c – 法线贴图：与碎片着色器相比,顶点着色器中的TBN矩阵不同

我正在研究教程的常规映射实现,为了教学目的,我想将TBN矩阵传递给片段着色器(来自顶点着色器),这样我就可以将切线空间中的法向量转换为世界空间用于照明计算.法线贴图应用于2D平面,其法线指向正z方向.

但是,当我在平面的顶点着色器中计算TBN矩阵时(因此所有顶点的所有切线/位数都相同),显示的法线完全关闭.如果我将切线/比特和法线向量传递给片段着色器并在那里构建TBN,它可以正常工作,如下图所示(显示法线)：

这是它变得奇怪的地方.因为平面是平坦的,所以它的所有顶点的T,B和N矢量都是相同的,因此TBN矩阵对于每个片段也应该是相同的(因为片段插值不会改变任何东西).顶点着色器中的TBN矩阵应与片段着色器中的TBN矩阵完全相同,但视觉输出则另有说明.

顶点和片段着色器的源代码如下：

顶点：

#version 330 core
layout (location = 0) in vec3 position;
layout (location = 1) in vec3 normal;
layout (location = 2) in vec2 texCoords;
layout (location = 3) in vec3 tangent;
layout (location = 4) in vec3 bitangent;

out VS_OUT {
    vec3 FragPos;
    vec3 Normal;
    vec2 TexCoords;
    vec3 Tangent;
    vec3 Bitangent;
    mat3 TBN;
} vs_out;

uniform mat4 projection;
uniform mat4 view;
uniform mat4 model;

void main()
{
    gl_Position = projection * view * model * vec4(position,1.0f);
    vs_out.FragPos = vec3(model * vec4(position,1.0));   
    vs_out.TexCoords = texCoords;

    mat3 normalMatrix = transpose(inverse(mat3(model)));
    vs_out.Normal = normalize(normalMatrix * normal);

    vec3 T = normalize(normalMatrix * tangent);
    vec3 B = normalize(normalMatrix * bitangent);
    vec3 N = normalize(normalMatrix * normal);
    vs_out.TBN = mat3(T,B,N);

    vs_out.Tangent = T;
    vs_out.Bitangent = B;
}

分段

#version 330 core
out vec4 FragColor;

in VS_OUT {
    vec3 FragPos;
    vec3 Normal;
    vec2 TexCoords;
    vec3 Tangent;
    vec3 Bitangent;
    mat3 TBN;
} fs_in;

uniform sampler2D diffuseMap;
uniform sampler2D normalMap;

uniform vec3 lightPos;
uniform vec3 viewPos;

uniform bool normalMapping;

void main()
{           
    vec3 normal = fs_in.Normal;
    mat3 tbn;
    if(normalMapping)
    {
        // Obtain normal from normal map in range [0,1]
        normal = texture(normalMap,fs_in.TexCoords).rgb;
        // Transform normal vector to range [-1,1]
        normal = normalize(normal * 2.0 - 1.0);   
        // Then transform normal in tangent space to world-space via TBN matrix
        tbn = mat3(fs_in.Tangent,fs_in.Bitangent,fs_in.Normal); // TBN calculated in fragment shader
        // normal = normalize(tbn * normal); // This works!
        normal = normalize(fs_in.TBN * normal); // This gives incorrect results
    }

    // Get diffuse color
    vec3 color = texture(diffuseMap,fs_in.TexCoords).rgb;
    // Ambient
    vec3 ambient = 0.1 * color;
    // Diffuse
    vec3 lightDir = normalize(lightPos - fs_in.FragPos);
    float diff = max(dot(lightDir,normal),0.0);
    vec3 diffuse = diff * color;
    // Specular
    vec3 viewDir = normalize(viewPos - fs_in.FragPos);
    vec3 reflectDir = reflect(-lightDir,normal);
    vec3 halfwayDir = normalize(lightDir + viewDir);  
    float spec = pow(max(dot(normal,halfwayDir),0.0),32.0);

    vec3 specular = vec3(0.2) * spec; // assuming bright white light color
    FragColor = vec4(ambient + diffuse + specular,1.0f);
    FragColor = vec4(normal,1.0); // display normals for debugging
}

两个TBN矩阵都明显不同.下面我编译了不同片段着色器输出的图像：

您可以看到T,B和N向量是正确的,片段着色器的tbn矩阵也是正确的,但顶点着色器fs_in.TBN中的TBN矩阵给出了完全虚假的值.

我完全不知道为什么它不起作用.我知道我可以简单地将Tangent和Bitangent向量传递给片段着色器,在那里计算它并完成它但我很好奇为什么这不起作用的确切原因？