Player-enemy collision (I'm seriously stumped! : update)

[GungnirDev]

I need to make the enemies collide with the player and (for now) destroy the the player. I may add a health system later. I tried using the same script as I used for the bullet-enemy collision for the enemy-player collision but to no avail. The bullet code I used is under ship.lua. Nothing I've tried works or even changes, the enemies just pass right through. Please help.

Also, I'd like to know how I can spawn more enemies once there are no enemies on the screen.

[flashkot]

why you declare CheckCollision() function within love.update() ?

Move its declaration somether outside love.update(). Better place it before all require comands in main.lua

and watch your code identation! Some times it is hard to tell where your functions ends and where starts next function.

And check your hitboxes. They do not match images you use for player and enemies.

If change all this and put code where it should be, yours CheckCollision() works pretty well and collides player with enemies.

Also delete enemies when wey get out of screen. Then you can check if there is no one to fight (if # enemies = 0 then) and add another foes.

[GungnirDev]

OK, I put the BoundingBox in main.lua like you suggested but it's still not working. I've having a hard time wrapping my head around collision, I can't do much of anything with this function cause I don't know why it works (or doesn't, in my case)

I did try playing with the numbers and that at least makes me somewhat understand exactly what the collision function does, but then I tried changing the width and height of the collision functions to 100s to see if that would work (it didn't). Then I tried changing the v.x's to direct player values and taking out the ipairs function to see if a direct approach would work (it didn't) and, since I thought that maybe it would help if the result was a simpler thing that I had already made happen, I changed the desired "result" to love.event.quit() (because I can do that with the escape function) and that didn't work either.

I'm not lazy...just slow... I'm trying though.

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if CheckCollision(player.x,player.y,100,100,enemy.x,enemy.y,100,100) then
	 love.event.quit()

I'm sure there's a million things wrong with this code.

[flashkot]

Again - watch your code indentation!
I love Python for its strict indentation, very nice option for programming language you learn first.

So, take a look at your ship.lua file. You placed collision detection in lines 72-74. Very likely that your problem is what you think, what this is the end of player.update() function. It looks so by indentation of blocks on lines 64-70 and by end at line 76.

But indentation is wrong. You make a trap for yourself.

end on line 76 just closes for opened on line 43. And this for block is used to process bullets. So, no bullets - no collision detection.

[flashkot]

One more trick i like:

put comment on end for very big blocks. It helps to track where this end belongs to

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function player.update(dt)

    -- ... many many pages of very complex code...
	
end -- function player.update

or

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    for i,v in ipairs(player.shots) do

        -- ... many many pages of very complex code...
	
    end -- bullets processing

[ivan]

OK, I put the BoundingBox in main.lua like you suggested but it's still not working. I've having a hard time wrapping my head around collision, I can't do much of anything with this function cause I don't know why it works (or doesn't, in my case)

It's much simpler than you think.
Imagine two rectangles (r1 and r2):

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              -----------
 -----------  |         |
 |         |  |  (r2)   |
 |  (r1)   |  |         |
 |         |  -----------
 -----------

To figure out if they are overlapping you have to check a couple of simple conditions:
is the RIGHT side of r1 LESS than the LEFT side of r2
OR
is the LEFT side of r1 GREATER than the RIGHT side of r2
If any of these two conditions is TRUE the two boxes are NOT intersecting.
That's all there is to it! ...well almost, we have to check the Y axis as well, but it's the same principle.
To put in pseudo code:

Code: Select all

if r1.RIGHT < r2.LEFT or r1.LEFT > r2.RIGHT then
  return false -- no collision
end
if r1.BOTTOM < r2.TOP or r1.TOP > r2.BOTTOM then
  return false -- no collision
end
return true -- in any other case they must be intersecting

Most of the confusion is caused by the different types of bounding box representations.
If I remember correctly BoundingBox.lua accepts an X and Y position for the TOP-LEFT corner of each rectangle along with their WIDTH/HEIGHT.
You could easily write your own version that accept LEFT, TOP, RIGHT, BOTTOM coords for each rectangle.

