load_obj

function [V, F] = load_obj(filename)
    # read obj
    # input:
    #   filename - obj file path
    # output:
    #   V - vertex matrix [N, 3]
    #   F - face matrix [M, 3]

    fid = fopen(filename, "r");

    init_capacity = 10000;

    V = zeros(init_capacity, 3);
    F = zeros(init_capacity, 3);

    v_count = 0;
    f_count = 0;

    while ~feof(fid)
        line = strtrim(fgetl(fid));
        if startsWith(line, "v ")
            vals = sscanf(line(3:end), "%f %f %f");  # [3, 1]
            v_count += 1;
            if v_count > size(V, 1)
                V = [V; zeros(size(V))];  # double capacity
            end
            V(v_count, :) = transpose(vals);
            if mod(v_count, 10000) == 0
                printf("Loaded %d vertices\n", v_count);
            end
        elseif startsWith(line, "f ")
            idx = sscanf(line(3:end), "%d %d %d");  # [3, 1]
            f_count += 1;
            if f_count > size(F, 1)
                F = [F; zeros(size(F))];  # double capacity
            end
            F(f_count, :) = transpose(idx);
            if mod(f_count, 10000) == 0
                printf("Loaded %d faces\n", f_count);
            end
        end
    end
    fclose(fid);

    # trim to actual size
    V = V(1:v_count, :);
    F = F(1:f_count, :);

end