C++ 什么是 SDL 渲染器？

What is an SDL renderer?

提问by prcastro

I'm starting with SDL2 and having some trouble trying to understand what an SDL_Renderer is.

我从 SDL2 开始，在试图理解 SDL_Renderer 是什么时遇到了一些麻烦。

What is it? What does it do? What's the difference between SDL_Renderer, SDL_Window, SDL_Surface and SDL_Texture and how they are related?

它是什么？它有什么作用？SDL_Renderer、SDL_Window、SDL_Surface 和 SDL_Texture 之间有什么区别以及它们之间的关系？

I had issues with this when trying to understand this introductory code:

在尝试理解这段介绍性代码时，我遇到了这个问题：

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

int main()
{
    /* Starting SDL */
    if (SDL_Init(SDL_INIT_EVERYTHING) != 0) {
        std::cout << "SDL_Init Error: " << SDL_GetError() << std::endl;
        return 1;
    }

    /* Create a Window */
    SDL_Window *window = SDL_CreateWindow("Hello World!", 100, 100, 640, 480, SDL_WINDOW_SHOWN);
    if (window == nullptr) {
        std::cout << "SDL_CreateWindow Error: " << SDL_GetError() << std::endl;
        return 1;
    }

    /* Create a Render */
    SDL_Renderer *render = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
    if (render == nullptr) {
        std::cout << "SDL_CreateRenderer Error: " << SDL_GetError() << std::endl;
        return 1;
    }

    /* Load bitmap image */
    SDL_Surface *bmp = SDL_LoadBMP("./Tutorial/res/Lesson1/hello.bmp");
    if (bmp == nullptr) {
        std::cout << "SDL_LoadBMP Error: " << SDL_GetError() << std::endl;
        return 1;
    }

    /* Upload surface to render, and then, free the surface */
    SDL_Texture *texture = SDL_CreateTextureFromSurface(render, bmp);
    SDL_FreeSurface(bmp);
    if (texture == nullptr){
        std::cout << "SDL_CreateTextureFromSurface Error: " << SDL_GetError() << std::endl;
        return 1;
    }

    /* Draw the render on window */
    SDL_RenderClear(render); // Fill render with color
    SDL_RenderCopy(render, texture, NULL, NULL); // Copy the texture into render
    SDL_RenderPresent(render); // Show render on window

    /* Wait 2 seconds */
    SDL_Delay(5000);

    /* Free all objects*/
    SDL_DestroyTexture(texture);
    SDL_DestroyRenderer(render);
    SDL_DestroyWindow(window);

    /* Quit program */
    SDL_Quit();
    return 0;
}

I was using Twinklebear tutorial (suggested on SDL Wiki) and looked also on SDL Wiki Documentation and some books. But all of them assume that I know these definitions.

我正在使用 Twinklebear 教程（在 SDL Wiki 上建议）并查看了 SDL Wiki 文档和一些书籍。但他们都假设我知道这些定义。

回答by olevegard

SDL_Window

SDL_Window

SDL_Windowis the struct that holds all info about the Window itself: size, position, full screen, borders etc.

SDL_Window是保存有关窗口本身的所有信息的结构：大小、位置、全屏、边框等。

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SDL_Renderer

SDL_Renderer

SDL_Rendereris a struct that handles all rendering. It is tied to a SDL_Windowso it can only render within that SDL_Window. It also keeps track the settings related to the rendering. There are several important functions tied to the SDL_Renderer

SDL_Renderer是一个处理所有渲染的结构体。它与 a 相关联，SDL_Window因此只能在其中渲染SDL_Window。它还跟踪与渲染相关的设置。有几个重要的功能与SDL_Renderer

• SDL_SetRenderDrawColor(renderer, r, g, b, a);
  This sets the color you clear the screen to ( see below )

• SDL_RenderClear(renderer);
  This clears the rendering target with the draw color set above

• SDL_RenderCopy(
  This is probably the function you'll be using the most, it's used for rendering a SDL_Textureand has the following parameters :

  • SDL_Renderer* renderer,
    The renderer you want to use for rendering.
  • SDL_Texture* texture,
    The texture you want to render.
  • const SDL_Rect* srcrect,The part of the texture you want to render, NULL if you want to render the entire texture
  • const SDL_Rect* dstrect)
    Where you want to render the texture in the window. If the width and height of this SDL_Rectis smaller or larger than the dimensions of the texture itself, the texture will be stretched according to this SDL_Rect
• SDL_RenderPresent(renderer);
  The other SDL_Render* functions draws to a hidden target. This function will take all of that and draw it in the window tied to the renderer.

