GAMES101 Assignment2 (对应Lecture5-6)

课程作业框架来自GAMES

基础部分：

目标要求：正确实现三角形得栅格化算法，测试点是否在三角形内，正确实现z-buffer算法

Rasterizer.cpp

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/*
* 在三角形内检测函数
* parameters:
*		point:x,y
*		triangle:_v
*/
static bool insideTriangle(int x, int y, const Vector3f* _v)
{   
    // TODO : Implement this function to check if the point (x, y) is inside the triangle represented by _v[0], _v[1], _v[2]
    // float xp = x, yp = y;
    // float xa = _v[0].x(), ya = _v[0].y();
    // float xb = _v[1].x(), yb = _v[1].y();
    // float xc = _v[2].x(), yc = _v[2].y();

    // float gamma = ((xb-xa)*(yp-ya)-(xp-xa)*(yb-ya))/((xb-xa)*(yc-ya)-(xc-xa)*(yb-ya));

    // float beta = (xp-xa-gamma*(xc-xa))/(xb-xa);

    // float alpha = 1.0f - gamma - beta;
    
    // return alpha>0 && alpha<1; 

    Vector3f P(x,y,0);
    return ((_v[0]-_v[1]).cross(P-_v[1]).z()<0&&
            (_v[2]-_v[0]).cross(P-_v[0]).z()<0&&
            (_v[1]-_v[2]).cross(P-_v[2]).z()<0);
}

//Screen space rasterization
//此版本为使用MSAA版本，如不使用直接使用insideTriangle函数同时判断z-buffer即可
void rst::rasterizer::rasterize_triangle(const Triangle& t) {
    auto v = t.toVector4();
    
    // TODO : Find out the bounding box of current triangle.
    // iterate through the pixel and find if the current pixel is inside the triangle
    int left_bound = std::min(v[0].x(), std::min(v[1].x(), v[2].x()));
    int right_bound = std::max(v[0].x(), std::max(v[1].x(), v[2].x()));
    int bottom_bound = std::min(v[0].y(), std::min(v[1].y(), v[2].y()));
    int up_bound = std::max(v[0].y(), std::max(v[1].y(), v[2].y()));

    // If so, use the following code to get the interpolated z value.
    //auto[alpha, beta, gamma] = computeBarycentric2D(x, y, t.v);
    //float w_reciprocal = 1.0/(alpha / v[0].w() + beta / v[1].w() + gamma / v[2].w());
    //float z_interpolated = alpha * v[0].z() / v[0].w() + beta * v[1].z() / v[1].w() + gamma * v[2].z() / v[2].w();
    //z_interpolated *= w_reciprocal;

    // TODO : set the current pixel (use the set_pixel function) to the color of the triangle (use getColor function) if it should be painted.
    
    Eigen::Vector3f p;
    for(int x = left_bound;x<=right_bound;x++){
        for (int y = bottom_bound; y <= up_bound; y++)
        {
            // 使用MSAA
            float percent = insideTrianglePercent(x,y,t.v,4);
            if (percent>0)
            {
                auto[alpha, beta, gamma] = computeBarycentric2D(x, y, t.v);
                float w_reciprocal = 1.0/(alpha / v[0].w() + beta / v[1].w() + gamma / v[2].w());
                float z_interpolated = alpha * v[0].z() / v[0].w() + beta * v[1].z() / v[1].w() + gamma * v[2].z() / v[2].w();
                z_interpolated *= w_reciprocal;

                p.x() = x;
                p.y() = y;
                if(z_interpolated < depth_buf[get_index(x,y)]){
                    set_pixel(p,t.getColor(),percent);
                    depth_buf[get_index(x,y)] = z_interpolated;
                }
            }
        }
    }
}

提高部分：

目标要求：实现super-sampling处理反走样

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/* 
* 指定每个像素使用多少个采样点
* parameters:
*	place: x,y
*	vector: _v
*	density: num of sampling
**/
static float insideTrianglePercent(int x, int y, const Vector3f* _v, int density){
    float percent = 0;
    float step = sqrt(density);
    
    // 计算每个采样点的位置参数
    float fragment_spacing = 1.0/step;
    float margin = fragment_spacing/2;
    float weight = 1.0/density;

    for(int i=0;i<step; i++){
        for (int j = 0; j < step; j++)
        {
            percent += insideTriangle(x+margin+fragment_spacing*i,
                        y+margin+fragment_spacing*j,_v)*weight;
        }
        
    }
    return percent;
}