OpenGL - 如何在不旋转物体的同时旋转光源？

Question

我正在学习 learnopengl 教程，并且正在尝试基本照明教程中的练习之一 -

尝试随着时间的推移在场景中移动光源 罪或因。

虽然就我而言，我使用的是 SDL，这意味着我不能使用以下方程式来旋转我的光源：

lightPos.x = 1.0f + sin(glfwGetTime()) * 2.0f;
lightPos.y = sin(glfwGetTime() / 2.0f) * 1.0f;

现在，当我旋转我的对象时，我的光源会随之旋转，但是我希望我的光源与我的对象分开旋转。这是我在渲染循环中处理灯光和对象旋转的内容：

void OpenGLWindow::render()
{

    lightPos.x = 1.0f + sin(SDL_GetTicks()/1000.0f) * 2.0f;
    lightPos.y = sin((SDL_GetTicks()/1000.0f) / 2.0f) * 1.0f;

    glm::mat4 model(1.0f);
    //model = glm::translate(model, lightPos);
    model = glm::rotate(model, lightPos.z, glm::vec3(0.0f, 0.0f, 1.0f));
    //model = glm::rotate(model, lightPos.y, glm::vec3(0.0f, 1.0f, 0.0f));
    model = glm::rotate(model, lightPos.x, glm::vec3(1.0f, 0.0f, 0.0f));
    int modelMatLocation = glGetUniformLocation(shader, "lightMatrix");
    glUniformMatrix4fv(modelMatLocation, 1, false, &model[0][0]);

    // NOTE: glm::translate/rotate/scale apply the transformation by right-multiplying by the
    //       corresponding transformation matrix (T). IE glm::translate(M, v) = M * T, not T*M
    //       This means that the transformation you apply last, will effectively occur first
    glm::mat4 modelMat(1.0f);
    modelMat = glm::translate(modelMat, parentEntity.position);
    modelMat = glm::rotate(modelMat, parentEntity.rotation.z, glm::vec3(0.0f, 0.0f, 1.0f));
    modelMat = glm::rotate(modelMat, parentEntity.rotation.y, glm::vec3(0.0f, 1.0f, 0.0f));
    modelMat = glm::rotate(modelMat, parentEntity.rotation.x, glm::vec3(1.0f, 0.0f, 0.0f));
    modelMat = glm::scale(modelMat, parentEntity.scale);
    int modelMatrixLoc = glGetUniformLocation(shader, "modelMatrix");
    glUniformMatrix4fv(modelMatrixLoc, 1, false, &modelMat[0][0]);
}

这就是我的顶点着色器中的内容：

in vec3 position;
out vec3 FragPos;
out vec3 Normal;

uniform mat4 projectionMatrix;
uniform mat4 viewingMatrix;
uniform mat4 modelMatrix;
uniform mat4 lightMatrix;

void main()
{
    vec4 transformedPosition = projectionMatrix * viewingMatrix * modelMatrix * lightMatrix * vec4(position, 1.0f);

    gl_Position = transformedPosition;
    FragPos = vec3(modelMatrix * vec4(position, 1.0));
    Normal = mat3(transpose(inverse(modelMatrix))) * position;
}

片段着色器：

out vec4 outColor;
in vec3 Normal;
in vec3 FragPos;

uniform vec3 lightPos;
uniform vec3 objectColor;
uniform vec3 lightColor;
uniform vec3 viewPos;

void main()
{
    float ambientStrength = 0.06;
    vec3 ambient = ambientStrength * lightColor;

    vec3 norm = normalize(Normal);
    vec3 lightDir = normalize(lightPos - FragPos);
    float diff = max(dot(norm, lightDir), 0.0);
    vec3 diffuse = diff * lightColor;

    float specularStrength = 0.6;
    vec3 viewDir = normalize(viewPos - FragPos);
    vec3 reflectDir = reflect(-lightDir, norm);
    float spec = pow(max(dot(viewDir, reflectDir), 0.0), 32);
    vec3 specular = specularStrength * spec * lightColor;
    vec3 result = (ambient + diffuse + specular) * objectColor;
    outColor = vec4(result, 1.0);
}

如何只旋转光源而不旋转物体？

Answer 1

如果要旋转光源，则必须变换lightPos 而不是旋转模型。这也更有效，因为它每帧只需要一个矩阵变换（而不是每个顶点一个）。代码应如下所示：

// C++
glm::vec4 lightPos(...) // <-- The light position you currently use

glm::mat4 lightM(1.0f);
lightM = glm::rotate(lightM, lightRotation.z, glm::vec3(0.0f, 0.0f, 1.0f));
lightM = glm::rotate(lightM, lightRotation.y, glm::vec3(0.0f, 1.0f, 0.0f));
lightM = glm::rotate(lightM, lightRotation.x, glm::vec3(1.0f, 0.0f, 0.0f));

glm::vec4 rotatedLightPos = lightM * lightPos;

glUniform3f(lightPosLocation, rotatedLightPos.x, rotatedLightPos.y, rotatedLightPos.z);

顶点着色器：

// GLSL
in vec3 position;
out vec3 FragPos;
out vec3 Normal;

uniform mat4 projectionMatrix;
uniform mat4 viewingMatrix;
uniform mat4 modelMatrix;

void main()
{
    vec4 transformedPosition = projectionMatrix * viewingMatrix * modelMatrix * vec4(position, 1.0f);

    gl_Position = transformedPosition;
    FragPos = vec3(modelMatrix * vec4(position, 1.0));
    Normal = mat3(transpose(inverse(modelMatrix))) * position;
}

片段着色器保持原样。