demo

PBR直接光源

• 顾名思义：直接光源指有光源直接照射到点p 的辐射强度，由于一个光源只会有一个光线wi影响点p，所以和之前的计算没什么差异
• 对于影响p的光源，并不需要积分计算半球形辐照度，遍历每个影响点p的光源计算辐射率（单一方向的影响），再将所有光源求和计算，
• 最后考虑BRDF来缩放辐射率
• 但这次需要按照PBR的方程，计算出基于物理模型的渲染图元
• F0，被称为0°入射角的基础反射率，会随着与平面法线的夹角增加而增大

球体（顶点数据）：

        //4096个顶点，绘制整个球体，按照经度半圈半圈，自上到下绘制，最后所有经度线都离散的绘制了
        for (unsigned int x = 0; x <= X_SEGMENTS; ++x)//纬度有64个顶点
        {
            for (unsigned int y = 0; y <= Y_SEGMENTS; ++y)//每个经度半圈有64个顶点
            {
                float xSegment = (float)x / (float)X_SEGMENTS;//分隔绕y轴的角度
                float ySegment = (float)y / (float)Y_SEGMENTS;//分隔绕x或z的角度，

                float xPos = std::cos(xSegment * 2.0f * PI) * std::sin(ySegment * PI);//弧度制
                float yPos = std::cos(ySegment * PI);//
                float zPos = std::sin(xSegment * 2.0f * PI) * std::sin(ySegment * PI);//

                s_SphereData.positions.push_back(glm::vec3(xPos, yPos, zPos));
                s_SphereData.uv.push_back(glm::vec2(xSegment, ySegment));
                s_SphereData.normals.push_back(glm::vec3(xPos, yPos, zPos));
            }
        }
        //上面仅仅是绘制了平面的4个顶点，实则需要6个顶点，
        for (int i = 0; i < Y_SEGMENTS; i++)//第0个顶点和第65个顶点对齐，相邻的维度，绘制3角形
        {
            for (int j = 0; j < X_SEGMENTS; j++)
            {

                 s_SphereData.indices.push_back(i * (X_SEGMENTS + 1) + j);
                 s_SphereData.indices.push_back((i + 1) * (X_SEGMENTS + 1) + j);
                 s_SphereData.indices.push_back((i + 1) * (X_SEGMENTS + 1) + j + 1);
                 
                 s_SphereData.indices.push_back(i * (X_SEGMENTS + 1) + j);
                 s_SphereData.indices.push_back((i + 1) * (X_SEGMENTS + 1) + j + 1);
                 s_SphereData.indices.push_back(i * (X_SEGMENTS + 1) + j + 1);
            }
        }

        s_SphereData.indexCount = static_cast<unsigned int>(s_SphereData.indices.size());
        //data将每个顶点的三个数据和为一个-》最终每个顶点的数据

        for (unsigned int i = 0; i < s_SphereData.positions.size(); ++i)
        {
             s_SphereData.data.push_back( s_SphereData.positions[i].x);
             s_SphereData.data.push_back( s_SphereData.positions[i].y);
             s_SphereData.data.push_back( s_SphereData.positions[i].z);
            if (s_SphereData.normals.size() > 0)
            {
                 s_SphereData.data.push_back( s_SphereData.normals[i].x);
                 s_SphereData.data.push_back( s_SphereData.normals[i].y);
                 s_SphereData.data.push_back( s_SphereData.normals[i].z);
            }
            if (s_SphereData.uv.size() > 0)
            {
                 s_SphereData.data.push_back( s_SphereData.uv[i].x);
                 s_SphereData.data.push_back( s_SphereData.uv[i].y);
            }
        }