• SDL_SetRenderDrawColor(renderer, r, g, b, a);
  这会将您清除屏幕的颜色设置为（见下文）

• SDL_RenderClear(renderer);
  这将使用上面设置的绘制颜色清除渲染目标

• SDL_RenderCopy(
  这可能是您最常使用的函数，它用于渲染 aSDL_Texture并具有以下参数：

  • SDL_Renderer* renderer,
    要用于渲染的渲染器。
  • SDL_Texture* texture,
    要渲染的纹理。
  • const SDL_Rect* srcrect,要渲染的纹理部分，如果要渲染整个纹理，则为 NULL
  • const SDL_Rect* dstrect)
    要在窗口中渲染纹理的位置。如果 this 的宽度和高度SDL_Rect小于或大于纹理本身的尺寸，则纹理将根据此拉伸SDL_Rect
• SDL_RenderPresent(renderer);
  其他 SDL_Render* 函数绘制到隐藏目标。此函数将获取所有这些并将其绘制在绑定到渲染器的窗口中。

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SDL_Textures and SDL_Surface

SDL_Textures 和 SDL_Surface

The SDL_Rendererrenders SDL_Texture, which stores the pixel information of one element. It's the new version of SDL_Surfacewhich is much the same. The difference is mostly that SDL_Surfaceis just a structcontaining pixel information, while SDL_Textureis an efficient, driver-specific representation of pixel data.

的SDL_Renderer呈现SDL_Texture，其存储一个元件的像素信息。它的新版本SDL_Surface几乎相同。不同之处主要在于SDL_Surface仅struct包含像素信息，而SDL_Texture像素数据的有效、特定于驱动程序的表示。

You can convert an SDL_Surface* to SDL_Texture using

您可以使用将 SDL_Surface* 转换为 SDL_Texture

SDL_Texture* SDL_CreateTextureFromSurface(SDL_Renderer* renderer,
                                          SDL_Surface*  surface)

After this, the SDL_Surface should be freed using

在此之后，应该使用释放 SDL_Surface

SDL_FreeSurface( SDL_Surface* surface )

Another important difference is that SDL_Surfaceuses software rendering (via CPU) while SDL_Textureuses hardware rendering (via GPU).

另一个重要的区别是SDL_Surface使用软件渲染（通过 CPU）而SDL_Texture使用硬件渲染（通过 GPU）。

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SDL_Rect

SDL_矩形

The simplest struct in SDL. It contains only four shorts. x, ywhich holds the position and w, hwhich holds width and height.

SDL 中最简单的结构。它只包含四条短裤。x, y持有位置w, h，持有宽度和高度。

It's important to note that 0, 0is the upper-left corner in SDL. So a higher y-value means lower, and the bottom-right corner will have the coordinate x + w, y + h

需要注意的0, 0是 SDL 中的左上角。所以更高的 -y值意味着更低，并且右下角将有坐标x + w, y + h

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You can read more about SDL2 on my blog.

您可以在我的博客上阅读有关 SDL2 的更多信息。

回答by woolstar

Think of SDL_Windowas physical pixels, and SDL_Rendererand a place to store settings/context.

将其SDL_Window视为物理像素，以及SDL_Renderer存储设置/上下文的位置。

So you create a bunch of resources, and hang them off of the renderer; and then when its ready, you tell renderer to put it all together and send the results to the window.

所以你创建了一堆资源，并将它们挂在渲染器上；然后当它准备好时，你告诉渲染器把它放在一起并将结果发送到窗口。