如果我使用以下内容
for(int i = 255; i > 0; i--)
{
Color transparentBlack = new Color(0, 0, 0, i);
}
我有使用这种颜色绘制的对象的效果,从黑色变为浅灰色,然后当 alpha 值变为零时不可见。但是,如果我从白色值开始:
new Color(255, 255, 255, i);
对象永远不会变得不可见,只会保持白色。我还注意到,如果我使用比黑色稍浅的值(比如 50、50、50),绘图会从深色变为不可见,再变为白色。
我假设我只是不明白 alpha 混合是如何工作的,但是有没有办法让白色逐渐变成半透明?
编辑:我绘制的背景是 Color.CornflowerBlue (100,149,237,255)
编辑:再现解释的示例 XNA 程序。使用;创建一个新的 XNA Game Studio 4.0 项目 - Windows Game (4.0),将其命名为 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, 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);
}
}
}
编辑:这是这段代码绘制的图像:
编辑:其中一条评论担心这是一个仅与文本相关的窗口“功能”。我使用文本作为例子来保持演示程序的小;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;
将此添加到加载方法中:
tWhiteBox = Content.Load<Texture2D>("whitebox");
然后在 draw 中的其他 draw 语句下面添加以下内容:
v2.Y = v2.Y + 50;
spriteBatch.Draw(tWhiteBox, v2, WhiteTransparent);
最佳答案
灰色是您在 XNA 4.0 中得到的(如果您尝试只调整 alpha channel 而不同时调整 RGB channel ,则为全白色)。透明度是使用预乘 alpha 完成的(默认情况下)。如果您正在寻找旧的非 pre-mul 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,它会告诉您如何操作。
我建议在阅读之前先阅读他关于预乘 alpha 的所有帖子(您可以使用他页面顶部附近左侧的“博客索引”链接)- pre-mul 确实很多更好,逻辑上更一致。
关于c# - 是否存在使白色不可见的 alpha 值?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/3849569/