涂抹还是满常见的效果。
要做涂抹，首先要存一张中间贴图作为mask。
然后需要两个shader，一个做mask一个做混合。
MaskShader:
Shader "Unlit/MaskShader"{ Properties { _MainTex ("Texture", 2D) = "white" {} _MaskDecalTex("Mask Decal Texture", 2D) = "white" {} _MaskOffset("Mask Offset", vector) = (0,0,0,0) } SubShader { Tags { "RenderType"="Opaque" } LOD 100 Pass { CGPROGRAM #pragma vertex vert #pragma fragment frag // make fog work #pragma multi_compile_fog #include "UnityCG.cginc" struct appdata { float4 vertex : POSITION; float2 uv : TEXCOORD0; }; struct v2f { float2 uv : TEXCOORD0; float4 vertex : SV_POSITION; }; sampler2D _MainTex; float4 _MainTex_ST; float4 _MaskOffset; sampler2D _MaskDecalTex; v2f vert (appdata v) { v2f o; o.vertex = UnityObjectToClipPos(v.vertex); o.uv = TRANSFORM_TEX(v.uv, _MainTex); return o; } fixed4 frag (v2f i) : SV_Target { fixed4 r = tex2D(_MainTex, i.uv);#if UNITY_UV_STARTS_AT_TOP float grabSign = -_ProjectionParams.x;#else float grabSign = _ProjectionParams.x;#endif half2 uv = float2(1, grabSign) * (i.uv - half2(0.5, 0.5)) / _MaskOffset.ww + half2(0.5, 0.5); fixed4 mask = tex2D(_MaskDecalTex, uv + _MaskOffset.xy); return r + mask; } ENDCG } }}
BlendShader:
Shader "Unlit/BlendShader"{ Properties { _MainTex ("Texture", 2D) = "white" {} _SecondTex("Second Texture", 2D) = "white" {} _MaskTex("Mask Texture", 2D) = "white" {} } SubShader { Tags { "RenderType"="Opaque" } LOD 100 Pass { CGPROGRAM #pragma vertex vert #pragma fragment frag // make fog work #pragma multi_compile_fog #include "UnityCG.cginc" struct appdata { float4 vertex : POSITION; float2 uv : TEXCOORD0; }; struct v2f { float2 uv : TEXCOORD0; float4 vertex : SV_POSITION; }; sampler2D _MainTex; float4 _MainTex_ST; sampler2D _SecondTex; sampler2D _MaskTex; v2f vert (appdata v) { v2f o; o.vertex = UnityObjectToClipPos(v.vertex); o.uv = TRANSFORM_TEX(v.uv, _MainTex); return o; } fixed4 frag (v2f i) : SV_Target { fixed4 col1 = tex2D(_MainTex, i.uv); fixed4 col2 = tex2D(_SecondTex, i.uv);#if UNITY_UV_STARTS_AT_TOP float grabSign = -_ProjectionParams.x;#else float grabSign = _ProjectionParams.x;#endif half2 uv = float2(1, grabSign) * (i.uv - half2(0.5, 0.5)) + half2(0.5, 0.5); fixed4 mask = tex2D(_MaskTex, uv); return lerp(col1, col2, mask.a); } ENDCG } }}
脚本(核心部分)：
Vector4 viewPortPoint = Camera.main.WorldToViewportPoint(maskMappingPoint.position);viewPortPoint -= new Vector4(0.5f, 0.5f);viewPortPoint.w = maskMappingPoint.localScale.x;if (mPersistMaskTex == null){ mPersistMaskTex = new Texture2D(src.width, src.height, TextureFormat.RGBA32, false, true); for (int x = 0; x < mPersistMaskTex.width; x++) for (int y = 0; y < mPersistMaskTex.height; y++) mPersistMaskTex.SetPixel(x, y, new Color(0, 0, 0, 0)); mPersistMaskTex.Apply();}maskMat.SetTexture("_MainTex", mPersistMaskTex);maskMat.SetVector("_MaskOffset", viewPortPoint);Graphics.Blit(mPersistMaskTex, maskRT, maskMat);blendMat.SetTexture("_MainTex", src);blendMat.SetTexture("_SecondTex", tempRT);blendMat.SetTexture("_MaskTex", maskRT);Graphics.Blit(src, des, blendMat);var cacheActive = RenderTexture.active;RenderTexture.active = maskRT;mPersistMaskTex.ReadPixels(new Rect(0, 0, mPersistMaskTex.width, mPersistMaskTex.height), 0, 0);mPersistMaskTex.Apply();RenderTexture.active = cacheActive;
2018/11/18补充：近期实现了对涂抹像素的判断操作，涂抹到一定程度后则完成擦除：