XNA 拋物線運動(Projectile Motion)

2011-10-25

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很多遊戲都會用到拋物線運動，像大砲射擊、生氣鳥等，在這裡我們要運用國中學的物裡公式來實作程式碼。

Vx = Vx

Vy = Vy + a*t

X = X + Vx*t

Y = Y + Vy*t + 1/2*a*t*^2

先將小球圖片加入專案裡

在Game1類別宣告相關變數

Public Class Game1

    Inherits Microsoft.Xna.Framework.Game

    Private WithEvents graphics As GraphicsDeviceManager

    Private WithEvents spriteBatch As SpriteBatch

    Dim ball As Texture2D

    Dim position As Vector2 = New Vector2(0, 450)   '位置

    Dim velocity As Vector2 = New Vector2(7, -30)   '速度   (pixel/frame)

    Dim acceleration As Integer = 1                 '加速度 (pixel/frame^2)

End Class

LoadContent()載入小球圖片資源

Protected Overrides Sub LoadContent()

        ' Create a new SpriteBatch, which can be used to draw textures.

        spriteBatch = New SpriteBatch(GraphicsDevice)

        ' TODO: use Me.Content to load your game content here

        ball = Content.Load(Of Texture2D)("ball")

End Sub

我們在Update()裡實作物裡公式:

Vx = Vx

Vy = Vy + a*t

X = X + Vx*t

Y = Y + Vy*t + 1/2*a*t*^2

這裡時間 t = 1 frame


Protected Overrides Sub Update(ByVal gameTime As GameTime)
        ' Allows the game to exit
        If GamePad.GetState(PlayerIndex.One).Buttons.Back = ButtonState.Pressed Then
            Me.Exit()
        End If

        ' TODO: Add your update logic here
        velocity.Y += acceleration

        position.X += velocity.X
        position.Y = position.Y + velocity.Y + CInt(0.5 * acceleration)

        MyBase.Update(gameTime)
End Sub

在Draw()繪製小球

Protected Overrides Sub Draw(ByVal gameTime As GameTime)

        GraphicsDevice.Clear(Color.CornflowerBlue)

        ' TODO: Add your drawing code here

        spriteBatch.Begin()

        spriteBatch.Draw(ball, position, Color.White)

        spriteBatch.End()

        MyBase.Draw(gameTime)

End Sub

程式執行結果如下，接下來是碰撞偵測喔! (範例下載)

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