有没有一个alpha值使白色变为不可见的?

如果我用下面的

for(int i = 255; i > 0; i--)
{
    Color transparentBlack = new Color(0, 0, 0, i);
}

new Color(255, 255, 255, i);

物体永远不会变的看不见,只会保持白色。我还注意到,如果我使用一个比黑色稍浅的值(比如50,50,50),绘图会从黑色变为不可见,再变为白色。

我想我只是不明白alpha混合是如何工作的,但是有没有办法让白色褪色为半透明呢?

编辑:我画的背景是颜色:矢车菊蓝(100,149,237,255)

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, 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", v2, Color.Black);

        v2.Y = v2.Y + 50;

        Color BlackTransparent = new Color(0, 0, 0, 0);
        spriteBatch.DrawString(font, "Test - Black Transparent", v2, BlackTransparent);

        v2.Y = v2.Y + 50;
        Color WhiteTransparent = new Color(255, 255, 255, 0);
        spriteBatch.DrawString(font, "Test - White Transparent", v2, WhiteTransparent);

        spriteBatch.End();

        base.Draw(gameTime);
    }
}
}

要将方形框添加到演示程序中,请创建一个方形的白色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;

将此添加到load方法中:

tWhiteBox = Content.Load<Texture2D>("whitebox");

v2.Y = v2.Y + 50;
spriteBatch.Draw(tWhiteBox, v2, WhiteTransparent);