Unity Shader 实现刮刮乐效果

发表于2018-11-20
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网上关于实现刮刮乐的文章有很多,可以使用UGUI实现刮刮乐效果,也可以使用shader来实现,本篇中给大家分享的是第二种,利用Shader实现刮刮乐效果。


实现思路:

1.当按下鼠标时,我们就克隆一个笔刷,这样就形成了涂画的效果。

2.然后我们写一个遮罩shader,shader中需要两张图,一张是遮罩的图片(,另一张是用于剔除遮罩的图片,我们将渲染出的rendertexture作为剔除遮罩的图片。这样就完成了刮刮乐效果。

实现代码

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;

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