[ivan]

OK, I put the BoundingBox in main.lua like you suggested but it's still not working. I've having a hard time wrapping my head around collision, I can't do much of anything with this function cause I don't know why it works (or doesn't, in my case)

It's much simpler than you think.
Imagine two rectangles (r1 and r2):

Code: Select all

              -----------
 -----------  |         |
 |         |  |  (r2)   |
 |  (r1)   |  |         |
 |         |  -----------
 -----------

To figure out if they are overlapping you have to check a couple of simple conditions:
is the RIGHT side of r1 LESS than the LEFT side of r2
OR
is the LEFT side of r1 GREATER than the RIGHT side of r2
If any of these two conditions is TRUE the two boxes are NOT intersecting.
That's all there is to it! ...well almost, we have to check the Y axis as well, but it's the same principle.
To put in pseudo code:

Code: Select all

if r1.RIGHT < r2.LEFT or r1.LEFT > r2.RIGHT then
  return false -- no collision
end
if r1.BOTTOM < r2.TOP or r1.TOP > r2.BOTTOM then
  return false -- no collision
end
return true -- in any other case they must be intersecting

Most of the confusion is caused by the different types of bounding box representations.
If I remember correctly BoundingBox.lua accepts an X and Y position for the TOP-LEFT corner of each rectangle along with their WIDTH/HEIGHT.
You could easily write your own version that accept LEFT, TOP, RIGHT, BOTTOM coords for each rectangle.

[Santos]

You might find this helpful to understand rectangle intersection: http://silentmatt.com/rectangle-intersection/
Try moving the rectangles around and see what happens!

Consider having a debugging mode which, when on, draws rectangles around hitboxes and maybe displays other information. To do this, set up a boolean variable in love.load...

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function love.load()

	debugging = true 

You can then draw helpful things if debugging is true...

ship.lua

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function player.draw()

	love.graphics.setColor(255,230,255)

	love.graphics.draw(fighter, player.x, player.y)

	if debugging then
		love.graphics.rectangle('line', player.x, player.y, player.width, player.height)
	end

end

foe.lua

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function foe.draw()

	love.graphics.setColor(255,255,255,255)

	for i,v in ipairs(enemies) do
		love.graphics.draw (wolv, v.x, v.y)

		if debugging then
			love.graphics.rectangle('line', v.x, v.y, v.width, v.height)
		end
	end

end

To quit the game when the player touches an enemy, try this:

• Loop through all the enemies
• Check for collisions between the player and the current enemy in the loop

You can do this by putting this right at the start of player.update:

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for _, enemy in ipairs(enemies) do
	if CheckCollision(player.x, player.y, player.width, player.height, enemy.x, enemy.y, enemy.width, enemy.height) then
		love.event.quit()
	end
end

[GungnirDev]

Ok Santos, your code worked which is pretty much just how I thought it would. I think the problem wasn't me not getting collision but rather me not looping through the right objects. Good concept, bad coding, I think. But thanks!

IDK about the respawning enemies though. I tried putting the update function in foe.update but the enemies won't spawn.

I figured that the problem might be that not all the enemies are getting removed, but I have the mark and remove function in both foe.update and ship.update so it should remove the enemies, right?

I cleaned up the code a little, and also I made music! In GarageBand. It's kinda fail but it's original and it plays OK. At least sound is easy to do in love...

[Santos]

I like the music!

First of all, it would be really useful to know how many enemies there are, that way you can see if they are being removed or not:

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function foe.draw()
	love.graphics.print('#enemies: '..#enemies, 10, 10)

Hmm, it seems like they're not. Next step: checking the code which removes enemies!

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-- mark enemies that are not visible for removal
if v.y < 0 then
	table.insert(remEnemy, i)
end

In LÖVE, a y coordinate of 0 is the top of the screen, so this is actually checking if the enemy is above the screen! Let's fix this:

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-- mark enemies that are not visible for removal
if v.y > love.graphics.getHeight() then
	table.insert(remEnemy, i)
end

Now we can see from the number of enemies that they are actually being removed. But no new enemies are being created...

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if # enemies == 0 then
	for i=0,4 do
		enemy = {}
		enemy.width = 40
		enemy.height = 20
		enemy.x = i * (enemy.width + 100) + 100
		enemy.y = i * (enemy.height + 50) + 100
	end
end

The enemy table is being made... but it's not being inserted into the enemies table.

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if # enemies == 0 then
	for i=0,4 do
		enemy = {}
		enemy.width = 40
		enemy.height = 20
		enemy.x = i * (enemy.width + 100) + 100
		enemy.y = i * (enemy.height + 50) + 100
		table.insert(enemies, enemy)
	end
end

And it works!