canvas - c++ SDL - Render inside a window's particular area -

i want align game components html game.

my sdl_windowwill have sdl_rendererrendering of components. these components buttons, images , rectangle area like html canvas.

i want game rendered inside canvas, because implement "world" , "camera" affect "canvas", while gui around "canvas" rendered independently of camera.

how have renderer rendering particular area inside of window?

i can't mathematics, because want every texture rendered inside canvas, far point of view, hidden.

part of code:

    sdl_window* gwindow = sdl_createwindow("title", sdl_windowpos_undefined, sdl_windowpos_undefined, 800, 600, sdl_window_shown);     sdl_renderer* grenderer = sdl_createrenderer(gwindow, -1, sdl_renderer_accelerated);      while (true) {         sdl_renderclear(grenderer);         render_gui(); // can part         render_game_inside_canvas(); // ?         sdl_renderpresent(grenderer);     } 

you can glviewport() call this:

point2d pos = get_pos(); vector2d sz = get_size(); glviewport(pos.x, screen_height-pos.y-sz.dy, sz.dx, sz.dy); obj.render(); glviewport(0,0,screen_width, screen_height); 

it kinda requires know dimensions of whole screen... (the odd calculation required because glviewport keeps screen upsidedown :-)