unity下贴图混合（Texture Blending）

在unity制作自定义时，经常会遇到自定义妆容等问题，美术会提供大量的眉毛/胡子/腮红等贴图，来供用户选择。

美术给出的眉毛的小贴图如下:

在用户选用不同的胡子眉毛，可以将选定的小贴图和皮肤base贴图进行融合，得到完整的Character贴图。

       

Method1：CPU端逐像素根据alpha通道进行叠加。

public void MergeTexture_(Texture2D tt1, Texture2D tt2, int offsetX, int offsetY)
        {

            Texture2D newTex = new Texture2D(tt1.width, tt1.height, TextureFormat.ARGB32, false);

            newTex.SetPixels(tt1.GetPixels());

            for (int x = ; x < tt2.width; x++)
            {
                for (int y = ; y < tt2.height; y++)
                {
                    var PixelColorFore = tt2.GetPixel(x, y) * tt2.GetPixel(x, y).a;
                    var newY = tt1.height - offsetY - tt2.height + y;
                    var PixelColorBack = tt1.GetPixel(x + offsetX, newY) * tt1.GetPixel(x + offsetX, newY).a;
                    newTex.SetPixel(x + offsetX, newY, PixelColorFore+ PixelColorBack);
                }
            }
            newTex.Apply();
             System.IO.File.WriteAllBytes(Application.dataPath + "/" + tt1.name + ".png", newTex.EncodeToPNG());
            GameObject.Find("obj001").GetComponent<Renderer>().material.mainTexture = newTex;
        }

这里注意下，由于需要对Texture进行读取像素，因此需要将相应的Texture设置为Read/Write Enabled，否则会报错。

逐像素操作可以用unity内置函数改为块操作，经过测试，能大概少一半的耗时

 public void MergeTexture(Texture2D tt1, Texture2D tt2, int offsetX, int offsetY)
         {

             Texture2D newTex= new Texture2D(tt1.width, tt1.height, TextureFormat.ARGB32, false);

             newTex.SetPixels(tt1.GetPixels());
             Color32[] colors = tt2.GetPixels32();
             // tt1.
             newTex.SetPixels32(offsetX, tt1.height - offsetY - tt2.height,tt2.width,tt2.height, colors,);
             newTex.Apply();
             GameObject.Find("obj001").GetComponent<Renderer>().material.mainTexture = newTex;
         }

上述方案基本上是在CPU端进行的，实际上可以调用Unity的底层绘制接口在GPU上进行操作，主要是利用RenderTexture和Graphics.DrawTexture()进行操作

 public Texture2D texture;        //Starting image.
    public Texture2D stampTexture;   //Texture to Graphics.Drawtexture on my RenderTexture.
    public float posX = 256f;        //Position the DrawTexture command while testing.
    public float posY = 256f;        //Position the DrawTexture command while testing.
    RenderTexture rt;                //RenderTexture to use as buffer.

    void Start()
    {
        rt = new RenderTexture(, , );           //Create RenderTexture 512x512 pixels in size.
        GameObject.Find("obj001").GetComponent<Renderer>().material.mainTexture = rt;   //Assign my RenderTexure to be the main texture of my object.
        RenderTexture.active = rt;
        Graphics.Blit(texture, rt);          //Blit my starting texture to my RenderTexture.
        RenderTexture.active = rt;                      //Set my RenderTexture active so DrawTexture will draw to it.
        GL.PushMatrix();                                //Saves both projection and modelview matrices to the matrix stack.
        GL.LoadPixelMatrix(, , , );            //Setup a matrix for pixel-correct rendering.
                                                         //Draw my stampTexture on my RenderTexture positioned by posX and posY.
        Graphics.DrawTexture(new Rect(posX, posY, stampTexture.width, stampTexture.height), stampTexture);
        Texture2D png = new Texture2D(rt.width, rt.height, TextureFormat.ARGB32, false);
        png.ReadPixels(new Rect(, , rt.width, rt.height), , );
        System.IO.File.WriteAllBytes(Application.dataPath + "/" + "nihao.png", png.EncodeToPNG());
        GL.PopMatrix();
        //Restores both projection and modelview matrices off the top of the matrix stack.
        RenderTexture.active = null;                    //De-activate my RenderTexture.