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第11章 常用3D开发技巧案例/Sample11_6/assets/frag_mountion.sh

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+precision mediump float;
+varying vec2 vTextureCoord; //接收从顶点着色器过来的参数
+uniform sampler2D sTexture;//纹理内容数据
+varying float currY;
+uniform sampler2D sTextureGrass;//纹理内容数据（草皮）
+uniform sampler2D sTextureRock;//纹理内容数据（岩石）
+uniform float landStartY;//陆地起始Y
+uniform float landYSpan;//陆地Y偏移量
+
+void main()
+{           
+   	   float min=0.25;
+	   float max=0.7;
+	   
+	   float currYRatio=(currY-landStartY)/landYSpan;
+	   
+	   vec4 gColor=texture2D(sTextureGrass, vTextureCoord); 
+	   vec4 rColor=texture2D(sTextureRock, vTextureCoord); 
+	   
+	   vec4 finalColor;
+	   
+	   if(currYRatio<min)
+	   {
+	      finalColor=gColor;
+	   }
+	   else if(currYRatio>max)
+	   {
+	      finalColor=rColor;
+	   }
+	   else
+	   {
+	      float rockBL=(currYRatio-min)/(max-min);
+	      finalColor=rockBL*rColor+(1.0-rockBL)*gColor;
+	   }
+	   //给此片元从纹理中采样出颜色值            
+	   gl_FragColor = finalColor; 
+}