Question

我尝试遵循this tutorial的有关OpenGL中鼠标拾取的信息，但是我无法使其正常工作。

根据我的基本理解，要从鼠标坐标中获取世界空间坐标，我需要乘以一堆逆矩阵。然后，要从局部空间获取世界空间坐标，可以将局部空间坐标与模型矩阵相乘。但是我得到的坐标彼此不一致。

我试图归一化模型的世界坐标，因为鼠标坐标也被归一化了，但是我不确定是否是这种情况。

if (instance && button == GLFW_MOUSE_BUTTON_LEFT
    && action == GLFW_PRESS) {
    glfwGetCursorPos(window, &x, &y);

    pMat = instance->graphics->getPMat();

    cameraPos = instance->graphics->getCameraPos();

    //View matrix
    vMat = glm::translate(glm::mat4(1.0f), glm::vec3(cameraPos.x, cameraPos.y, -cameraPos.z));
    //vMat = glm::rotate(vMat, 0.6f, glm::vec3(1.0f, 0.0f, 0.0f));

    //normalized mouse coordinates
    x = (2.0f * x) / width - 1.0f;
    y = 1.0 - (2.0f * y) / height;

    glm::vec3 ray_nds = glm::vec3(x, y, 1.0f);

    glm::vec4 ray_clip = glm::vec4(ray_nds.x, ray_nds.y, -1.0, 1.0);

    glm::vec4 ray_eye = glm::inverse(pMat) * ray_clip;
    ray_eye = glm::vec4(ray_eye.x, ray_eye.y, -1.0, 0.0f);

    glm::vec3 ray_wor = glm::vec4(glm::inverse(vMat) * ray_eye);
    ray_wor = glm::normalize(ray_wor);

    Entity* e = instance->getCurrentScene().getEntities()[0];

    sMat = glm::scale(glm::mat4(1.0f), glm::vec3(e->getScaleX(), e->getScaleY(), e->getScaleZ()));
    tMat = glm::translate(glm::mat4(1.0f), glm::vec3(e->getX(), e->getY(), e->getZ()));

    rMat = glm::rotate(glm::mat4(1.0f), e->getRotY(), glm::vec3(0.0f, 1.0f, 0.0f));
    rMat = glm::rotate(rMat, e->getRotX(), glm::vec3(1.0f, 0.0f, 0.0f));
    rMat = glm::rotate(rMat, e->getRotZ(), glm::vec3(0.0f, 0.0f, 1.0f));

    mMat = tMat * rMat * sMat;
    mvMat = vMat * mMat;

    startCoords = mMat * glm::vec4(0.0f, 0.0f, 0.0f, 1.0f);
    startCoords = glm::normalize(startCoords);
    endCoords = mMat * glm::vec4(1.0f, -1.0f, 1.0f, 1.0f);
    endCoords = glm::normalize(endCoords);

    if (ray_wor.x >= startCoords.x
        && ray_wor.y <= startCoords.y
        && ray_wor.x <= endCoords.x
        && ray_wor.y >= endCoords.y) {
        std::cout << "\nFound!\n";
    }

    std::cout << "x: " << ray_wor.x << "\n"
        << "y: " << ray_wor.y << "\n"
        << "z: " << ray_wor.z << "\n\n";

    std::cout << "x: " << endCoords.x << "\n"
        << "y: " << endCoords.y << "\n"
        << "z: " << endCoords.z << "\n\n";

    std::cout << "x: " << startCoords.x << "\n"
        << "y: " << startCoords.y << "\n"
        << "z: " << startCoords.z << "\n\n";
}

Answer 1

投影矩阵从视图空间转换为剪辑空间。在透视投影时，剪辑空间坐标为Homogeneous coordinates。从剪辑空间到规范化的设备空间的转换是通过Perspective divide完成的。

要从规范化的设备空间转换为视图空间，您需要做相反的事情：

// normalized device coordiantes
glm::vec3 nds_near = glm::vec4(x, y, -1.0f, 1.0f);

// view coordiantes
glm::vec4 eye_h = glm::inverse(pMat) * nds_near;
glm::vec4 ray_eye = glm::vec4(eye_h.x/eye_h.w, eye_h.y/eye_h.w, eye_h.z/eye_h.w, 1.0f);

// world coordinates
glm::vec3 ray_wor = glm::vec4(glm::inverse(vMat) * ray_eye);
ray_wor = glm::normalize(ray_wor);

在OpenGL中使用射线投射进行鼠标拾取？

1 个答案: