A very simple birds animation

For beginners, the code using basic function in Codea without tween().

Every line with comment -- using my poor English...

Xcode project file：

http://pan.baidu.com/s/1eQowhRs

code:

-- main
-- Use this function to perform your initial setup
function setup()

    displayMode(FULLSCREEN)

    x = WIDTH/2
    y = HEIGHT/2
    img = sprite("Cargo Bot:Starry Background")

    -- 第一只 mesh 鸟 -- The 1st mesh bird  
    myMeshBird1 = mesh()

    -- 第二只 mesh 鸟 -- The 2nd mesh bird   
    myMeshBird2 = mesh()
    myMeshBird2.texCoords = {vec2(0,0),vec2(0,1),vec2(1,1),vec2(0,0),vec2(1,1),vec2(1,0)}
    myMeshBird2.texture = img

    -- 第三只 mesh 鸟 -- The 3rd mesh bird    
    myMeshBird3 = mesh()

    -- 用于控制循环的变量 -- variable for loop control    
    i, j = 0, 0
    k = 1
    m, n = 1000, 1
    a, b = 255, 1

    parameter.integer("i",0,150,0)
    parameter.integer("j",0,150,0)   
    parameter.integer("k",-1,1,1)
    parameter.integer("m",0,2000,1000)  
    parameter.integer("n",-5,5,1)
    parameter.integer("a",0,255,255)  
    parameter.integer("b",-1,1,1)    

    parameter.integer("l1",100,300,200)
    parameter.integer("h1",100,300,200)    
    parameter.integer("l2",10,200,60)
    parameter.integer("h2",0,100,10)    

    -- 三只对象实例鸟 -- Three object instance birds
    myBird1 = Bird(x,y)
    myBird2 = Bird(x+50,y)
    myBird3 = Bird(x,y)
end

-- This function gets called once every frame
function draw()

    -- 用来设置颜色渐变效果 -- Color alpha control    
    -- Alpha channel has a maximum of 255
    local alpha = math.min(ElapsedTime * 20%255, 255) 
    -- Set tint using tint(grey, alpha)
    tint(255,alpha)                              

    -- 用 tint() 函数控制色彩透明度变化 -- Use tint()
    if alpha == 255 then 
        tint(0,alpha)
    elseif alpha == 50 then 
        tint(255,alpha) 
    end    

    -- 控制翅膀坐标变化 -- control change of wings' coords  
    -- 若 i 达到最大值，则把步长 k 设置为 -1，i + k 值会递减 
    -- when i become max, set step k to -1, i+k will decrease
    -- 若 i 达到最小值，则把步长 k 设置为 1，i + k 值会递增  
    -- when i become min, set step k to 1, i+k will increase 
    -- 当 i 最大时调用声音，以保证声音和动作同步   
    -- load sound while i become max , to make sure sound and motion synchronize
    if i == 150 then
        k = -1
        sound("A Hero's Quest:Walk 2 (Short)")
    elseif i == 0 then 
        k = 1
    end

    -- 控制缩放 -- contrl scale 
    if m == 1500 then n = -1 elseif m == 0 then n = 1 end

    -- 用变量 a，b 直接控制色彩透明度变化 
    -- use variable a,b to control change of color's alpha directly
    if a == 255 then b = -1 elseif a == 50 then b = 1 end

    -- 开始递增或递减 -- start increase or decrease
    i = i + 5 * k
    j = j + 8 * k
    m = m + 2 * n
    a = a + b 

    -- 设置背景色 -- set background color 
    background(11, 11, 10, 86)

    -- 设置背景参照物 -- set background object 
    pushStyle()
    pushMatrix()
    -- scale(m/500,m/500)
    -- translate(-m,m)
    fill(255, 0, 0, alpha)
    stroke(255, 118, 0, alpha)
    ellipse(500,1250-m,m-350)
    popMatrix()
    popStyle()

    -- 用于三只 mesh 鸟的颜色 -- colors of three mesh birds 
    myColor1 = color(255, 255, 0, alpha)
    myColor2 = color(79, 255, 0, a)
    myColor3 = color(79, 2, 100, a)    

    -- 构成飞鸟线条的顶点坐标 -- vertex coords of bird line 
    -- vec2 向量 p1(0,0) 为中心点提供坐标 -- vec(0,0) is the central point 
    p1 = vec2(0,0)
    -- 组成右边翅膀的顶点 -- vertices of right wing 
    -- p2, p3 = vec2(200+i/8,-150+2*j),vec2(60-i/3,10+j/3)
    p2, p3 = vec2(l1+i/8,-150+2*j),vec2(l2-i/3,h2+j/3)
    -- 组成左边翅膀的顶点 -- vertices of left wing 
    -- p4, p5 = vec2(-200-i/8,-150+2*j),vec2(-60+i/3,10+j/3)
    p4, p5 = vec2(-200-i/8,-150+2*j),vec2(-60+i/3,10+j/3)

    -- 用这些坐标设置 mesh 的顶点 -- set mesh vertices 
    myMeshBird1.vertices = {p1, p2, p3, p1, p4, p5}
    myMeshBird2.vertices = {p1, p2, p3, p1, p4, p5}    
    myMeshBird3.vertices = {p1, p2, p3, p1, p4, p5}    

    -- 平移 
    translate(3*x/4,3*y/4)

