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// Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'
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// Upgrade NOTE: replaced '_World2Object' with 'unity_WorldToObject'
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Shader "Unity Shaders Book/Chapter 11/Billboard"
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{
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Properties
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{
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_MainTex("Main Tex", 2D) = "white" {}
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_Color("Color Tint", Color) = (1,1,1,1)
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//调整时是固定法线还是固定指向上的方向，即约束垂直方向的程度
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_VerticalBillboarding("Vertical Restraints", Range(0,1)) = 1
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}
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SubShader
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{
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//由于序列帧图像通常是透明背景，所以需要设置pass的相关状态，以渲染透明效果
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//半透明“标配”,DisableBatching指明是否对该SubShader使用批处理，批处理会合并所有相关模型，模型各自的模型空间就会丢失
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//广告牌技术需要使用物体的模型空间下的位置来作为锚点进行计算
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Tags{ "Queue" = "Transparent" "IgnoreProject" = "True" "RenderType" = "Transparent" "DisableBatching" = "True" }
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Pass
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{
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Tags{ "LightMode" = "ForwardBase" }
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//为了让广告牌的每个面都能显示
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//关闭深度写入
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ZWrite off
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//开启并设置混合模式
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Blend SrcAlpha OneMinusSrcAlpha
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//关闭剔除功能
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Cull Off
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CGPROGRAM
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#pragma vertex vert
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#pragma fragment frag
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#include "UnityCG.cginc"
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sampler2D _MainTex;
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float4 _MainTex_ST;
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fixed4 _Color;
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float _VerticalBillboarding;
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struct a2v
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{
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float4 vertex : POSITION;
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float4 texcoord : TEXCOORD0;
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};
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struct v2f
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{
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float4 pos : SV_POSITION;
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float2 uv : TEXCOORD0;
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};
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v2f vert(a2v v)
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{
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v2f o;
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//选择模型空间的原点作为广告牌的锚点
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float3 center = float3(0, 0, 0);
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//获取模型空间下的视角位置
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float3 viewer = mul(unity_WorldToObject, float4(_WorldSpaceCameraPos, 1));
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//开始计算3个正交矢量
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//根据观察方向和锚点计算目标法线方向
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float3 normalDir = viewer - center;
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//根据_VerticalBillboarding属性控制垂直方向上的约束
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//当_VerticalBillboarding为1时，法线方向固定，为视角方向；
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//当_VerticalBillboarding为0时，向上方向固定，为(0,1,0)
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//获得的法线方向需要进行归一化操作得到单位矢量
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normalDir.y = normalDir.y * _VerticalBillboarding;
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normalDir = normalize(normalDir);
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//获得粗略的向上方向，为了方式法线方向和向上方向平行(如果平行，叉积会得到错误的结果)，对法线方向的y分量进行判断
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float3 upDir = abs(normalDir.y) > 0.999 ? float3(0, 0, 1) : float3(0, 1, 0);
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//根据法线方向和粗略的向上方向得到向右方向，并归一化
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float3 rightDir = normalize(cross(upDir, normalDir));
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//根据法线方向和向右方向获得准确的向上方向
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upDir = normalize(cross(normalDir, rightDir));
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//根据原始的位置相对于锚点的偏移量以及3个正交基矢量，以计算得到新的顶点位置
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float3 centerOffs = v.vertex.xyz - center;
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float3 localPos = center + rightDir * centerOffs.x + upDir * centerOffs.y + normalDir * centerOffs.z;
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//把模型空间的顶点位置变换到裁剪空间
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o.pos = UnityObjectToClipPos(float4(localPos, 1));
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o.uv = TRANSFORM_TEX(v.texcoord, _MainTex);
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return o;
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}
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fixed4 frag(v2f i) : SV_Target
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{
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//对纹理进行采样
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fixed4 c = tex2D(_MainTex,i.uv);
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//混合颜色
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c.rgb *= _Color.rgb;
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return c;
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}
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ENDCG
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}
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}
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Fallback"Transparent/VertexLit"
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}
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