如何在我的 raycaster 中修复扭曲的墙壁？

Question

我正在使用 SDL 库和 C 编写一个 raycaster。我已经处理鱼眼效果好几个星期了。对于像 60 度这样的视野，我将到墙的距离乘以相对角度的余弦值（范围从 -30 到 30），但仍然得到相同的鱼眼。这是它的样子：

我现在不知道该怎么做，因为有这么多来源推荐了余弦校正，但它并没有解决我的失真问题。

我是这样编译的： clang `pkg-config --cflags --libs sdl2` raycaster.c
要前进和后退，请按向上和向下键。按左和右扫射。您可以使用 a 和 s 键分别向左和向右转。

我的代码在下面，如果你想看的话。如果您设法弄清楚为什么我的引擎中出现扭曲的视角，请告诉我。

#include <SDL2/SDL.h>
#include <math.h>

#define SET_COLOR(r, g, b) SDL_SetRenderDrawColor(renderer, r, g, b, SDL_ALPHA_OPAQUE)

typedef struct {
    float x, y, prev_x, prev_y, angle, fov;
} Player;

enum {
    map_width = 12, map_height = 15,
    screen_width = 800, screen_height = 500
};

const float
    move_speed_decr = 0.08,
    angle_turn = 2.0,
    theta_step = 0.05,
    dist_step = 0.8,
    width_ratio = (float) screen_width / map_width,
    height_ratio = (float) screen_height / map_height;

const unsigned char map[map_height][map_width] = {
    {1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1},
    {1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1},
    {1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1},
    {1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1},
    {1, 0, 1, 1, 1, 0, 0, 0, 1, 0, 0, 1},
    {1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1},
    {1, 0, 0, 0, 1, 1, 1, 1, 1, 0, 0, 1},
    {1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1},
    {1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1},
    {1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1},
    {1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1},
    {1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1},
    {1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1},
    {1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1},
    {1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1}
};

SDL_Window* window;
SDL_Renderer* renderer;

float to_radians(float degrees) {
    return degrees * (M_PI / 180.0f);
}

void draw_rectangle(SDL_Rect rectangle, int r, int g, int b) {
    SET_COLOR(r, g, b);
    SDL_RenderFillRect(renderer, &rectangle);
    SDL_RenderDrawRect(renderer, &rectangle);
}

void raycast(Player player) {
    SET_COLOR(210, 180, 140);

    float
        half_fov = player.fov / 2,
        rel_x = player.x * width_ratio, rel_y = player.y * height_ratio;

    float screen_x = 0, step_x = (screen_width / player.fov) * theta_step;

    for (float theta = player.angle - half_fov; theta < player.angle + half_fov; theta += theta_step) {
        float rad_theta = to_radians(theta);
        float cos_theta = cos(rad_theta), sin_theta = sin(rad_theta);

        float dist = 0;
        while (dist += dist_step) {
            float
                new_x = cos_theta * dist + rel_x,
                new_y = sin_theta * dist + rel_y;

            if (map[(int) (new_y / height_ratio)][(int) (new_x / width_ratio)]) {
                dist *= cos(to_radians(theta - player.angle));
                float double_dist = 2 * dist;

                if (double_dist >= screen_height) break;
                SDL_Rect column = {screen_x, dist, step_x + 1, screen_height - double_dist};

                SDL_RenderFillRect(renderer, &column);
                SDL_RenderDrawRect(renderer, &column);
                break;
            }
        }
        screen_x += step_x;
    }
}

void handle_input(const Uint8* keys, Player* player) {
    SDL_Event event;

    while (SDL_PollEvent(&event)) {
        if (event.type == SDL_QUIT) {
            SDL_DestroyWindow(window);
            SDL_DestroyRenderer(renderer);
            exit(0);
        }

        else if (event.type == SDL_KEYDOWN) {
            float radian_theta = to_radians(player -> angle);
            float move_x = cos(radian_theta) * move_speed_decr,
                move_y = sin(radian_theta) * move_speed_decr;

            // handle arrow keys
            if (keys[SDL_SCANCODE_UP]) player -> x += move_x, player -> y += move_y;
            if (keys[SDL_SCANCODE_DOWN]) player -> x -= move_x, player -> y -= move_y;
            if (keys[SDL_SCANCODE_LEFT]) player -> x += move_y, player -> y -= move_x;
            if (keys[SDL_SCANCODE_RIGHT]) player -> x -= move_y, player -> y += move_x;

