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第13章 顶点着色器的妙用/Sample13_3/assets/frag_landform.sh

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+precision mediump float;
+varying vec2 vTextureCoord; //接收纹理坐标参数
+varying float vertexHeight;//接受顶点的高度值
+uniform sampler2D sTextureSand;//纹理内容数据   ----沙滩
+uniform sampler2D sTextureGrass;//纹理内容数据-----草地
+void main()                         
+{       
+	float height1=15.0;  
+	float height2=25.0;    
+   vec4 finalSand=texture2D(sTextureSand, vTextureCoord);//沙滩
+   vec4 finalGrass=texture2D(sTextureGrass, vTextureCoord);   //草地
+   if(vertexHeight<height1)//绘制沙滩
+   {
+  	  gl_FragColor = finalSand;
+   }
+   else if(vertexHeight<height2)//绘制草地和沙滩混合层
+   {
+      float ratio=(vertexHeight-height1)/(height2-height1);	
+      finalSand *=(1.0-ratio); 
+   	  finalGrass *=ratio;
+      gl_FragColor =finalGrass+ finalSand;
+   }
+   else//绘制草地
+   {
+      gl_FragColor = finalGrass;
+   }
+}