    -- 整体循环缩放全部飞鸟比例，产生鸟群距离变化的感觉 
    -- total birds loop scale, to feel birds distance changing 
    scale(m/1500)

    -- 直接用 line() 函数画的飞鸟 -- use line() draw bird directly
    pushMatrix()     
    pushStyle()
    translate(x/2,y)   
    scale(3)
    stroke(0, 39, 255, 255)
    strokeWidth(5)

    -- 右边翅膀线条 -- lines of right wing 
    line(p1[1],p1[2],p2[1],p2[2])
    line(p1[1],p1[2],p3[1],p3[2])
    line(p3[1],p3[2],p2[1],p2[2])
    -- 左边翅膀线条 -- lines of right wing
    line(p1[1],p1[2],p4[1],p4[2])
    line(p1[1],p1[2],p5[1],p5[2])
    line(p4[1],p4[2],p5[1],p5[2])    
    -- 用文字标出飞鸟的编号 -- print bird's No.
    fill(0, 51, 255, 255)
    -- text("零号鸟",p1[1],p1[2])
    text("1",p1[1],p1[2])       
    popStyle()
    popMatrix()

    -- 用 class Bird 绘制的对象实例鸟 -- object instance bird drawing with class Bird 
    pushMatrix()
    pushStyle()
    -- myBird.deltaX = myBird.deltaX + 5*k
    -- myBird.deltaY = myBird.deltaY + 5*k
    rotate(m)
    scale(0.2)
    myBird1:setColors(myColor)
    myBird1:draw()   
    popStyle() 
    popMatrix()

    -- 用 class Bird 绘制的对象实例鸟 -- object instance bird drawing with class Bird 
    pushMatrix()
    pushStyle()
    rotate(-m)
    scale(0.3)
    myBird2:setColors(myColor)
    myBird2:draw()   
    popStyle() 
    popMatrix()

    -- 用 class Bird 绘制的对象实例鸟 -- object instance bird drawing with class Bird 
    pushMatrix()
    pushStyle()
    rotate(-m)
    scale(0.3)
    myBird3:setColors(myColor2)
    myBird3:draw()   
    popStyle() 
    popMatrix()

    -- 用 mesh 绘制的一号飞鸟 -- No.1 mesh bird 
    pushMatrix()
    pushStyle()
    translate(-x/4,-y/2)
    scale(.8)
    myMeshBird1:setColors(myColor1)
    -- myMeshBird1.shader.time = ElapsedTime*5
    myMeshBird1:draw()
    -- 用文字标出飞鸟的编号  -- print bird's No.      
    fill(173, 255, 0, 255)
    -- text("一号鸟",p1[1],p1[2])
    text("1",p1[1],p1[2])    
    popStyle()
    popMatrix()

    -- 用 mesh 绘制的二号飞鸟 -- No.1 mesh bird 
    pushMatrix()
    pushStyle()
    translate(300,200)
    scale(.5)
    myMeshBird2:setColors(myColor2)
    myMeshBird2:draw()
    -- 用文字标出飞鸟的编号  -- print bird's No. 
    fill(63, 218, 26, 255)
    -- text("二号鸟",p1[1],p1[2])
    text("2",p1[1],p1[2])        
    popStyle()    
    popMatrix()

    -- 用 mesh 绘制的三号飞鸟 -- No.1 mesh bird 
    pushMatrix()
    pushStyle()
    translate(30,80)
    scale(2)
    myMeshBird3:setColors(myColor3)
    myMeshBird3:draw()
    -- 用文字标出飞鸟的编号  -- print bird's No.   
    fill(218, 25, 197, 255)
    -- text("三号鸟",p1[1],p1[2])
    text("3",p1[1],p1[2])        
    popStyle()    
    popMatrix()

end

-- Bird class
Bird = class()

function Bird:init(x,y)
    -- you can accept and set parameters here
    -- 最初的位置坐标 -- bird's position
    self.x = x
    self.y = y
    -- 最初的坐标偏移量 -- bird's offset 
    self.deltaX = 0
    self.deltaY = 0 

    self.i1, self.j1 = 0, 0
    self.k1 = 1 

    flag = mesh()   

    myColor = color(55, 172, 172, 255)
    Bird:setColors(myColor) 
end

function Bird:draw()
    -- Codea does not automatically call this method

    if self.i1 == 150 then
        self.k1 = -1
    elseif i == 0 then 
        self.k1 = 1
    end

    self.i1 = self.i1 + 5 * self.k1
    self.j1 = self.j1 + 8 * self.k1

    self.deltaX = self.i1
    self.deltaY = self.j1

    flag.vertices = {
        vec2(self.x,self.y),
        vec2(self.x + 200 - self.deltaX/8, self.y - 150 + self.deltaY * 2),
        vec2(self.x + 60 - self.deltaX/3, self.y + 10+self.deltaY/3),
        vec2(self.x,self.y),
        vec2(self.x - 200 + self.deltaX/8, self.y - 150 + self.deltaY * 2), 
        vec2(self.x - 60 + self.deltaX/3, self.y + 10 + self.deltaY/3),
    }
    -- Bird:setColors(myColor)
    fill(24, 218, 201, 255)
    -- text("对象鸟",self.x,self.y)
    text("Object Instance Bird",self.x,self.y)        
    flag:draw()    
end

function Bird:setColors(colors)
    flag:setColors(colors)
end

function Bird:touched(touch)
    -- Codea does not automatically call this method
end