OpenGL - 如何在不旋轉對象的情況下同時旋轉光源？

Question

我正在做 learnopengl 教程，我正在嘗試基本照明教程中的練習之一 -

嘗試使用 sin 或 cos 隨時間在場景周圍移動光源。

雖然在我的情況下，我使用的是 SDL，這意味着我不能使用以下方程來旋轉我的光源：

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

現在，當我旋轉我的對象時，我的光源會隨之旋轉，但是我希望我的光源與我的對象分開旋轉。 這就是我在渲染循環中處理燈光和對象旋轉的內容：

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]);
}

這就是我的頂點着色器中的內容：

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);
}

如何僅旋轉光源而不旋轉物體？

Answer 1

如果要旋轉光源，則必須變換lightPos而不是旋轉模型。 這也更有效，因為它每幀只需要一個矩陣變換（而不是每個頂點一個）。 代碼應如下所示：

// 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);

頂點着色器：

// 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;
}

片段着色器保持原樣。