tinyrenderer-zBuffer隐藏面剔除

绘制物体的深度远近会影响最终投射的效果
画家算法：是z值排序所有物体，从远往近全部绘制，近处物体覆盖远处物体。效率低，且无法处理物体相互穿插的情况

维护一个zBuffer，记录每个像素点的最近zBuffer，根据每个像素点的zBuffer决定绘制哪个物体的颜色

关键点在已知求三角形三个顶点的情况下，求内部任一点的z值。通过重心坐标求解

求重心坐标系数

std::pair<float, float> getBarycentricCoordinates(Vec3f* pts, float x, float y) {
    float beta = ((pts[0].y - pts[1].y) * x + (pts[1].x - pts[0].x) * y + pts[0].x * pts[1].y - pts[1].x * pts[0].y)
        / ((pts[0].y - pts[1].y) * pts[2].x + (pts[1].x - pts[0].x) * pts[2].y + pts[0].x * pts[1].y - pts[1].x * pts[0].y);
    float gamma = ((pts[0].y - pts[2].y) * x + (pts[2].x - pts[0].x) * y + pts[0].x * pts[2].y - pts[2].x * pts[0].y)
        / ((pts[0].y - pts[2].y) * pts[1].x + (pts[2].x - pts[0].x) * pts[1].y + pts[0].x * pts[2].y - pts[2].x * pts[0].y);
    return { beta,gamma };
}

记录zBuffer

std::vector<float> zBuffer(Width * Height, -std::numeric_limits<float>::infinity());

void triangle(Vec3f* pts, TGAImage& image, TGAColor color) {
    float minX = image.get_width() - 1;
    float minY = image.get_height() - 1;
    float maxX = 0;
    float maxY = 0;
    for (int i = 0; i < 3; i++) {
        minX = std::min(minX, pts[i].x);
        maxX = std::max(maxX, pts[i].x);
        minY = std::min(minY, pts[i].y);
        maxY = std::max(maxY, pts[i].y);
    }
    minX = std::max(0.f, minX);
    maxX = std::min(maxX, (float)image.get_width() - 1);
    minY = std::max(0.f, minY);
    maxY = std::min(maxY, (float)image.get_height() - 1);

    for (float x = minX; x <= maxX; x++) {
        for (float y = minY; y <= maxY; y++) {
            auto data = getBarycentricCoordinates(pts, x, y);
            float alpha = 1 - data.first - data.second;
            float beta = data.first;
            float gamma = data.second;
            if (alpha >= 0 && beta >= 0 && gamma >= 0) {
                auto z = alpha * pts[0].z + beta * pts[1].z + gamma * pts[2].z;
                int idx = int(x) + int(y) * Width;
                if (zBuffer[idx] < z) {
                    zBuffer[idx] = z;
                    image.set(x, y, color);
                }
            }
        }
    }
}