OpenGL：在着色器中实现的 Blinn-Phong 模型给出错误的结果

Question

首先，我是计算机图形学、openGL 的新手，并且具备 C++ 编码的基本知识。我已经为 openGL 项目苦苦挣扎了一个月，已经到了必须使用 Blinn-Phong 模型实现着色的地步。我已经在顶点和片段着色器中实现了计算。代码中可能存在一些小错误，因为没有着色一切都可以完美运行，但是在将着色部分添加到着色器之后，任何事情都不会发生。我在片段着色器中计算表面法线，并使用纹理而不仅仅是颜色。我还为每个对象（总共 7 个对象）使用自己的着色器。

如果有人马上看到我做错了什么，我会非常高兴。我不再收到错误，所以错误可能在实施中。

这是一个对象顶点和片段着色器的代码。

顶点着色器：

#version 330 core
layout (location=0) in vec3 in_Position;
layout (location=3) in vec2 in_TexCoord0;

// mvpmatrix is the result of multiplying the model, view, and projection matrices
uniform mat4 mvpmatrix;

// Texture coordinate for the fragment shader
out vec2 f_TexCoord0;
out vec3 out_Position;

void main(void)
{
    gl_Position = mvpmatrix * vec4(in_Position, 1.0);
    out_Position = in_Position;

    f_TexCoord0 = in_TexCoord0;
}

片段着色器：

#version 330 core
uniform sampler2D texture1;
in vec2 f_TexCoord0;
in vec3 out_Position;
layout (location=0) out vec4 fragColor;

uniform vec4 ambientMaterial2, diffuseMaterial2, specularMaterial2;
uniform vec4 ambientLight, diffuseLight, specularLight;
uniform mat4 viewMatrix;
uniform mat4 projectionMatrix;
uniform vec4 lightPosition;
uniform float shininess;

void main(void)
{
    vec4 ambientProduct = ambientLight * ambientMaterial2;
    vec4 diffuseProduct = diffuseLight * diffuseMaterial2;
    vec4 specularProduct = specularLight * specularMaterial2;

    vec3 pos = out_Position.xyz;
    vec3 nv = cross(dFdx(pos),dFdy(pos));
    nv = nv * sign(nv.z);
    vec3 L = normalize(lightPosition.xyz - nv);
    vec3 E = normalize(-nv); 
    vec3 H = normalize(L + E);
    vec3 N = nv;

    float Kd = max(dot(L, N), 0.0);
    vec4 diffuse = Kd * diffuseProduct;

    vec4 specular = vec4(0.0, 0.0, 0.0, 1.0);
    if (Kd > 0.0f)
    {
        float Ks = dot(H, N);
        if (Ks > 0.0f)
            {
            specular = pow(Ks, shininess) * specularProduct;
            }
    }
    vec4 fragColor_lightning = (ambientProduct + diffuse + specular);
    vec4 fragColor_texture = texture2D(texture1, vec2(f_TexCoord0.x, f_TexCoord0.y));
    fragColor = fragColor_lightning + fragColor_texture;
}

---

编辑：

更改的着色器：

顶点着色器：

#version 330 core
layout (location=0) in vec3 in_Position;
layout (location=3) in vec2 in_TexCoord0;

// mvpmatrix is the result of multiplying the model, view, and projection matrices
uniform mat4 mvpmatrix;
uniform mat4 modelMat;

// Texture coordinate for the fragment shader
out vec2 f_TexCoord0;
out vec3 viewPos;

void main(void)
{
    gl_Position = mvpmatrix * vec4(in_Position, 1.0);
    viewPos = (modelMat * vec4(in_Position, 1.0)).xyz;
    f_TexCoord0 = in_TexCoord0;
}

