如何在 Love2d 中使用边界框？
How to use bounding box in Love2d?
我一直在使用一些极其庞大的代码来检测简单对象之间的碰撞，而且我听说过边界框。我找不到任何关于如何使用它的教程，所以我在询问如何使用它。这是我检测碰撞的方法：
function platform.collision()
if player.x + player.width / 2 <= platform.x + platform.width and
player.x + player.width / 2 >= platform.x and
player.y + player.height <= platform.y + platform.height and
player.y + player.height >= platform.y then
MDN has a rather concise article on 2D collision detection。作为 MDN，示例在 javascript 中，但很容易翻译成任何语言并适用于任何语言 - 包括 Lua.
一起来看看：
Axis-Aligned Bounding Box
One of the simpler forms of collision detection is between two rectangles that are axis aligned — meaning no rotation. The algorithm works by ensuring there is no gap between any of the 4 sides of the rectangles. Any gap means a collision does not exist.
他们的例子，翻译成Lua：
local rect1 = { x = 5, y = 5, width = 50, height = 50 }
local rect2 = { x = 20, y = 10, width = 10, height = 10 }
if
rect1.x < rect2.x + rect2.width and
rect1.x + rect1.width > rect2.x and
rect1.y < rect2.y + rect2.height and
rect1.height + rect1.y > rect2.y
then
-- collision detected!
end
-- filling in the values =>
if
5 < 30 and
55 > 20 and
5 < 20 and
55 > 10
then
-- collision detected!
end
A live example，在 JavaScript 中再次证明了这一点。
这是一个快速（但不完美）的 Love2D 示例，您可以将其放入 main.lua 中并进行试验。
local function rect (x, y, w, h, color)
return { x = x, y = y, width = w, height = h, color = color }
end
local function draw_rect (rect)
love.graphics.setColor(unpack(rect.color))
love.graphics.rectangle('fill', rect.x, rect.y,
rect.width, rect.height)
end
local function collides (one, two)
return (
one.x < two.x + two.width and
one.x + one.width > two.x and
one.y < two.y + two.height and
one.y + one.height > two.y
)
end
local kp = love.keyboard.isDown
local red = { 255, 0, 0, 255 }
local green = { 0, 255, 0, 255 }
local blue = { 0, 0, 255, 255 }
local dim1 = rect(5, 5, 50, 50, red)
local dim2 = rect(20, 10, 60, 40, green)
function love.update ()
if kp('up') then
dim2.y = dim2.y - 1
end
if kp('down') then
dim2.y = dim2.y + 1
end
if kp('left') then
dim2.x = dim2.x - 1
end
if kp('right') then
dim2.x = dim2.x + 1
end
dim2.color = collides(dim1, dim2) and green or blue
end
function love.draw ()
draw_rect(dim1)
draw_rect(dim2)
end
Oka 解释得很好。这适用于所有矩形、未旋转和轴对齐的东西。你甚至已经这样做了。这非常适合按钮之类的东西！
但我喜欢做的是在物体周围使用（不可见的）圆圈，看看它们是否发生碰撞。这适用于高度与宽度大致相同的所有内容（许多横向卷轴平台游戏或自上而下的角色扮演游戏就是这种情况）。
如果你想让对象在当前位置居中，这是非常方便的。在触摸屏设备上模拟手指特别有用，因为手指比鼠标光标大很多。 ;)
下面是有关如何使用此方法的示例。您可以将其复制为实际游戏，它会起作用。
--[[ Some initial default settings. ]]
function love.load()
settings = {
mouseHitbox = 5, -- A diameter around the mouse cursor.
-- For a finger (thouchscreen) this could be bigger!
}
objects = {
[1] = {
x = 250, -- Initial X position of object.
y = 200, -- Initial Y position of object.
hitbox = 100, -- A diameter around the CENTER of the object.
isHit = false -- A flag for when the object has been hit.
},
[2] = {
x = 400,
y = 250,
hitbox = 250,
isHit = false
}
}
end
--[[ This is the actual function to detect collision between two objects. ]]
function collisionDetected(x1,y1,x2,y2,d1,d2)
-- Uses the x and y coordinates of two different points along with a diameter around them.
