如果我使用以下内容
for(int i = 255; i > 0; i--)
{
Color transparentBlack = new Color(0,i);
}
我有使用这种颜色的对象的效果,从黑色到浅灰色绘制,然后当alpha值变为零时不可见.但是,如果我以白色值开头：
new Color(255,255,i);
物体永远不会变得不可见,只会保持白色.我还注意到,如果我使用的值比黑色(比如50,50,50)轻一点,那么绘图就会从黑暗变为隐形,变为白色.
我假设我只是不明白alpha混合混合是如何工作的,但有没有办法使白色渐变为半透明？
编辑：我正在绘制的背景是Color.CornflowerBlue(100,149,237,255)
编辑：示例XNA程序再现说明.使用;创建一个新的XNA Game Studio 4.0项目 – Windows游戏(4.0),称之为AlphaBlendTest – &在内容项目中添加一个新的SpriteFont并将其命名为testfont
using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Audio;
using Microsoft.Xna.Framework.Content;
using Microsoft.Xna.Framework.GamerServices;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
using Microsoft.Xna.Framework.Media;
namespace AlphaBlendTest
{
/// <summary>
/// This is the main type for your game
/// </summary>
public class Game1 : Microsoft.Xna.Framework.Game
{
GraphicsDeviceManager graphics;
SpriteBatch spriteBatch;
SpriteFont font;
public Game1()
{
graphics = new GraphicsDeviceManager(this);
Content.RootDirectory = "Content";
}
/// <summary>
/// Allows the game to perform any initialization it needs to before starting to run.
/// This is where it can query for any required services and load any non-graphic
/// related content. Calling base.Initialize will enumerate through any components
/// and initialize them as well.
/// </summary>
protected override void Initialize()
{
// TODO: Add your initialization logic here
base.Initialize();
}
/// <summary>
/// LoadContent will be called once per game and is the place to load
/// all of your content.
/// </summary>
protected override void LoadContent()
{
// Create a new SpriteBatch,which can be used to draw textures.
spriteBatch = new SpriteBatch(GraphicsDevice);
font = Content.Load<SpriteFont>("testfont");
}
/// <summary>
/// UnloadContent will be called once per game and is the place to unload
/// all content.
/// </summary>
protected override void UnloadContent()
{
// TODO: Unload any non ContentManager content here
}
/// <summary>
/// Allows the game to run logic such as updating the world,/// checking for collisions,gathering input,and playing audio.
/// </summary>
/// <param name="gameTime">Provides a snapshot of timing values.</param>
protected override void Update(GameTime gameTime)
{
// Allows the game to exit
if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
this.Exit();
// TODO: Add your update logic here
base.Update(gameTime);
}
/// <summary>
/// This is called when the game should draw itself.
/// </summary>
/// <param name="gameTime">Provides a snapshot of timing values.</param>
protected override void Draw(GameTime gameTime)
{
GraphicsDevice.Clear(Color.CornflowerBlue);
spriteBatch.Begin();
//spriteBatch.Draw(tR,new Rectangle(100,100,100),Color.Red);
Vector2 v2 = new Vector2(0,0);
spriteBatch.DrawString(font,"Test - White",v2,Color.White);
v2.Y = v2.Y + 50;
spriteBatch.DrawString(font,"Test - Black",Color.Black);
v2.Y = v2.Y + 50;
Color BlackTransparent = new Color(0,"Test - Black Transparent",BlackTransparent);
v2.Y = v2.Y + 50;
Color WhiteTransparent = new Color(255,"Test - White Transparent",WhiteTransparent);
spriteBatch.End();
base.Draw(gameTime);
}
}
}
编辑：这是此代码绘制的图像：
编辑：其中一条评论涉及这是一个仅与文本相关的Windows功能.我以文本为例来保持演示程序的小巧;使用图像进行测试会得到相同的结果.
将方框添加到演示程序中;创建一个方形白色PNG图像并将其添加到内容目录(使用内容管道的默认值).然后将其添加到类中：
Texture2D tWhiteBox;
将其添加到load方法中：
tWhiteBox = Content.Load<Texture2D>("whitebox");
然后在绘图中添加以下其他绘图语句：
v2.Y = v2.Y + 50; spriteBatch.Draw(tWhiteBox,WhiteTransparent);
解决方法
灰色是XNA 4.0中的颜色(如果您尝试仅调整Alpha通道而不调整RGB通道,则为全白色).使用预乘的alpha完成透明度(默认情况下).如果您正在寻找旧的非预先XNA 3.1行为,请参阅Shawn Hargreaves的这篇文章：
http://blogs.msdn.com/b/shawnhar/archive/2010/04/08/premultiplied-alpha-in-xna-game-studio-4-0.aspx.在帖子的底部,它告诉你如何做到这一点.
我建议在这之前阅读他所有关于预乘alpha的帖子(你可以使用他页面顶部左侧的“Blog Index”链接) – pre-mul真的好多了在逻辑上更一致.
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