Blend 2 Textures by Lightmap Alpha

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Author: Jessy

Description

A textured quad that uses this shader.

This shader mixes two tiling textures based on an alpha blending map, and uses a lightmap instead of real-time lighting.

Usage

In your modeling app, you create two UV sets - one for Texture 1 and Texture 2, and another for the lightmap and blending map. The idea is that you will tile the textures using UV1, but not in UV2 - standard lightmapping practice. By default, this means that your two main textures will tile at the same "rate", but you can use the Offset and/or Tiling controls in the Material, if you think it will add visual interest.

The blend map is stored in the alpha channel of the lightmap. The two textures mix as if, in Photoshop, you had Texture 1 in a layer above Texture 2, and Texture 1 used the blend map as a layer mask. i.e. white = Texture 1, black = Texture 2. In my usage so far, I've found that it's important to have the lightmap/splatmap be at a high resolution, to preserve the shape of fine splat details, but that it's okay to use PVRTC 2 bpp compression, as the color detail is mainly coming from Texture 1 and Texture 2.

ShaderLab - Blend 2 Textures by Lightmap Alpha.shader

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Shader "Blend 2 Textures by Lightmap Alpha" {

Properties {
	_MainTex ("Texture 1 (RGB)", 2D) = ""
	_Tex2 ("Texture 2 (RGB)", 2D) = ""
	_Lightmap ("Lightmap (A=Blend)", 2D) = ""
}

// iPhone 3GS and later
SubShader {Pass {
	GLSLPROGRAM
	varying mediump vec2 mainTexUV, tex2UV, lightmapUV;
			
	#ifdef VERTEX		
	uniform mediump vec4 _MainTex_ST, _Tex2_ST;
	void main() {
		gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
		mainTexUV = gl_MultiTexCoord0.xy * _MainTex_ST.xy + _MainTex_ST.zw;
		tex2UV = gl_MultiTexCoord0.xy * _Tex2_ST.xy + _Tex2_ST.zw;
		lightmapUV = gl_MultiTexCoord1.xy;		
	}
	#endif
	
	#ifdef FRAGMENT
	uniform lowp sampler2D _MainTex, _Tex2, _Lightmap;
	void main() {
		lowp vec4 lightmap_mix = texture2D(_Lightmap, lightmapUV);
		gl_FragColor = lightmap_mix *
			mix(texture2D(_Tex2, tex2UV), texture2D(_MainTex, mainTexUV), lightmap_mix.a);
	}
	#endif  
	ENDGLSL
}}

// pre-3GS devices, including the September 2009 8GB iPod touch
SubShader {
	BindChannels {
		Bind "vertex", vertex
		Bind "texcoord", texcoord0	// 1st UV - tiling textures		
		Bind "texcoord1", texcoord1	// 2nd UV - lightmap and blend map
	}
	Pass {			
		SetTexture[_Tex2]
		SetTexture[_Lightmap] {Combine previous * texture}
	}
	Pass {
		Blend SrcAlpha OneMinusSrcAlpha	
		SetTexture[_MainTex]
		// Apply the lightmap to Texture 1 
		// and blend in the result, using the alpha map
		SetTexture[_Lightmap] {Combine previous * texture, texture}
	}
}
 
}
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