//PixelShader
float4 RenderScenePS( VS_OUTPUT In ) :COLOR0
  { 
    // 计算视差贴图的偏移
    float3 ViewDir = normalize( In.vLookAt );
    float2 OffsetUV = In.TextureUV ;
    float3 h = tex2D( MeshHeightSampler ,In.TextureUV ).y ;
    OffsetUV += float2( -ViewDir.x , ViewDir.y ) * ( h * 0.04 - 0.02 );
    float4 texColor = tex2D( MeshTextureSampler ,OffsetUV );
    // 
    return texColor  ;
    
  }

VS_OUTPUT RenderSceneVS( VS_INPUT In )
  {
    
    VS_OUTPUT Out = ( VS_OUTPUT )0;
   //正常流程变化模型的顶点
    float4x4 matWorldView = mul( g_matWorld ,g_matView );
    float4x4 matWorldViewProject = mul( matWorldView ,g_matProject );
    Out.Position = mul( In.Position , matWorldViewProject );
    Out.TextureUV = In.TextureUV;
    //----------------- 在此计算一个变换矩阵 ---------------------
    // 将世界坐标变换到切线空间系的变换矩阵
    float3x3 matWorldToModel = float3x3 (
      mul( In.Tanget ,                   g_matWorld ).xyz ,
      mul( cross( In.Tanget,In.Normal ), g_matWorld ).xyz ,
      mul( In.Normal ,                   g_matWorld ).xyz );

    // 
    float4 Position = mul( In.Position ,g_matWorld );
    // 每个顶点上的指向观察者的方向
    Out.vLookAt = mul ( matWorldToModel ,normalize( Position - g_vEyePosition ));
    return Out;
  }

原理:

vec2 steepPallaxMapping(in vec3 v, in vec2 t)
{
	// determine number of layers from angle between V and N
	const float minLayers = 5;
	const float maxLayers = 15;
	float numLayers = mix(maxLayers, minLayers, abs(dot(vec3(0, 0, 1), v)));

	// height of each layer
	float layerHeight = 1.0 / numLayers;
	// depth of current layer
	float currentLayerHeight = 0;
	// shift of texture coordinates for each iteration
	vec2 dtex = gHeightScale * v.xy / v.z / numLayers;

 	// current texture coordinates
	vec2 currentTextureCoords = t;

	// get first depth from heightmap
 	float heightFromTexture = texture(NormTexSampler, currentTextureCoords).a;

	// while point is above surface
	while(heightFromTexture > currentLayerHeight) 
	{
		// to the next layer
		currentLayerHeight += layerHeight;
		// shift texture coordinates along vector V
		currentTextureCoords -= dtex;
		// get new depth from heightmap
		heightFromTexture = texture(NormTexSampler, currentTextureCoords).a;
   }

   return currentTextureCoords;
}