Ply file colors to spherical

colors_to_spherical.c

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

float toSH(uint8_t b) {
    double C0 = 0.28209479177387814;
    return ((b / 255.0) - 0.5) / C0;
}

void convert_and_write(FILE *input, FILE *output) {
    uint8_t buffer[373];
    float converted[3];

    fread(buffer, 1, 373, input);
    fwrite(buffer, 1, 59, output);
    fwrite(
        "property float x\n"
        "property float y\n"
        "property float z\n"
        "property float nx\n"
        "property float ny\n"
        "property float nz\n"
        "property float f_dc_0\n"
        "property float f_dc_1\n"
        "property float f_dc_2\n"
        "property float opacity\n"
        "property float scale_0\n"
        "property float scale_1\n"
        "property float scale_2\n"
        "property float rot_0\n"
        "property float rot_1\n"
        "property float rot_2\n"
        "property float rot_3\n"
        "end_header\n", 1, 358, output);

    while (fread(buffer, 1, 59, input) == 59) {
        // Convert the three uint8s at the end of the buffer to floats
        converted[0] = toSH(buffer[24]);
        converted[1] = toSH(buffer[25]);
        converted[2] = toSH(buffer[26]);

        // Write the first 56 bytes unchanged
        fwrite(buffer, 1, 24, output);

        // Write the three floats
        fwrite(converted, sizeof(float), 3, output);

        // Write the rest of the buffer
        fwrite(buffer + 27, 1, 32, output);
    }
}

int main(int argc, char *argv[]) {
    if (argc != 3) {
        fprintf(stderr, "Usage: %s <input file> <output file>\n", argv[0]);
        return 1;
    }

    FILE *input = fopen(argv[1], "rb");
    if (input == NULL) {
        perror("Error opening input file");
        return 1;
    }

    FILE *output = fopen(argv[2], "wb");
    if (output == NULL) {
        perror("Error opening output file");
        fclose(input);
        return 1;
    }

    convert_and_write(input, output);

    fclose(input);
    fclose(output);

    return 0;
}