-- As long as these two diameters collide/overlap, this function returns true!
-- If d1 and/or d2 is missing, use the a default diameter of 1 instead.
local d1 = d1 or 1
local d2 = d2 or 1
local delta_x = x2 - x1
local delta_y = y2 - y1
local delta_d = (d1 / 2) + (d2 / 2)
if ( delta_x^2 + delta_y^2 < delta_d^2 ) then
return true
end
end
--[[ Now, some LÖVE functions to give the collisionDetection() some context. ]]
function love.draw()
for i=1,#objects do -- Loop through all objects and draw them.
if ( objects[i].isHit ) then
love.graphics.setColor(255, 0, 0) -- If an object is hit, it will flash red for a frame.
objects[i].isHit = false
else
love.graphics.setColor(255, 255, 255)
end
love.graphics.circle("line", objects[i].x, objects[i].y, objects[i].hitbox/2)
end
end
-- You can use the following to check, if any object has been clicked on (or tapped on a touch screen device).
function love.mousepressed(x,y,button)
if ( button == 1 ) then
local i = objectIsHit(x,y) -- Check, if an object has been hit.
if ( i ) then
-- The object number 'i' has been hit. Do something with this information!
objects[i].isHit = true
end
end
end
function objectIsHit(x,y)
for i=1,#objects do -- Loop through all objects and see, if one of them has been hit.
if ( collisionDetected(x, y, objects[i].x, objects[i].y, settings.mouseHitbox, objects[i].hitbox) ) then
return i -- This object has been hit!
end
end
end
-- For the sake of completeness: You can use something like the following to check, if the objects themselves collide.
-- This would come in handy, if the objects would move around the screen and then bounce from each other, for example.
function love.update(dt)
if ( collisionDetected(objects[1].x, objects[1].y, objects[2].x, objects[2].y, objects[1].hitbox, objects[2].hitbox) ) then
-- The objects collided. Do something with this information!
end
end
如您所见，collisionDetection() 函数使用起来非常简单直观。
希望我能给你更多的见解。 并与 LÖVE 2D 一起玩得开心！ :)
我一直在使用一些极其庞大的代码来检测简单对象之间的碰撞，而且我听说过边界框。我找不到任何关于如何使用它的教程，所以我在询问如何使用它。这是我检测碰撞的方法：
function platform.collision()
if player.x + player.width / 2 <= platform.x + platform.width and
player.x + player.width / 2 >= platform.x and
player.y + player.height <= platform.y + platform.height and
player.y + player.height >= platform.y then
MDN has a rather concise article on 2D collision detection。作为 MDN，示例在 javascript 中，但很容易翻译成任何语言并适用于任何语言 - 包括 Lua.
一起来看看：
Axis-Aligned Bounding Box
One of the simpler forms of collision detection is between two rectangles that are axis aligned — meaning no rotation. The algorithm works by ensuring there is no gap between any of the 4 sides of the rectangles. Any gap means a collision does not exist.
他们的例子，翻译成Lua：
local rect1 = { x = 5, y = 5, width = 50, height = 50 }
local rect2 = { x = 20, y = 10, width = 10, height = 10 }
if
rect1.x < rect2.x + rect2.width and
rect1.x + rect1.width > rect2.x and
rect1.y < rect2.y + rect2.height and
rect1.height + rect1.y > rect2.y
then
-- collision detected!
end
-- filling in the values =>
if
5 < 30 and
55 > 20 and
5 < 20 and
55 > 10
then
-- collision detected!
