C++ Allegro 5 Made Easy Tutorial 17 - Sprite Transparency Video Lecture | Allegro: A Complete Guide - Game Development

hello everybody and welcome to your next
Allegro fire tutorial so in this
tutorial we're going to be learning
about spray transparency so in the last
tutorial we loaded in our maps our
sprites and stuff like that but as you
notice that I had the background color
and there because I they were in a JPEG
format and the problem with jpg or
bitmaps or like BMPs or anything like
that
is that um they they don't have an alpha
channel which means that they cannot be
transparent so for allegra for users and
stuff the default color for color mask
or for alpha channel or in those type of
file formats would be would be the color
magenta which is 255 red 0 green and 255
blue and the RGB color scale but with
allegra 5 they allow you to specify
which type of color you want a mask or
which color you wanna add an alpha
channel to so let me erase kind of this
stuff in the last tutorial
but what we're gonna do is that I'm
gonna be I created an image right here
and as you can see it's just a black box
and with a little blue box inside and
the black box is what I'm gonna be I'll
create I'm making transparent so I'm
gonna turn that I'm gonna when we draw
it to a screen we're not gonna see the
black box around it we're only going to
see the blue box inside of it okay so
you get to a code once we get to our
loading and what we do is I'm loading in
an image and my image just called tests
are BMP I will the function that we're
focusing on now is al underscore convert
underscore color
I mean underscore not underscore to
underscore out for we put in the image
we want to mask and then we put in the
color that we want to mask so we put in
the clothes that we just don't want to
see okay so in this case I'm going to
said I'm putting the image in there and
I'm sending the color mask equal to zero
zero zero four black okay so and
therefore we're not gonna be able to see
black everything in the code relative
you should really understand and the
drunk man I just draw it regularly so I
drop the image I want to once I draw the
image you shouldn't see the black
background and I said clear the color to
white soldiers you can see that's just
not blending in with the background so
you can actually see that we're not
actually seeing the the black background
of the image so that's how you handle
transparency without your sprites so one
last thing I want to leave you will
leave with you before this tutorial is
done is that notice like one thing just
to pay attention to is that since we
draw when we crop this image over here
right here remember that this the whole
image is like the origin position is
still at the top left of the image so
even though we still can't see the black
area it's kind of as though like we're
calculating the area of this right so
this would represent X and y and this
corner represent X and y x and y - even
though we're only only even though we're
only seeing this part of the image it's
drawing it like the whole image but it's
mask in this color so we can't see it so
this is relatively important when we get
into collision and I'll expand more
about it when we get in collision but in
scenarios like this most likely you want
to use pixel collision rather than
bounding box collision and lastly most
of the time you're going to want to use
a PNG image if you want to have
transparency in your images then I
highly recommend that you just use a PNG
image with transparency
now the reason being is that um
sometimes you want more sometimes you
want more than one cause to be
transparent and you could probably do
that with a level 5 as well but the
problem is that say you will say you
have like three different transparent
colors in your image right but you don't
want them to clash or other images and
you don't want it to erase certain
images because the color mask you go run
into some problem
so if you really want transparency in
your images and I really recommend use
PNG so you can set exactly what you want
transparent and what you don't want to
be transparent and what you see is what
you get in your program
so anyways this is that for this
tutorial hope you enjoyed it thanks for
watching and bye