What is an SDL renderer?

Question

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

What is it? What does it do? What\'s the difference between SDL_Rendere

Answer 1

SDL_Window

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

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SDL_Renderer

SDL_Renderer is a struct that handles all rendering. It is tied to a SDL_Window so 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_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_Texture and 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_Rect is 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.

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SDL_Textures and SDL_Surface

The SDL_Renderer renders SDL_Texture, which stores the pixel information of one element. It's the new version of SDL_Surface which is much the same. The difference is mostly that SDL_Surface is just a struct containing pixel information, while SDL_Texture is an efficient, driver-specific representation of pixel data.

You can convert an SDL_Surface* to SDL_Texture using

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

After this, the SDL_Surface should be freed using

SDL_FreeSurface( SDL_Surface* surface )

Another important difference is that SDL_Surface uses software rendering (via CPU) while SDL_Texture uses hardware rendering (via GPU).

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SDL_Rect

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

It's important to note that 0, 0 is 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

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You can read more about SDL2 on my blog.

Answer 2

Think of SDL_Window as physical pixels, and SDL_Renderer and a place to store settings/context.

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.