Spine无需光照的阴影实现

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阴影生成的实现方式

1.实时光照
2.脚底放置假的阴影面片模拟阴影
3.变幻模型在某个平面上投影形成2d压缩模型
4.project投影器

具体做法

这里我们使用方案3方案实现，因为spine是2d的投影替换为使用旋转和切变来实现。具体实现通过两个pass，第一个pass做模型的变换处理，生成一个阴影；第二个pass使用默认的渲染画出本身的模型。

github工程连接：https://github.com/xulinjia/spine_shadow
shader代码如下：
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Shader "Spine/SkeletonShadow" {
	Properties {
		_ShadowColor("ShadowColor",Color) = (0,0,0,0.5)	//阴影颜色
		_ShadowDdge("ShadowDege",range(0,1.507)) = 0		//绕x轴的旋转角度
		_ShadowCutD("_ShadowCutD",float) = 0.5				//切变距离
		_ShadowHeightScale("_ShadowHeight",float) = 1		// 影子高度比例
		_Cutoff ("Shadow alpha cutoff", Range(0,1)) = 0.1
		[NoScaleOffset] _MainTex ("Main Texture", 2D) = "black" {}
		[Toggle(_STRAIGHT_ALPHA_INPUT)] _StraightAlphaInput("Straight Alpha Texture", Int) = 0
		[HideInInspector] _StencilRef("Stencil Reference", Float) = 1.0
		[HideInInspector][Enum(UnityEngine.Rendering.CompareFunction)] _StencilComp("Stencil Comparison", Float) = 8 // Set to Always as default

		// Outline properties are drawn via custom editor.
		[HideInInspector] _OutlineWidth("Outline Width", Range(0,8)) = 3.0
		[HideInInspector] _OutlineColor("Outline Color", Color) = (1,1,0,1)
		[HideInInspector] _OutlineReferenceTexWidth("Reference Texture Width", Int) = 1024
		[HideInInspector] _ThresholdEnd("Outline Threshold", Range(0,1)) = 0.25
		[HideInInspector] _OutlineSmoothness("Outline Smoothness", Range(0,1)) = 1.0
		[HideInInspector][MaterialToggle(_USE8NEIGHBOURHOOD_ON)] _Use8Neighbourhood("Sample 8 Neighbours", Float) = 1
		[HideInInspector] _OutlineOpaqueAlpha("Opaque Alpha", Range(0,1)) = 1.0
		[HideInInspector] _OutlineMipLevel("Outline Mip Level", Range(0,3)) = 0
	}

	SubShader {
		Tags { "Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Transparent" "PreviewType"="Plane" }

		Fog { Mode Off }
		Cull Off
		ZWrite Off
		Blend One OneMinusSrcAlpha
		Lighting Off

		Stencil {
			Ref[_StencilRef]
			Comp[_StencilComp]
			Pass Keep
		}

		Pass {
			Name "FastShadow"
			Blend SrcAlpha Zero
			CGPROGRAM
			#pragma shader_feature _ _STRAIGHT_ALPHA_INPUT
			#pragma vertex vert
			#pragma fragment frag
			#include "UnityCG.cginc"
			#include "CGIncludes/Spine-Common.cginc"
			sampler2D _MainTex;
			fixed _Cutoff;
			float4 _ShadowColor;
			float _ShadowDdge;
			float _ShadowCutD;
			float _ShadowHeightScale;

			struct VertexInput {
				float4 vertex : POSITION;
				float2 uv : TEXCOORD0;
				float4 vertexColor : COLOR;
			};

			struct VertexOutput {
				float4 pos : SV_POSITION;
				float2 uv : TEXCOORD0;
				float4 vertexColor : COLOR;
			};

			VertexOutput vert (VertexInput v) {
				VertexOutput o;
				float4 vt = v.vertex;
				float4 vtn;
				vt.y *= _ShadowHeightScale;
				vtn.x = vt.x + vt.y * _ShadowCutD;
				vtn.y = cos(_ShadowDdge) * vt.y;
				vtn.z = sin(_ShadowDdge) * vt.y;
				vtn.w = vt.w;
				o.pos = UnityObjectToClipPos(vtn);
				o.uv = v.uv;
				o.vertexColor = PMAGammaToTargetSpace(v.vertexColor);
				return o;
			}

			float4 frag (VertexOutput i) : SV_Target {
				float4 texColor = tex2D(_MainTex, i.uv);

				#if defined(_STRAIGHT_ALPHA_INPUT)
				texColor.rgb *= texColor.a;
				#endif
				float4 shadowColor = _ShadowColor;
				clip(texColor.a * i.vertexColor.a - 0.01);
				return shadowColor;

			}
			ENDCG
		}


		Pass {
			Name "Normal"

			CGPROGRAM
			#pragma shader_feature _ _STRAIGHT_ALPHA_INPUT
			#pragma vertex vert
			#pragma fragment frag
			#include "UnityCG.cginc"
			#include "CGIncludes/Spine-Common.cginc"
			sampler2D _MainTex;

			struct VertexInput {
				float4 vertex : POSITION;
				float2 uv : TEXCOORD0;
				float4 vertexColor : COLOR;
			};

			struct VertexOutput {
				float4 pos : SV_POSITION;
				float2 uv : TEXCOORD0;
				float4 vertexColor : COLOR;
			};

			VertexOutput vert (VertexInput v) {
				VertexOutput o;
				o.pos = UnityObjectToClipPos(v.vertex);
				o.uv = v.uv;
				o.vertexColor = PMAGammaToTargetSpace(v.vertexColor);
				return o;
			}

			float4 frag (VertexOutput i) : SV_Target {
				float4 texColor = tex2D(_MainTex, i.uv);

				#if defined(_STRAIGHT_ALPHA_INPUT)
				texColor.rgb *= texColor.a;
				#endif

				return (texColor * i.vertexColor);
			}
			ENDCG
		}

		Pass {
			Name "Caster"
			Tags { "LightMode"="ShadowCaster" }
			Offset 1, 1
			ZWrite On
			ZTest LEqual

			Fog { Mode Off }
			Cull Off
			Lighting Off

			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#pragma multi_compile_shadowcaster
			#pragma fragmentoption ARB_precision_hint_fastest
			#include "UnityCG.cginc"
			sampler2D _MainTex;
			fixed _Cutoff;

			struct VertexOutput {
				V2F_SHADOW_CASTER;
				float4 uvAndAlpha : TEXCOORD1;
			};

			VertexOutput vert (appdata_base v, float4 vertexColor : COLOR) {
				VertexOutput o;
				o.uvAndAlpha = v.texcoord;
				o.uvAndAlpha.a = vertexColor.a;
				TRANSFER_SHADOW_CASTER(o)
				return o;
			}

			float4 frag (VertexOutput i) : SV_Target {
				fixed4 texcol = tex2D(_MainTex, i.uvAndAlpha.xy);
				clip(texcol.a * i.uvAndAlpha.a - _Cutoff);
				SHADOW_CASTER_FRAGMENT(i)
			}
			ENDCG
		}
	}
	CustomEditor "SpineShaderWithOutlineGUI"
}