粒子系統(tǒng)通常用于三維場景中進(jìn)行真實環(huán)境模擬，比如第四節(jié)的天氣系統(tǒng)。天氣的實現(xiàn)是粒子系統(tǒng)最重要的應(yīng)用領(lǐng)域之一，所有的一切無論是云、雨、霧，還是落葉、隕石及閃電，都可視作基礎(chǔ)粒子；除此之外，游戲中常常還會用到粒子系統(tǒng)來渲染像發(fā)光、軌跡等抽象效果。當(dāng)然，有時簡單并不意味著就不能締造奇跡，比如本節(jié)大家將要看到的就是基于簡單粒子系統(tǒng)所創(chuàng)建的當(dāng)下主流2.5D RPG中極其拉風(fēng)之裝備粒子發(fā)散動畫特效。

　　 一提到Silverlight中的粒子，首先想到的肯定是WriteableBitmap。沒錯，今天的主角就是它，讓人又愛又恨的WriteableBitmap。愛，因為它可以對Silverlight中任意UI對象進(jìn)行基于像素級別的處理，這意味著只要想得出的效果肯定能實現(xiàn)；正因如此，對其恨之入骨則因為WriteableBitmap在目前的版本中還暫時無法得到GPU硬件加速的支持，其功能偏少，性能也有待進(jìn)一步提高。

　　僅當(dāng)為了Silverlight 5 的登場打基礎(chǔ)，借鑒《降龍之劍》中的裝備粒子系統(tǒng)，我們同樣可以通過非常簡單的代碼編寫出極度拉風(fēng)的粒子發(fā)射動畫特效。

　　于是我們得首先準(zhǔn)備基礎(chǔ)粒子素材，比如希望武器會冒著火光，亦或者你希望鎧甲能寒冰四散等，那么我們每樣準(zhǔn)備3張或更多的圖片，通過隨即的方式呈現(xiàn)便可達(dá)到相當(dāng)逼真的效果：

　　接下來的問題是這些粒子該如何以精確的裝備部件實體區(qū)域為起點進(jìn)行發(fā)射？

　　用WriteableBitmap對每幀圖片進(jìn)行寬*高數(shù)量像素的逐個掃描？試想如果角色的尺寸是500*500=250000，那么每間隔幾百毫秒都要遍歷幾十萬的像素，UI線程不卡死才怪(順便提一下，UI卡死的罪魁禍?zhǔn)拙褪茄h(huán)，在UI線程中應(yīng)盡量減少循環(huán)次數(shù)或巧妙的進(jìn)行分解與規(guī)避)。其實我們完全可以采用隨機(jī)抽樣的方案，比如每次對其中的1000個像素進(jìn)行抽樣檢查，當(dāng)其A值（透明度）不為0時則表示該像素正處于裝備部件的實體區(qū)域中。接下來便可仿造流光追影的類似效果，通過WriteableBitmap對目標(biāo)裝備部件首先進(jìn)行復(fù)制，然后按照如上方式隨機(jī)抽取部分裝備實體上的粒子進(jìn)行發(fā)射飄散:

/// <summary>
/// 顯示風(fēng)中粒子
/// </summary>
/// <param name="role">所修飾角色</param>
/// <param name="equipType">所參照的裝備</param>
/// <param name="particleType">粒子類型</param>
/// <param name="color">顏色</param>
/// <param name="amount">量</param>
public void ShowWindParticles(Hero role, EquipTypes equipType, ParticleTypes particleType, Color color, double amount) {
    int distance = 0;
    double speed = 0;
    if (role.Action == Actions.Stop) {
        distance = 40;
        speed = RandomSeed.Next(2000, 3000) * 0.01;
    } else {
        distance = 40;
        speed = RandomSeed.Next(1000, 1500) * 0.01;
    }
    int halfDistance = distance / 2;
    int obliqueDistance = distance * 2 / 3;
    string particleName = string.Empty;
    switch (particleType) {
        case ParticleTypes.Normal:
            particleName = "Particle";
            break;
        case ParticleTypes.Smoke:
            particleName = "Smoke";
            break;
        case ParticleTypes.Ice:
            particleName = "Ice";
            break;
        case ParticleTypes.Spark:
            particleName = "Spark";
            break;
    }
    Dispatcher.BeginInvoke(delegate {
        ObjectBase equip = role.EquipEntity(equipType);
        WriteableBitmap writeableBitmap = new WriteableBitmap(equip, null);
        lock (writeableBitmap) {
            writeableBitmap.Invalidate();
            int z = 0;
            if (equipType == EquipTypes.Weapon) {
                z = role.Z + equip.Z;
            } else {
                z = (role.Direction == Directions.North || role.Direction == Directions.NorthEast || role.Direction == Directions.NorthWest) ? role.Z : role.Z - 20;
            }
            Point position = equipType == EquipTypes.Overall ? role.Center : equip.Position;
            Point2D destination = new Point2D();
            MonoChrome monoChrome = new MonoChrome() { FilterColor = color };
            switch (role.Direction) {
                case Directions.North:
                    destination.X = 0; destination.Y = RandomSeed.Next(halfDistance, distance);
                    break;
                case Directions.NorthEast:
                    destination.X = -RandomSeed.Next(halfDistance, obliqueDistance); destination.Y = RandomSeed.Next(halfDistance, obliqueDistance);
                    break;
                case Directions.East:
                    destination.X = -RandomSeed.Next(halfDistance, distance); destination.Y = 0;
                    break;
                case Directions.SouthEast:
                    destination.X = -RandomSeed.Next(halfDistance, obliqueDistance); destination.Y = -RandomSeed.Next(halfDistance, obliqueDistance);
                    break;
                case Directions.South:
                    destination.X = 0; destination.Y = -RandomSeed.Next(halfDistance, distance);
                    break;
                case Directions.SouthWest:
                    destination.X = RandomSeed.Next(halfDistance, obliqueDistance); destination.Y = -RandomSeed.Next(halfDistance, obliqueDistance);
                    break;
                case Directions.West:
                    destination.X = RandomSeed.Next(halfDistance, distance); destination.Y = 0;
                    break;
                case Directions.NorthWest:
                    destination.X = RandomSeed.Next(halfDistance, obliqueDistance); destination.Y = RandomSeed.Next(halfDistance, obliqueDistance);
                    break;
            }
            for (int i = 0; i < amount; i++) {
                int x = RandomSeed.Next(0, writeableBitmap.PixelWidth);
                int y = RandomSeed.Next(0, writeableBitmap.PixelHeight);
                byte[] bytes = BitConverter.GetBytes(writeableBitmap.Pixels[writeableBitmap.PixelWidth * y + x]);
                if (bytes[3] != 0) {
                    Particle particle = new Particle() { Effect = monoChrome, Z = z, Source = GlobalMethod.GetProjectImage(string.Format("UI/{0}{1}.png", particleName, RandomSeed.Next(0, 3))) };
                    space.Children.Add(particle);
                    EventHandler handler = null;
                    particle.Disposed += handler = (s, e) => {
                        Particle p = s as Particle;
                        p.Disposed -= handler;
                        space.Children.Remove(p);
                    };
                    particle.Move(new Point(role.Position.X - position.X + x, role.Position.Y - position.Y + y), new Point(role.Position.X - position.X + x + destination.X, role.Position.Y - position.Y + y + destination.Y), speed, MoveModes.Opacity);
                }
            }
        }
    });
}        

        

        
        
      
        
NET技術(shù)：Silverlight 2.5D RPG游戲技巧與特效處理：（九）粒子系統(tǒng)，轉(zhuǎn)載需保留來源！
        
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