Unity3D Shader实现动态屏幕遮罩

屏幕可视范围跟随目标物体移动，可修改可视范围大小，边缘渐变大小、以及遮罩颜色，支持最高物体数量可在shader中修改，当前版本支持最多9个物体。

效果图如下：

控制面板如下：

shader代码如下：

shader "peter/darkeffect"
{
  properties
  {
    _maintex ("texture", 2d) = "white" {}
  }

  subshader
  {
    // no culling or depth
    cull off zwrite off ztest always

    pass
    {
      cgprogram
      #pragma vertex vert
      #pragma fragment frag

      #include "unitycg.cginc"

      //追踪物体最多个数
      #define itemsize 9

      struct appdata
      {
        float4 vertex : position;
        float2 uv : texcoord0;
      };

      struct v2f
      {
        float2 uv : texcoord0;
        float4 vertex : sv_position;
      };

      sampler2d _maintex;

      fixed4 _darkcolor;
      float _smoothlength;
      fixed _itemcnt;
      float4 _item[itemsize];

      v2f vert (appdata v)
      {
        v2f o;
        o.vertex = unityobjecttoclippos(v.vertex);
        o.uv = v.uv;
        return o;
      }

      fixed calcalpha(float4 vt, float4 pt)
      {
        if(pt.z < 0)
        {
          return 1;
        }

        float distpow2 = pow(vt.x - pt.x, 2) + pow(vt.y - pt.y, 2);
        float dist = (distpow2 > 0) ? sqrt(distpow2) : 0;

        float smoothlength = _smoothlength;
        if(smoothlength < 0)
        {
          smoothlength = 0;
        }

        float maxvalue = pt.z;
        float minvalue = pt.z - smoothlength;
        if(minvalue < 0)
        {
          minvalue = 0;
          smoothlength = pt.z;
        }

        if(dist <= minvalue)
        {
          return 0;
        }
        else if (dist > maxvalue)
        {
          return 1;
        }

        fixed retval = (dist - minvalue) / smoothlength;

        return retval;
      }

      fixed4 frag (v2f i) : sv_target
      {
        fixed alphaval = 1;
        fixed tmpval = 1;

        for(fixed index = 0; index < _itemcnt; ++index)
        {
          tmpval = calcalpha(i.vertex, _item[index]);
          if(tmpval < alphaval)
          {
            alphaval = tmpval;
          }
        }

        alphaval *= _darkcolor.a;

        return tex2d(_maintex, i.uv) * ( 1 - alphaval) + _darkcolor * alphaval;
      }

      endcg
    }
  }
}

c#调用代码如下：

using system.collections;
using system.collections.generic;
using unityengine;

[executeineditmode]
[requirecomponent(typeof(camera))]
public class darkeffect : monobehaviour
{
  [system.serializable]
  public class item
  {
    [serializefield]
    public transform target;

    [serializefield]
    public int radius;

    public vector3 getscreenposition(camera cam)
    {
      return cam.worldtoscreenpoint(target.position);
    }
  }

  //渐变像素数量
  public int _smoothlength = 20;
  //遮罩混合颜色
  public color _darkcolor = color.black;
  //目标物体
  public list<item> _items = new list<item>();

  protected material _mainmaterial;
  protected camera _maincamera;

  vector4[] _itemdatas;
  item _tmpitem;
  vector4 _tmpvt;
  vector3 _tmppos;
  int _tmpscreenheight;

  private void onenable()
  {
    _mainmaterial = new material(shader.find("peter/darkeffect"));
    _maincamera = getcomponent<camera>();
  }

  private void onrenderimage(rendertexture source, rendertexture destination)
  {

    if (_itemdatas == null || _itemdatas.length != _items.count)
    {
      _itemdatas = new vector4[_items.count];
    }

    _tmpscreenheight = screen.height;

    for (int i = 0; i < _items.count; i++)
    {
      _tmpitem = _items[i];
      _tmppos = _tmpitem.getscreenposition(_maincamera);

      _tmpvt.x = _tmppos.x;
      _tmpvt.y = _tmpscreenheight - _tmppos.y;
      _tmpvt.z = _tmpitem.radius;
      _tmpvt.w = 0;

      _itemdatas[i] = _tmpvt;
    }

    _mainmaterial.setint("_smoothlength", _smoothlength);
    _mainmaterial.setcolor("_darkcolor", _darkcolor);
    _mainmaterial.setint("_itemcnt", _itemdatas.length);
    _mainmaterial.setvectorarray("_item", _itemdatas);

    graphics.blit(source, destination, _mainmaterial);
  }
}

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