# 2020q3 Homework5 (render)

contributed by < `blueskyson` >

###### tags: `linux2020`

## 目錄

[TOC]

## Trace Code

在 `main.cpp` 的 `main` 中，首先使用 `SDL_Init(SDL_INIT_VIDEO)` 初始化視訊媒體

int main(int argc, char *args[])
{
    if (SDL_Init(SDL_INIT_VIDEO) < 0) {
        printf("SDL could not initialize! SDL_Error: %s\n", SDL_GetError());
    } else {

接下來初始化遊戲視窗 `SDL_Window` ，以下是 `SDL_CreateWindow` 的參數說明:

- **title** The title of the window, in UTF-8 encoding.
- **x** The x position of the window, `::SDL_WINDOWPOS_CENTERED`, or `::SDL_WINDOWPOS_UNDEFINED`.
- **y** The y position of the window, `::SDL_WINDOWPOS_CENTERED`, or `::SDL_WINDOWPOS_UNDEFINED`.
- **w** The width of the window, in screen coordinates.
- **h** The height of the window, in screen coordinates.
- **flags** The flags for the window, a mask of any of the following:
`::SDL_WINDOW_FULLSCREEN`, `::SDL_WINDOW_OPENGL`, `::SDL_WINDOW_HIDDEN`, `::SDL_WINDOW_BORDERLESS`, `::SDL_WINDOW_RESIZABLE`, `::SDL_WINDOW_MAXIMIZED`, `::SDL_WINDOW_MINIMIZED`,`::SDL_WINDOW_INPUT_GRABBED`, `::SDL_WINDOW_ALLOW_HIGHDPI`,
`::SDL_WINDOW_VULKAN`

        /* 在 raycaster.h 中有宣告要傳入 SDL_CreateWindow 的參數
         * #define SCREEN_WIDTH (uint16_t) 320
         * #define SCREEN_HEIGHT (uint16_t) 256
         * #define SCREEN_SCALE 2
         */
        SDL_Window *sdlWindow =
            SDL_CreateWindow("RayCaster [fixed-point vs. floating-point]",
                             SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
                             SCREEN_SCALE * (SCREEN_WIDTH * 2 + 1),
                             SCREEN_SCALE * SCREEN_HEIGHT, SDL_WINDOW_SHOWN);

確認 `SDL_Window` 是否成功初始化

        if (sdlWindow == NULL) {
            printf("Window could not be created! SDL_Error: %s\n",
                   SDL_GetError());
        } else {

接下來初始化遊戲中會用到的物件，首先初始化 `Game` 物件， `Game` 物件中包含

- `float playerX, playerY, playerA;` 代表玩家的位置和視角
- `void Move(int m, int r, float seconds);` 用來控制玩家移動

            Game game;

初始化 `RayCasterFloat` ， `RayCasterFloat` 物件有計算光線投射的方法
初始化 `RayCasterFloat` 物件，搭配 `RayCasterFloat` 可以完成浮點數算繪
目前還不知道 `floatBuffer` 的用途

            RayCasterFloat floatCaster;
            Renderer floatRenderer(&floatCaster);
            uint32_t floatBuffer[SCREEN_WIDTH * SCREEN_HEIGHT];

跟 21 到 23 行類似，初始化定點數的算繪

            RayCasterFixed fixedCaster;
            Renderer fixedRenderer(&fixedCaster);
            uint32_t fixedBuffer[SCREEN_WIDTH * SCREEN_HEIGHT];

初始化以下變數

            int moveDirection = 0;        // 玩家的移動方向
            int rotateDirection = 0;      // 玩家的轉動方向
            bool isExiting = false;       // 是否已離開遊戲
            /* 根據 SDL 解析度所得到的刷新頻率 */
            const static auto tickFrequency = SDL_GetPerformanceFrequency();
            /* 獲得目前 SDL Counter 的值 */
            auto tickCounter = SDL_GetPerformanceCounter();
            SDL_Event event;              // 儲存目前的 key code

            /* 用來接收 fixedTexture 和 floatTexture 的值
             * 並且暫存下一個 frame 要繪製的資訊 */
            SDL_Renderer *sdlRenderer =
                SDL_CreateRenderer(sdlWindow, -1, SDL_RENDERER_ACCELERATED);
            
            /* 用來接收 fixedBuffer 的值，以 SDL_Texture 型態表示 */
            SDL_Texture *fixedTexture = SDL_CreateTexture(
                sdlRenderer, SDL_PIXELFORMAT_ARGB8888,
                SDL_TEXTUREACCESS_STREAMING, SCREEN_WIDTH, SCREEN_HEIGHT);
            
            /* 用來接收 floatBuffer 的值，以 SDL_Texture 型態表示 */
            SDL_Texture *floatTexture = SDL_CreateTexture(
                sdlRenderer, SDL_PIXELFORMAT_ARGB8888,
                SDL_TEXTUREACCESS_STREAMING, SCREEN_WIDTH, SCREEN_HEIGHT);

接下來進入 while 迴圈，玩家按下 Esc 或關閉遊戲視窗才會跳出迴圈

            while (!isExiting) {
                floatRenderer.TraceFrame(&game, floatBuffer);
                fixedRenderer.TraceFrame(&game, fixedBuffer);

                DrawBuffer(sdlRenderer, fixedTexture, fixedBuffer, 0);
                DrawBuffer(sdlRenderer, floatTexture, floatBuffer,
                           SCREEN_WIDTH + 1);

                SDL_RenderPresent(sdlRenderer);

                if (SDL_PollEvent(&event)) {
                    isExiting =
                        ProcessEvent(event, &moveDirection, &rotateDirection);
                }
                const auto nextCounter = SDL_GetPerformanceCounter();
                const auto seconds = (nextCounter - tickCounter) /
                                     static_cast<float>(tickFrequency);
                tickCounter = nextCounter;
                game.Move(moveDirection, rotateDirection, seconds);
            }
            SDL_DestroyTexture(floatTexture);
            SDL_DestroyTexture(fixedTexture);
            SDL_DestroyRenderer(sdlRenderer);
            SDL_DestroyWindow(sdlWindow);
        }
    }

    SDL_Quit();
    return 0;
}

## 待續