SDL渲染为新纹理

Question

I'm making a 2d game with SDL library.

I'm trying to draw the map for each frame over and over again, because I'm moving the map, according to the player's movement to achieve illusion that the camera follows the player.

So basically, if the player moves, I'm moving all the blocks ( those two , player movement and update blocks positions , are handled in a separate thread ) and rendering the map texture over again , in the main thread.

Although, it is really not efficient to draw all the blocks each frame, and it lags the window rendering, so what I want to do is to make another thread, that will create a blank texture that the blocks could be rendered there.

The question is : Is it possible to do so without a renderer ? to draw all the blocks to a new texture without actually stuck the main renderer that draws the window and prevent it from going over all the blocks each frame ?

This is the code that goes throgh the map blocks and drawing them to a new texture :

SDL_Texture* GraphicsDrawer::drawMap() {
    map = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_ARGB8888, SDL_TEXTUREACCESS_TARGET, WINDOW_WIDTH, WINDOW_HEIGHT);
    SDL_SetTextureBlendMode(map, SDL_BLENDMODE_BLEND); // set texture to be transparent
    SDL_SetRenderTarget(renderer, map);
    for (Block block : blocks) {
        std::cout << block.getTexture() << std::endl;
        SDL_RenderCopy(renderer, block.getTexture(), NULL, &block.getPosition());
        SDL_RenderPresent(renderer);
    }
    SDL_SetRenderTarget(renderer, NULL);
    return map;
}

This is the code that draws textures to the window :

void Game::render() {
    SDL_RenderClear(renderer);
    //map
    SDL_RenderCopy(renderer, map, NULL, NULL);
    //player
    SDL_RenderCopy(renderer, player->getAnimation(player->getFlipImageFlag()), NULL, &player->getPosition());

    SDL_SetRenderDrawColor(renderer, BG_R, BG_G, BG_B, BG_A);
    SDL_RenderPresent(renderer);
}

Answer 1

If I understand what you're asking, you'd want to update only SOME blocks/tiles on the map at each time? That's not possible unless you divide your map texture into pieces, which could create more overhead than you're saving. You can't SDL_RenderClear only part of a texture without some potentially undesired side effects.

What I would do is break the map texture up into layers (map_floors, map_walls, etc.) and cache each layer. So instead of calling GraphicsDrawer::drawMap() every frame, only call it on frames in which a layer changes. So if a NPC moves, only redraw the layer which has NPC's on it. You'd still call SDL_RenderCopy() every frame but the texture for each layer doesn't have to be regenerated every frame.