對屏幕特定部分進行後期特效處理

最近在做一個效果：用一條線將整個屏幕分成兩部分，一部分是灰色，一部分是彩色，線的位置是可變的

如果只是區分的話，簡單的方法就是相機前加一個灰色quad，如下圖，但明顯不如灰化對比度高

下面就來實現這個功能
首先，我們要建一個屏幕特效腳本掛在到相機上

[C#] 純文本查看複製代碼

using

System; 

using

UnityEngine; 

namespace

UnityStandardAssets.ImageEffects 

{

[ExecuteInEditMode]

[RequireComponent
(typeof(Camera))]

public

class 
GrayEffect : PostEffectsBase 

{

public

Shader TintShader = null;

public

Color TintColour; 

public

Material TintMaterial = null;

public

override 
bool 
CheckResources () 

{

CheckSupport
(true);

TintMaterial
= CheckShaderAndCreateMaterial (TintShader,TintMaterial); 

if

(!isSupported) 

ReportAutoDisable
(); 

return

isSupported; 

}

public

void 
SetVector(Vector3 left,Vector3 right)

{

TintMaterial.SetVector
("_Line",new

Vector4(left.x,left.y,right.x,right.y));

}

public

void 
SetAB(float

a,float

b,float

hasA)

{

TintMaterial.SetVector
("_ab",new

Vector3(a,b,hasA));

}

void

OnRenderImage (RenderTexture source, RenderTexture destination) 

{

if

(CheckResources()==false)

{

Graphics.Blit
(source, destination); 

return;

}

TintMaterial.SetColor("TintColour",
TintColour); 

//Do
a full screen pass using TintMaterial 

Graphics.Blit
(source, destination, TintMaterial); 

}

}

}

Graphics.Blit 位塊傳送，拷貝源紋理到目的渲染紋理。可簡單理解爲獲取該相機的rendertexture作爲紋理，通過指定shader再渲染一遍
setvector函數用作將橫線上兩點座標傳入材質
setab即爲將y=ax+b形式的a,b傳入，並指明a是否有意義，因爲當直線形式爲x=某數字時，a無意義
具體計算如下

[C#] 純文本查看複製代碼

void

Calculate()

{

wpLeft
= portTrans.TransformPoint (new

Vector3 (-10f, 0f, 0f));//porttrans爲橫線中心trans

wpRight
= portTrans.TransformPoint (new

Vector3 (10f, 0f, 0f));

vpLeft
= mainCamera.WorldToViewportPoint (wpLeft);

vpRight
= mainCamera.WorldToViewportPoint (wpRight);

if

(vpLeft.x != vpRight.x) {

va
= (vpRight.y - vpLeft.y) / (vpRight.x - vpLeft.x);

vb
= vpLeft.y - vpLeft.x * va; 

wb
= wpLeft.y - wpLeft.x * va; 

hasA
= 1f;

}
else

{

va
= vb = hasA = 0f;

}

}

void

SetMaterial()

{

grayEffect.SetVector
(vpLeft, vpRight);

grayEffect.SetAB
(va,vb,hasA);

}

shader就是一個轉彩色爲灰度的shader，增加了判斷片原位於哪個區域的功能，判斷區域的代碼可以根據需求更改

[C#] 純文本查看複製代碼

Shader
"Custom/Tint"

{

Properties

{

_MainTex
("",
any) = ""

{} 

_Line
("line",
Vector) = (0,0,0,0)

_ab
("ab",
Vector) = (0,0,0)

}

CGINCLUDE

#include
"UnityCG.cginc" 

struct

v2f 

{

float4
pos : SV_POSITION; 

float3
wPos : TEXCOORD1;

float2
uv : TEXCOORD0; 

};

sampler2D
_MainTex; 

float4
_Line;

float3
_ab;

float4
TintColour; 

v2f
vert( appdata_img v ) 

{

v2f
o = (v2f)0; 

o.pos
= mul(UNITY_MATRIX_MVP, v.vertex); 

o.wPos
= v.vertex; 

o.uv
= v.texcoord; 

return

o; 

}

float4
frag(v2f input) : SV_Target 

{

float4
c = tex2D(_MainTex, input.uv); 

bool

isGray = false;

if(_ab.z==0)

{

if(_Line.y>_Line.w&&input.wPos.x>_Line.x)

{

isGray
= true;

}

if(_Line.y<_Line.w&&input.wPos.x<_Line.x)

{

isGray
= true;

}

}

else

{

float

ey = _ab.x*input.wPos.x + _ab.y;

if(_Line.x<_Line.z&&input.wPos.y>ey)

{

isGray
= true;

}

if(_Line.x>_Line.z&&input.wPos.y<ey)

{

isGray
= true;

}

}

if(isGray)

{

float

gray = dot(c.xyz, float3(0.299, 0.587, 0.114));

c.xyz
= float3(gray,gray,gray);

}

return

c; 

}

ENDCG

SubShader

{

Pass

{

ZTest
Always Cull Off ZWrite Off 

CGPROGRAM

#pragma
vertex vert 

#pragma
fragment frag 

ENDCG

}

}

Fallback
off 

}

dot(c.xyz, float3(0.299, 0.587, 0.114))就是把彩色信息轉化成灰度信息的數學公式，即爲x,y,z對應乘0.299 0.587,0.114

7.15更新：
感謝上蒼之冰提供的想法
優化了shader，去除了if語句

[C#] 純文本查看複製代碼

float4
c = tex2D(_MainTex, input.uv); 

float

ey = _ab.x*input.wPos.x + _ab.y;

bool

b1 = _Line.y>_Line.w&&input.wPos.x>_Line.x;

bool

b2 = _Line.y<_Line.w&&input.wPos.x<_Line.x;

bool

b3 = _Line.x<_Line.z&&input.wPos.y>ey;

bool

b4 = _Line.x>_Line.z&&input.wPos.y<ey;

bool

a1 = (_ab.z==0)&&(b1||b2);

bool

a2 = (_ab.z!=0)&&(b3||b4);

bool

d = a1||a2;

float

gray = dot(c.xyz, float3(0.299, 0.587, 0.114));

c.xyz
*= (!d);

c.xyz
+= float3(gray,gray,gray)*d;