matrix.c

static void
m3_unity(f32 result[static 9])
{
    memset(result, 0x00, 9 * sizeof(f32));
    
    result[0] = result[4] = result[8] = 1.0f;
}

static void
m3_mul(f32 result[static 9], f32 A[static 9], f32 B[static 9])
{
    result[0] = A[0] * B[0] + A[1] * B[3] + A[2] * B[6];
    result[1] = A[0] * B[1] + A[1] * B[4] + A[2] * B[7];
    result[2] = A[0] * B[2] + A[1] * B[5] + A[2] * B[8];
    
    result[3] = A[3] * B[0] + A[4] * B[3] + A[5] * B[6];
    result[4] = A[3] * B[1] + A[4] * B[4] + A[5] * B[7];
    result[5] = A[3] * B[2] + A[4] * B[5] + A[5] * B[8];
    
    result[6] = A[6] * B[0] + A[7] * B[3] + A[8] * B[6];
    result[7] = A[6] * B[1] + A[7] * B[4] + A[8] * B[7];
    result[8] = A[6] * B[2] + A[7] * B[5] + A[8] * B[8];
}

static v3
m3_apply(f32 A[static 9], v3 vec)
{
    v3 result;
    
    result.x = A[0] * vec.x + A[1] * vec.y + A[2] * vec.w;
    result.y = A[3] * vec.x + A[4] * vec.y + A[5] * vec.w;
    result.w = A[6] * vec.x + A[7] * vec.y + A[8] * vec.w;
    
    return(result);
}

static void
m3_scale(f32 result[static 9], v2 factor)
{
    m3_unity(result);
    
    result[0] = factor.x;
    result[4] = factor.y;
}

static void
m3_translate(f32 result[static 9], v2 dir)
{
    m3_unity(result);
    
    result[2] = dir.x;
    result[5] = dir.y;
}

static void
m3_rotate(f32 result[static 9], v2 center, f32 rad)
{
    v2 center_back;
    center_back.x = -1.0f * center.x;
    center_back.y = -1.0f * center.y;
    
    f32 translate_and_rotate[9];
    f32 translate[9];
    f32 translate_back[9];
    f32 rotate[9];
    
    m3_translate(translate, center);
    m3_translate(translate_back, center_back);
    m3_unity(rotate);
    
    rotate[0] = cosf(rad);
    rotate[1] = sinf(rad);
    rotate[3] = -1.0f * sinf(rad);
    rotate[4] = cosf(rad);
    
    m3_mul(translate_and_rotate, translate, rotate);
    m3_mul(result, translate_and_rotate, translate_back);
}