计算机图形学games101作业5

实现光线追踪：

• Renderer.cpp 中的 Render():这里你需要为每个像素生成一条对应的光线，然后调用函数 castRay() 来得到颜色，最后将颜色存储在帧缓冲区的相应像素中。
• Triangle.hpp 中的 rayTriangleIntersect(): v0, v1, v2 是三角形的三个 顶点，orig 是光线的起点，dir 是光线单位化的方向向量。tnear, u, v 是你需 要使用我们课上推导的 Moller-Trumbore 算法来更新的参数。

渲染函数：

```
void Renderer::Render(const Scene& scene)
{
    std::vector<Vector3f> framebuffer(scene.width * scene.height);

    float scale = std::tan(deg2rad(scene.fov * 0.5f));
    float imageAspectRatio = scene.width / (float)scene.height;

    // Use this variable as the eye position to start your rays.
    Vector3f eye_pos(0);
    int m = 0;
    for (int j = 0; j < scene.height; ++j)
    {
        for (int i = 0; i < scene.width; ++i)
        {
            // generate primary ray direction
            float x;
            float y;
            // TODO: Find the x and y positions of the current pixel to get the direction
            // vector that passes through it.
            // Also, don't forget to multiply both of them with the variable *scale*, and
            // x (horizontal) variable with the *imageAspectRatio*            
            //将i,j映射到[-1,1]的空间，其中i,j都加0.5是因为选取像素中间坐标更准确，ny加-号是因为屏幕是从左上角开始计算x,y的
            float nx=(i+0.5f)/(scene.width/2.0f)-1.0f;
            float ny=-((j+0.5f)/(scene.height/2.0f)-1.0f);
            //在视图空间中，默认Near=1,可以计算出w,h
            //h=2*tan(rad/2)*Near,w=h*aspectRadio,那么就可以将[-1,1]中的坐标映射到视图空间中：
            //(nx,ny)--------->(x,y)=(w/2*nx,h/2*ny)
            x=nx*scale*imageAspectRatio;
            y=ny*scale;
            Vector3f dir = Vector3f(x, y, -1); // Don't forget to normalize this direction!
            dir=normalize(dir);
            framebuffer[m++] = castRay(eye_pos, dir, scene, 0);
        }
        UpdateProgress(j / (float)scene.height);
    }

    // save framebuffer to file
    FILE* fp = fopen("binary.ppm", "wb");
    (void)fprintf(fp, "P6\n%d %d\n255\n", scene.width, scene.height);
    for (auto i = 0; i < scene.height * scene.width; ++i) {
        static unsigned char color[3];
        color[0] = (char)(255 * clamp(0, 1, framebuffer[i].x));
        color[1] = (char)(255 * clamp(0, 1, framebuffer[i].y));
        color[2] = (char)(255 * clamp(0, 1, framebuffer[i].z));
        fwrite(color, 1, 3, fp);
    }
    fclose(fp);    
}
```

对Möller Trumbore算法的简单运用求三角形和线的交点

//求三角形和射线的交点，并把相应数据写入对应变量
bool rayTriangleIntersect(const Vector3f& v0, const Vector3f& v1, const Vector3f& v2, const Vector3f& orig,
                          const Vector3f& dir, float& tnear, float& u, float& v)
{
    // TODO: Implement this function that tests whether the triangle
    // that's specified bt v0, v1 and v2 intersects with the ray (whose
    // origin is *orig* and direction is *dir*)
    // Also don't forget to update tnear, u and v.
    //对Möller Trumbore算法应用
    Vector3f e1=v1-v0;
    Vector3f e2=v2-v0;
    Vector3f s=orig-v0;
    Vector3f s1= crossProduct(dir,e2);
    Vector3f s2= crossProduct(s,e1);
    float s1e1=1.f/ dotProduct(s1,e1);
    Vector3f mv(dotProduct(s2,e2), dotProduct(s1,s), dotProduct(s2,dir));
    float t=s1e1*mv.x;
    float b1=s1e1*mv.y;
    float b2=s1e1*mv.z;
    if(t>0&&b1>0&&b2>0&&(1-b1-b2)>0){
        tnear=t;
        u=b1;
        v=b2;
        return true;
    }
    return false;
}