end
A live example，在 JavaScript 中再次证明了这一点。
这是一个快速（但不完美）的 Love2D 示例，您可以将其放入 main.lua 中并进行试验。
local function rect (x, y, w, h, color)
return { x = x, y = y, width = w, height = h, color = color }
end
local function draw_rect (rect)
love.graphics.setColor(unpack(rect.color))
love.graphics.rectangle('fill', rect.x, rect.y,
rect.width, rect.height)
end
local function collides (one, two)
return (
one.x < two.x + two.width and
one.x + one.width > two.x and
one.y < two.y + two.height and
one.y + one.height > two.y
)
end
local kp = love.keyboard.isDown
local red = { 255, 0, 0, 255 }
local green = { 0, 255, 0, 255 }
local blue = { 0, 0, 255, 255 }
local dim1 = rect(5, 5, 50, 50, red)
local dim2 = rect(20, 10, 60, 40, green)
function love.update ()
if kp('up') then
dim2.y = dim2.y - 1
end
if kp('down') then
dim2.y = dim2.y + 1
end
if kp('left') then
dim2.x = dim2.x - 1
end
if kp('right') then
dim2.x = dim2.x + 1
end
dim2.color = collides(dim1, dim2) and green or blue
end
function love.draw ()
draw_rect(dim1)
draw_rect(dim2)
end
Oka 解释得很好。这适用于所有矩形、未旋转和轴对齐的东西。你甚至已经这样做了。这非常适合按钮之类的东西！
但我喜欢做的是在物体周围使用（不可见的）圆圈，看看它们是否发生碰撞。这适用于高度与宽度大致相同的所有内容（许多横向卷轴平台游戏或自上而下的角色扮演游戏就是这种情况）。
如果你想让对象在当前位置居中，这是非常方便的。在触摸屏设备上模拟手指特别有用，因为手指比鼠标光标大很多。 ;)
下面是有关如何使用此方法的示例。您可以将其复制为实际游戏，它会起作用。
--[[ Some initial default settings. ]]
function love.load()
settings = {
mouseHitbox = 5, -- A diameter around the mouse cursor.
-- For a finger (thouchscreen) this could be bigger!
}
objects = {
[1] = {
x = 250, -- Initial X position of object.
y = 200, -- Initial Y position of object.
hitbox = 100, -- A diameter around the CENTER of the object.
isHit = false -- A flag for when the object has been hit.
},
[2] = {
x = 400,
y = 250,
hitbox = 250,
isHit = false
}
}
end
--[[ This is the actual function to detect collision between two objects. ]]
function collisionDetected(x1,y1,x2,y2,d1,d2)
-- Uses the x and y coordinates of two different points along with a diameter around them.
-- As long as these two diameters collide/overlap, this function returns true!
-- If d1 and/or d2 is missing, use the a default diameter of 1 instead.
local d1 = d1 or 1
local d2 = d2 or 1
local delta_x = x2 - x1
local delta_y = y2 - y1
local delta_d = (d1 / 2) + (d2 / 2)
if ( delta_x^2 + delta_y^2 < delta_d^2 ) then
return true
end
end
--[[ Now, some LÖVE functions to give the collisionDetection() some context. ]]
function love.draw()
for i=1,#objects do -- Loop through all objects and draw them.
if ( objects[i].isHit ) then
love.graphics.setColor(255, 0, 0) -- If an object is hit, it will flash red for a frame.
objects[i].isHit = false
else
love.graphics.setColor(255, 255, 255)
end
love.graphics.circle("line", objects[i].x, objects[i].y, objects[i].hitbox/2)
end
end
-- You can use the following to check, if any object has been clicked on (or tapped on a touch screen device).
function love.mousepressed(x,y,button)
if ( button == 1 ) then
local i = objectIsHit(x,y) -- Check, if an object has been hit.
if ( i ) then
-- The object number 'i' has been hit. Do something with this information!
objects[i].isHit = true
end
end
end
function objectIsHit(x,y)
for i=1,#objects do -- Loop through all objects and see, if one of them has been hit.
if ( collisionDetected(x, y, objects[i].x, objects[i].y, settings.mouseHitbox, objects[i].hitbox) ) then
return i -- This object has been hit!
end
end
end
-- For the sake of completeness: You can use something like the following to check, if the objects themselves collide.
-- This would come in handy, if the objects would move around the screen and then bounce from each other, for example.
function love.update(dt)
if ( collisionDetected(objects[1].x, objects[1].y, objects[2].x, objects[2].y, objects[1].hitbox, objects[2].hitbox) ) then
-- The objects collided. Do something with this information!
end
end
如您所见，collisionDetection() 函数使用起来非常简单直观。
希望我能给你更多的见解。 并与 LÖVE 2D 一起玩得开心！ :)