opengl 渲染法线图

根据提供的引用内容，我们可以使用几何着色器来渲染法线图。具体步骤如下：

1.在顶点着色器中计算每个顶点的法线向量，并将其传递给几何着色器。

#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec3 aNormal;

out vec3 Normal;

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

void main()
{
    gl_Position = projection * view * model * vec4(aPos, 1.0);
    Normal = mat3(transpose(inverse(model))) * aNormal;
}

2.在几何着色器中，将每个顶点的位置和法线向量传递给片段着色器，并计算出每个顶点的切线和副切线向量。

#version 330 core
layout (triangles) in;
layout (line_strip, max_vertices = 6) out;

in vec3 Normal[];

out vec3 FragPos;
out vec3 NormalVec;
out vec2 TexCoords;

void main()
{
    for(int i = 0; i < 3; i++)
    {
        FragPos = gl_in[i].gl_Position.xyz;
        NormalVec = normalize(Normal[i]);

        // 计算切线和副切线向量
        vec3 tangent = normalize(vec3(model * vec4(1.0, 0.0, 0.0, 0.0)));
        vec3 bitangent = cross(NormalVec, tangent);
        vec3 T = normalize(vec3(model * vec4(tangent, 0.0)));
        vec3 B = normalize(vec3(model * vec4(bitangent, 0.0)));

        gl_Position = gl_in[i].gl_Position;
        TexCoords = vec2(0.0, 0.0);
        EmitVertex();

        gl_Position = gl_in[i].gl_Position + vec4(T, 0.0) * 0.1;
        TexCoords = vec2(1.0, 0.0);
        EmitVertex();

        gl_Position = gl_in[i].gl_Position;
        TexCoords = vec2(0.0, 0.0);
        EmitVertex();

        gl_Position = gl_in[i].gl_Position + vec4(B, 0.0) * 0.1;
        TexCoords = vec2(0.0, 1.0);
        EmitVertex();

        gl_Position = gl_in[i].gl_Position;
        TexCoords = vec2(0.0, 0.0);
        EmitVertex();

        gl_Position = gl_in[i].gl_Position + vec4(NormalVec, 0.0) * 0.1;
        TexCoords = vec2(1.0, 1.0);
        EmitVertex();

        EndPrimitive();
    }
}

3.在片段着色器中，将法线向量转换为颜色值，并输出到屏幕上。

#version 330 core
out vec4 FragColor;

in vec3 FragPos;
in vec3 NormalVec;
in vec2 TexCoords;

uniform sampler2D texture_diffuse1;

void main()
{
    vec3 color = (NormalVec + vec3(1.0)) * 0.5;
    FragColor = vec4(color, 1.0);
}

4.为点的顶点数据生成一个VAO和一个VBO，然后使用glDrawArrays进行绘制。

shader.use()
glBindVertexArray(VAO)
glDrawArrays(GL_TRIANGLES, 0, 36)