如何解决法线贴图覆盖 DirectX 11 中的平滑边缘
我的对象是一个光滑的桶,只有颜色和原始法线看起来像这样:
当我尝试通过纹理添加法线细节时,平滑法线会像这样被覆盖:
有没有更好的方法来合并新的法线纹理而不覆盖平滑的边缘?
代码主要来自此处的 rastertek 教程https://www.rastertek.com/tutdx11.html
顶点着色器
cbuffer MatrixBuffer
{
matrix worldMatrix;
matrix viewMatrix;
matrix projectionMatrix;
};
struct VertexInputType
{
float4 position : POSITION;
float2 tex : TEXCOORD0;
float3 normal : norMAL;
float3 tangent : TANGENT;
float3 binormal : BInorMAL;
};
struct PixelInputType
{
float4 position : SV_POSITION;
float2 tex : TEXCOORD0;
float3 normal : norMAL;
float3 tangent : TANGENT;
float3 binormal : BInorMAL;
};
PixelInputType normalMapVertexShader(VertexInputType input)
{
PixelInputType output;
// Change the position vector to be 4 units for proper matrix calculations.
input.position.w = 1.0f;
// Calculate the position of the vertex against the world,view,and projection matrices.
output.position = mul(input.position,worldMatrix);
output.position = mul(output.position,viewMatrix);
output.position = mul(output.position,projectionMatrix);
// Store the texture coordinates for the pixel shader.
output.tex = input.tex;
// Calculate the normal vector against the world matrix only and then normalize the final value.
output.normal = mul(input.normal,(float3x3)worldMatrix);
output.normal = normalize(output.normal);
// Calculate the tangent vector against the world matrix only and then normalize the final value.
output.tangent = mul(input.tangent,(float3x3)worldMatrix);
output.tangent = normalize(output.tangent);
// Calculate the binormal vector against the world matrix only and then normalize the final value.
output.binormal = mul(input.binormal,(float3x3)worldMatrix);
output.binormal = cross(output.tangent,output.normal);
return output;
}
像素着色器
Texture2D shaderTextures[2];
SamplerState SampleType;
cbuffer LightBuffer
{
float4 diffuseColor;
float3 lightDirection;
};
struct PixelInputType
{
float4 position : SV_POSITION;
float2 tex : TEXCOORD0;
float3 normal : norMAL;
float3 tangent : TANGENT;
float3 binormal : BInorMAL;
};
float4 normalMapPixelShader(PixelInputType input) : SV_TARGET
{
float4 textureColor;
float4 bumpMap;
float3 bumpnormal;
float3 lightDir;
float lightIntensity;
float4 color;
// Sample the texture pixel at this location.
textureColor = shaderTextures[0].Sample(SampleType,input.tex);
// Sample the pixel in the bump map.
bumpMap = shaderTextures[1].Sample(SampleType,input.tex);
// Expand the range of the normal value from (0,+1) to (-1,+1).
bumpMap = (bumpMap * 2.0f) - 1.0f;
// Calculate the normal from the data in the bump map.
bumpnormal = (bumpMap.x * input.tangent) + (bumpMap.y * input.binormal) + (bumpMap.z * input.normal);
// normalize the resulting bump normal.
bumpnormal = normalize(bumpnormal);
// Invert the light direction for calculations.
lightDir = -lightDirection;
// Calculate the amount of light on this pixel based on the bump map normal value.
lightIntensity = saturate(dot(bumpnormal,lightDir));
// Determine the final diffuse color based on the diffuse color and the amount of light intensity.
color = saturate(diffuseColor * lightIntensity);
// Combine the final bump light color with the texture color.
color = color * textureColor;
return color;
}
解决方法
问题在于这个公式:
// Calculate the normal from the data in the bump map.
bumpNormal = (bumpMap.x * input.tangent) + (bumpMap.y * input.binormal) + (bumpMap.z * input.normal);
更好的方法是为局部切线空间创建一个矩阵,然后从纹理转换局部法线。
// Given a local normal,transform it into a tangent space given by surface normal and tangent
float3 PeturbNormal(float3 localNormal,float3 surfaceNormalWS,float3 surfaceTangentWS)
{
float3 normal = normalize(surfaceNormalWS);
float3 tangent = normalize(surfaceTangentWS);
float3 binormal = cross(normal,tangent); // reconstructed from normal & tangent
float3x3 TBN = { tangent,binormal,normal }; // world "frame" for local normal
return mul(localNormal,TBN); // transform to local to world (tangent space)
}
// This function converts the R and G channels from a normal texture map
// Assumes the input data is "UNORM" (i.e. needs a x2 bias to get back -1..1)
// Also reconstructs the B channel in case the normal map was compressed as BC5_UNORM
float3 TwoChannelNormalX2(float2 normal)
{
float2 xy = 2.0f * normal - 1.0f;
float z = sqrt(1 - dot(xy,xy));
return float3(xy.x,xy.y,z);
}
...
// Before lighting,peturb the surface's normal by the one given in normal map.
float3 localNormal = TwoChannelNormalX2(NormalTexture.Sample(Sampler,pin.TexCoord).xy);
float3 N = PeturbNormal( localNormal,pin.NormalWS,pin.TangentWS);
取自 DirectX Tool Kit 的 NormalMap
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