片段着色器：

#version 330 core
uniform sampler2D texture1;
in vec2 f_TexCoord0;
in vec3 viewPos;
layout (location=0) out vec4 fragColor;

uniform vec4 ambientMaterial2, diffuseMaterial2, specularMaterial2;
uniform vec4 ambientLight, diffuseLight, specularLight;
uniform mat4 viewMat;
uniform vec4 lightPosition;
uniform float shininess;

void main(void)
{
    vec4 ambientProduct = ambientLight * ambientMaterial2;
    vec4 diffuseProduct = diffuseLight * diffuseMaterial2;
    vec4 specularProduct = specularLight * specularMaterial2;

    vec3 pos = viewPos;
    vec3 nv = cross(dFdx(pos),dFdy(pos));
    nv = nv * sign(nv.z);
    vec3 L = normalize((viewMat*lightPosition).xyz - pos);
    vec3 E = normalize(-pos); 
    vec3 H = normalize(L + E);
    vec3 N = normalize(nv);

    float Kd = max(dot(L, N), 0.0);
    vec4 diffuse = Kd * diffuseProduct;

    vec4 specular = vec4(0.0, 0.0, 0.0, 1.0);
    if (Kd > 0.0f)
    {
        float Ks = pow(max(dot(H, N),1.0),shininess);
        specular = Ks * specularProduct;
    }
    vec4 fragColor_lightning = (ambientProduct + diffuse + specular);
    vec4 fragColor_texture = texture2D(texture1, vec2(f_TexCoord0.x, f_TexCoord0.y));
    fragColor = fragColor_lightning + fragColor_texture;
}

Answer 1

您必须将模型视图投影矩阵拆分为模型视图矩阵和投影矩阵。 使用模型视图矩阵，可以计算视图位置并将其传递给片段着色器。 通过投影矩阵可以计算出裁剪空间的位置。

#version 330 core
layout (location=0) in vec3 in_Position;
layout (location=3) in vec2 in_TexCoord0;

uniform mat4 modelview;
uniform mat4 projection;

out vec2 f_TexCoord0;
out vec3 viewPos;

void main(void)
{
    vec4 pos = modelview * vec4(in_Position, 1.0);;

    f_TexCoord0 = in_TexCoord0;
    viewPos     = pos.xyz;
    gl_Position = projection * pos;
}

有关计算 blinn phong 灯模型，另请参阅 GLSL fixed function fragment program replacement

以某种方式更改您的代码：

in vec3 viewPos;

uniform vec4 lightPosition; // this has to be a view space position
uniform float shininess;

void main()
{
    ....

    vec3 N = cross(dFdx(viewPos.xyz),dFdy(viewPos.xyz));
    N = normalize(N * sign(N.z));

    vec3 L = normalize(lightPosition.xyz - viewPos.xyz);
    vec3 E = normalize(-viewPos.xyz); 
    vec3 H = normalize(L + E);

    float Kd = max(dot(L, N), 0.0);
    vec4 diffuse = Kd * diffuseProduct;

    vec4 specular = vec4(0.0, 0.0, 0.0, 1.0);
    if (Kd > 0.0f)
    {
        float Ks = max(0.0, dot(H, N));
        specular = pow(Ks, shininess) * specularProduct;
    }

    .....
}

---

编辑：

当您执行viewPos = (modelMat * vec4(in_Position, 1.0)).xyz; 时，viewPos 不是视图位置，而是模型位置。要计算视图位置，您必须通过模型矩阵和视图矩阵进行转换：viewPos = (viewMat * modelMat * vec4(in_Position, 1.0)).xyz;。

#version 330 core
layout (location=0) in vec3 in_Position;
layout (location=3) in vec2 in_TexCoord0;

// mvpmatrix is the result of multiplying the model, view, and projection matrices
uniform mat4 mvpmatrix;
uniform mat4 viewMat;
uniform mat4 modelMat;

// Texture coordinate for the fragment shader
out vec2 f_TexCoord0;
out vec3 viewPos;

void main(void)
{
    gl_Position = mvpmatrix * vec4(in_Position, 1.0);
    viewPos = (viewMat * modelMat * vec4(in_Position, 1.0)).xyz;
    f_TexCoord0 = in_TexCoord0;
}

---

我还建议将纹理的颜色乘以浅色：

fragColor = vec4(fragColor_lightning.rgb * fragColor_texture.rgb, fragColor_texture.a);