            // handle 'a' and 's' for angle changes
            if (keys[SDL_SCANCODE_A]) player -> angle -= angle_turn;
            if (keys[SDL_SCANCODE_S]) player -> angle += angle_turn;

            // safeguards for invalid positions and angles
            if (player -> x < 0) player -> x = 0;
            else if (player -> x > screen_width) player -> x = screen_width;

            if (player -> y < 0) player -> y = 0;
            else if (player -> y > screen_height) player -> y = screen_height;

            // move the player to their previous coordinate if they're in a wall
            if (map[(int) player -> y][(int) player -> x])
                player -> y = player -> prev_y, player -> x = player -> prev_x;

            if (player -> angle > 360) player -> angle = 0;
            else if (player -> angle < 0) player -> angle = 360;

            player -> prev_y = player -> y, player -> prev_x = player -> x;
        }
    }
}

int main() {
    SDL_CreateWindowAndRenderer(screen_width, screen_height, 0, &window, &renderer);
    SDL_SetWindowTitle(window, "Raycaster");    

    Player player = {5, 5, 0, 0, 0, 60};
    SDL_Rect the_ceiling = {0, 0, screen_width, screen_height / 2};
    SDL_Rect the_floor = {0, screen_height / 2, screen_width, screen_height};
    const Uint8* keys = SDL_GetKeyboardState(NULL);

    while (1) {
        handle_input(keys, &player);

        draw_rectangle(the_ceiling, 96, 96, 96);
        draw_rectangle(the_floor, 255,69,0);

        raycast(player);

        SDL_RenderPresent(renderer);
        SDL_UpdateWindowSurface(window);
    }
}

Answer 1

这段代码有两个主要问题。必须计算光线与墙的交点到墙的距离，而不是仅仅依赖于端点位于墙正方形内。

在 C 有一个摄像头，通过从 A 和 B 之间足够数量的点投射来自 C 的光线来解决失真，只需将这个平面（您的屏幕）划分为同样宽的列（像素）。

我对余弦校正相当悲观，因为据我所知，与列高相比，应该更有可能调整绘制的列宽或位置。

Answer 2

您需要应用以下差异：

diff --git a/so33.c b/so33.c
index e65cff8..b0f6d8a 100644
--- a/so33.c
+++ b/so33.c
@@ -56,7 +56,7 @@ void raycast(Player player) {
 
     float
         half_fov = player.fov / 2,
-        rel_x = player.x * width_ratio, rel_y = player.y * height_ratio;
+        rel_x = player.x, rel_y = player.y;
 
     float screen_x = 0, step_x = (screen_width / player.fov) * theta_step;
 
@@ -70,12 +70,12 @@ void raycast(Player player) {
                 new_x = cos_theta * dist + rel_x,
                 new_y = sin_theta * dist + rel_y;
 
-            if (map[(int) (new_y / height_ratio)][(int) (new_x / width_ratio)]) {
+            if (map[(int) (new_y)][(int) (new_x)]) {
                 dist *= cos(to_radians(theta - player.angle));
-                float double_dist = 2 * dist;
-
-                if (double_dist >= screen_height) break;
-                SDL_Rect column = {screen_x, dist, step_x + 1, screen_height - double_dist};
+               float wall_height = screen_height / dist;
+               if (wall_height > screen_height)
+                       wall_height = screen_height;
+                SDL_Rect column = {screen_x, screen_height/2 - wall_height/2, step_x + 1, wall_height};
 
                 SDL_RenderFillRect(renderer, &column);
                 SDL_RenderDrawRect(renderer, &column);

发现了一些问题。

系数 width_ratio 和 height_ratio 似乎混合了地图中的坐标 space 和屏幕中的坐标 space。这是毫无意义的。此外，它通过沿特定轴移动得更快来破坏导航。
将 dist 投影到通过屏幕中心投射的光线后（dist *= cos(...) 你必须应用简单的透视来计算墙的高度（变量 wall_height)
最后，围绕中间水平线画一个高度wall_height的矩形。

编辑。放 dist_step = 0.01

如何在我的 raycaster 中修复扭曲的墙壁？

How do I fix warped walls in my raycaster?

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