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Re: Code for collisions
Posted: Sat Feb 07, 2009 5:55 pm
by osgeld
if your using simple shapes physics are the way to go, but in the case of mario up there it becomes much easier to mask it rather than plotting out all those points to a body
Re: Code for collisions
Posted: Sun Feb 08, 2009 12:25 am
by osgeld
ok i didnt comprehend how much crap i had to do today heh
but heres a basic pbm image format reader, i dont really like a couple of things but ill fix that in masklib
issues
1) you have to manually set the image width, cause i didnt snag it out of the header info
2) it really only can deal with 1 image at a time, but this is more about showing how and not a final product
3) its slow, mainly because of the repeat loop
Code: Select all
-- simple binary pbm reader
-- 2007 - 2009 osgeld
-- ( osgeld@cheesefactory.us )
-- CC share alike
-- use, distrubute, remix ect
-- give credit, share updates
data = love.filesystem.read("mario.pbm")
image_width = 439
mask = {}
-- strip the pbm header
for i = 1, 3 do
found = string.find(data, "\n")
data = string.sub(data, found + 1, -1)
end
-- convert from binary to table
local x = 0
local y = 0
for counter = 1, #data do
byte = string.byte(string.sub(data, counter, counter))
byte_value = 128
repeat
if (byte / byte_value) >= 1 then
byte = byte - byte_value
else
table.insert(mask, {x, y})
end
if x < image_width then
x = x + 1
else
x = 0
y = y + 1
end
byte_value = byte_value / 2
until(byte_value < 1)
end
again its not the final product, but i hope it gives you a start
Re: Code for collisions
Posted: Sun Feb 08, 2009 1:58 am
by Skofo
Oh man, pixel-perfect collision. While that looks really neat and I love the effort you put into it, wouldn't it be a lot more efficient most of the time to use vectors, even for complex things like spaceships?
Re: Code for collisions
Posted: Sun Feb 08, 2009 4:13 am
by osgeld
once the lib is done is a matter of 3 mouse clicks in the gimp to make a collision mask
vs even the asteroids ship is 6 cords to map
also to hammer this point home, you will not be checking pixel perfect every loop
Re: Code for collisions
Posted: Sun Feb 08, 2009 9:00 am
by osuf oboys
osgeld wrote:once the lib is done is a matter of 3 mouse clicks in the gimp to make a collision mask
vs even the asteroids ship is 6 cords to map
also to hammer this point home, you will not be checking pixel perfect every loop
For this solution to work reall well, I would preferably like to see that it is capable of handling scaled sprites as well as computing the normals of the collided surfaces (e.g. intrapolating from the nearby pixels).
Do you have an efficient bit-wise AND function that you use for this library? If not, here's one:
Code: Select all
booleanAndResult = {}
for i=0,255 do
booleanAndResult[i] = {}
for j=0,255 do
booleanAndResult[i][j] = 0
for k=0,7 do
if (i % (2 * 2^k)) >= 2^k and (j % (2 * 2^k)) >= 2^k then
booleanAndResult[i][j] = booleanAndResult[i][j] + 2^k
end
end
end
end
function bool32And(x1, x2)
return booleanAndResult[x1 % 256][x2 % 256] +
256 * booleanAndResult[math.floor(x1 / 256) % 256][math.floor(x2 / 256) % 256] +
65536 * booleanAndResult[math.floor(x1 / 65536) % 256][math.floor(x2 / 65536) % 256] +
16777216 * booleanAndResult[math.floor(x1 / 16777216) % 256][math.floor(x2 / 16777216) % 256]
end
Re: Code for collisions
Posted: Sun Feb 08, 2009 6:34 pm
by osgeld
ill see what i can do, and thanks for the bitwise AND, i have one but its not as smooth as yours
Re: Code for collisions
Posted: Mon Feb 09, 2009 10:38 pm
by counterfactual_jones
Yes, but then you need to use their physics. Which is fine for some games, but hey, mario and every other arcade game don't use them, and if you're going for that kind of feel... Opening up the collision functions would be useful, at least for some simple cases I guess.
Re: Code for collisions
Posted: Wed Feb 11, 2009 4:51 pm
by osuf oboys
osgeld wrote:ill see what i can do, and thanks for the bitwise AND, i have one but its not as smooth as yours
Taking modulus to ensure that the quotient remains an integer makes things considerably faster. And so, the following version is better. Still far from the machine instructions though.
Code: Select all
booleanAndResult = {}
for i=0,255 do
booleanAndResult[i] = {}
for j=0,255 do
booleanAndResult[i][j] = 0
for k=0,7 do
if (i % (2 * 2^k)) >= 2^k and (j % (2 * 2^k)) >= 2^k then
booleanAndResult[i][j] = booleanAndResult[i][j] + 2^k
end
end
end
end
booleanXorResult = {}
for i=0,255 do
booleanXorResult[i] = {}
for j=0,255 do
booleanXorResult[i][j] = 0
for k=0,7 do
if ((i % (2 * 2^k)) >= 2^k and (j % (2 * 2^k)) < 2^k) or
((i % (2 * 2^k)) < 2^k and (j % (2 * 2^k)) >= 2^k)
then
booleanXorResult[i][j] = booleanXorResult[i][j] + 2^k
end
end
end
end
function bnot32(x)
return 4294967295 - x
end
function bnot64(x)
return 18446744073709551615 - x
end
function band32(x1, x2)
local sum = 0
local a1, a2
a1 = x1 % 16777216
a2 = x2 % 16777216
sum = sum + booleanAndResult[(x1 - a1) / 16777216][(x2 - a2) / 16777216]
x1 = a1 % 65536
x2 = a2 % 65536
sum = sum + booleanAndResult[(a1 - x1) / 65536][(a2 - x2) / 65536]
a1 = x1 % 256
a2 = x2 % 256
return sum + booleanAndResult[(x1 - a1) / 256][(x2 - a2) / 256] +
booleanAndResult[a1][a2]
end
function bxor32(x1, x2)
local sum = 0
local a1, a2
a1 = x1 % 16777216
a2 = x2 % 16777216
sum = sum + booleanXorResult[(x1 - a1) / 16777216][(x2 - a2) / 16777216]
x1 = a1 % 65536
x2 = a2 % 65536
sum = sum + booleanXorResult[(a1 - x1) / 65536][(a2 - x2) / 65536]
a1 = x1 % 256
a2 = x2 % 256
return sum + booleanXorResult[(x1 - a1) / 256][(x2 - a2) / 256] +
booleanXorResult[a1][a2]
end
Re: Code for collisions
Posted: Wed Feb 11, 2009 7:51 pm
by bartbes
I want to take the credits for that
Re: Code for collisions
Posted: Thu Feb 12, 2009 1:23 pm
by sroccaserra
About spaceships (as mentionned by Peter Hickman in this thread):
In many "modern" 2D shmups (i.e. post 1994), the hitbox of the spaceship and bullets are rectangles slightly smaller than their respective sprites, allowing them to slightly overlap without exploding.
This prevents the "exploding without touching anything" bug when using rectangles for collisions.
In Radiant Silvergun (a classic masterpiece) for instance, there is a cheat code to see these small rectangles. So you can make an awsome 2D game using only rectangles for collisions.
Note that bosses or big ennemies use several rectangle hitboxes that approximate their shape.
And yes, if you use rectangles I guess you can define corresponding bodies and use the LÖVE physic engine.