit $?
#endif

// visualization of analog joystick to 8-way digital direction quantization
// see https://github.com/sulix/omnispeak/pull/14

#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>


#define NEW_QUANTIZER 1

#define DEADZONE_PERCENT 30
//#define DIAG_SLOPE  29,70
#define DIAG_SLOPE  1,3

#define OUTPUT_SIZE 256


uint8_t img[OUTPUT_SIZE * OUTPUT_SIZE * 3];
int deadzone, slopeA, slopeB;

uint32_t colors[9] = {
    0x00E0FF, 0x00FF80, 0x80FF00,
    0x0000FF, 0x000000, 0xFFFF00,
    0x8000FF, 0xFF0080, 0xFF0000,
};


#if NEW_QUANTIZER

void process(int inX, int inY, int *outX, int *outY) {
    if ((inX * inX + inY * inY) < deadzone) {
        *outX = *outY = 0;
        return;
    }
    int signX = inX >> 31;
    int signY = inY >> 31;
    inX = abs(inX);
    inY = abs(inY);
    int resX = (inY * slopeA > inX * slopeB) ? 0 : 32767;
    int resY = (inX * slopeA > inY * slopeB) ? 0 : 32767;
    if (resX & resY) { resX = resY = 23168; }
    *outX = (resX ^ signX) - signX;
    *outY = (resY ^ signY) - signY;
}

#else

void process(int inX, int inY, int *outX, int *outY) {
    *outX = ((inX * inX) < deadzone) ? 0 : inX;
    *outY = ((inY * inY) < deadzone) ? 0 : inY;
}

#endif


int main(void) {
    const int _s[2] = { DIAG_SLOPE };
    deadzone = DEADZONE_PERCENT * 32767 / 100;
    deadzone *= deadzone;
    slopeA = _s[0];
    slopeB = _s[1];

    uint8_t* p = img;
    for (int iy = 0;  iy < OUTPUT_SIZE;  ++iy) {
        for (int ix = 0;  ix < OUTPUT_SIZE;  ++ix) {
            int x = ((ix * 65536 + 32767 + OUTPUT_SIZE/2) / OUTPUT_SIZE) - 32768;
            int y = ((iy * 65536 + 32767 + OUTPUT_SIZE/2) / OUTPUT_SIZE) - 32768;
            bool out = (x*x + y*y) > 0x40000000;
            process(x, y, &x, &y);
            x = (x < 0) ? 0 : (x > 0) ? 2 : 1;
            y = (y < 0) ? 0 : (y > 0) ? 2 : 1;
            uint32_t color = colors[y * 3 + x];
            if (out) { color = (color >> 2) & 0x3F3F3F; }
            if (ix == (OUTPUT_SIZE / 2)) { color = ~((~color >> 1) & 0x7F7F7F); }
            if (iy == (OUTPUT_SIZE / 2)) { color = ~((~color >> 1) & 0x7F7F7F); }
            *p++ = (uint8_t) (color >> 16);
            *p++ = (uint8_t) (color >>  8);
            *p++ = (uint8_t)  color;
        }
    }

    FILE *f = fopen("joymap.ppm", "wb");
    fprintf(f, "P6\n%d %d\n255\n", OUTPUT_SIZE, OUTPUT_SIZE);
    fwrite(img, OUTPUT_SIZE, OUTPUT_SIZE * 3, f);
    fclose(f);

    return 0;
}