c# – 是否存在使白色变为隐形的alpha值？

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);