C++ 渲染函数解析：生成主光线并投射到场景

这是一个渲染函数，用于生成主光线并将这些光线投射到场景中，最终将渲染结果保存到文件中。

首先创建一个大小为场景宽度和高度乘积的像素缓冲区。

std::vector<Vector3f> framebuffer(scene.width * scene.height);

计算缩放因子，这里使用了 tan 函数将场景的视角转换为缩放因子。

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

计算图像的宽高比。

float imageAspectRatio = (float)scene.width / (float)scene.height;

设置眼睛位置为原点。

Vector3f eye_pos(0);

使用嵌套循环遍历所有像素，生成主光线方向，计算出当前像素的位置，然后将其乘以缩放因子。

for (int j = 0; j < scene.height; ++j)
{
    for (int i = 0; i < scene.width; ++i)
    {
        // generate primary ray direction
        float x = (2*(((float)i+0.5)/scene.width-1) * imageAspectRatio * scale;
        float y = (1.0-2*((float)j+0.5)/scene.height) * scale;
        // 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*    
           
        //vector = op,说明scene在z=-1，故znear距离人眼距离=1   
        Vector3f dir = normalize(Vector3f(x, y, -1)); // Don't forget to normalize this direction!
        framebuffer[m++] = castRay(eye_pos, dir, scene, 0);
    }
    UpdateProgress(j / (float)scene.height);
}

将主光线方向归一化，然后将其传递给 castRay 函数，该函数将返回相应的颜色值，将其存储在像素缓冲区中。

Vector3f dir = normalize(Vector3f(x, y, -1)); // Don't forget to normalize this direction!
framebuffer[m++] = castRay(eye_pos, dir, scene, 0);

将像素缓冲区保存到文件中。

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);

注：在渲染过程中，还调用了 UpdateProgress 函数来更新进度条。