Colors in the MacroLibX

Colors in the MacroLibX are presented in an int format just like the minilibx. It therefore requires some tricky things in order to obtain an int which can contain the ARGB values.

One improvement over minilibx is that MacroLibX fully supports transparency, whether in pixel put, images or string put.

🌈 The color integer standard

As mentioned above, MacroLibX uses an ARGB color format, which in int is equivalent to 0xAARRGGBB. This ARGB is composed by 4 values :

• A, the alpha of the color (it’s transparency), between 0 and 255
• R, the red component, between 0 and 255
• G, the green component, between 0 and 255
• B, the blue component, between 0 and 255

You can directly encode colors using hexadecimal in C/C++ like so :

int main(void)
{
    /* Do stuffs */

    mlx_pixel_put(mlx, win, 10, 10, 0xFF223344);

    /* Do stuffs */
}

But sometime we cannot use the usefull hexadecimal to encode colors…

🔐 Encode and decode colors

We can use two methods to encode and decode colors:

• bit-shifting
• char / int conversion

Bit-shifting

Since each byte contains 2^8 = 256 values (1 byte = 8 bits), and ARGB values range from 0 to 255, we can perfectly fit a integer (as an int is 4 bytes, on 64bits systems…).

In order to set the values programatically we can use bit-shifting. Let’s create a function which does precisely that for us :

int create_argb(int a, int r, int g, int b)
{
    return (a << 24 | r << 16 | g << 8 | b);
}

Because ints are stored from right to left, we need to bit-shift each value the according amount of bits backwards. We can also do the exact opposite and retrieve integer values from an encoded ARGB integer :

int get_a(int argb)
{
    return ((argb >> 24) & 0xFF);
}

int get_r(int argb)
{
    return ((argb >> 16) & 0xFF);
}

int get_g(int argb)
{
    return ((argb >> 8) & 0xFF);
}

int get_b(int argb)
{
    return (argb & 0xFF);
}

char / int conversion

As mentioned above ARGB contains 4 bytes, and 4 bytes can be seen as 4 unsigned char. We can therefore use 4 unsigned char to extract and insert ARGB components into our colors :

int create_argb(unsigned char a, unsigned char r, unsigned char g, unsigned char b)
{
    unsigned char bits[4] = {b, g, r , a};
    return *((int*)bits);
}

unsigned char get_a(int argb)
{
    unsigned char* bits = &argb;
    return bits[3];
}

unsigned char get_r(int argb)
{
    unsigned char* bits = &argb;
    return bits[2];
}

unsigned char get_g(int argb)
{
    unsigned char* bits = &argb;
    return bits[1];
}

unsigned char get_b(int argb)
{
    unsigned char* bits = &argb;
    return bits[0];
}