SDL - Update Surface in C - c

Question

i use SDL Lib and SDL_TTF Lib
I have a code that allows you to enter text
And then display the text on my window
so here the code
TTF_Init();
SDL_Init(SDL_INIT_VIDEO);
TTF_Font * font = TTF_OpenFont("C:\\Windows\\Fonts\\Arial.ttf", 25);
SDL_Color color = { 255, 255, 255 };
SDL_Surface * surface = TTF_RenderText_Solid(font,"", color);
SDL_Window * window = SDL_CreateWindow("SDL_ttf in SDL2",
SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 640,
480, 0);
SDL_Renderer * renderer = SDL_CreateRenderer(window, -1, 0);
SDL_Texture * texture = SDL_CreateTextureFromSurface(renderer, surface);
int texW = 200;
int texH = 200;
SDL_QueryTexture(texture, NULL, NULL, &texW, &texH);
SDL_Rect dstrect = { 200, 200, texW, texH };
SDL_RenderCopy(renderer, texture, NULL, &dstrect);
SDL_RenderPresent(renderer);
while (program_launched)
{
SDL_bool has_type = SDL_FALSE;
SDL_WaitEvent(&event);
if(event.type == SDL_QUIT)
program_launched = SDL_FALSE;
else if( event.type == SDL_KEYDOWN)
{
if(event.key.keysym.sym == SDLK_BACKSPACE && len)
{
rep[len - 1] = 0;
len--;
has_type = SDL_TRUE;
}
if(event.key.keysym.sym == SDLK_v && (SDL_GetModState() & KMOD_CTRL) && SDL_HasClipboardText())
{
char *tmp = SDL_GetClipboardText();
size_t l = strlen(tmp);
size_t l_copy = len + l < LEN_MAX ? l : LEN_MAX - len;
strncpy(rep + len, tmp, l_copy);
len += l_copy;
SDL_free(tmp);
has_type = SDL_TRUE;
}
if(event.key.keysym.sym == SDLK_c && (SDL_GetModState() & KMOD_CTRL))
SDL_SetClipboardText(rep);
}
else if(event.type == SDL_TEXTINPUT)
{
size_t l = strlen(event.text.text);
size_t l_copy = len + l < LEN_MAX ? l : LEN_MAX - len;
strncpy(rep + len, event.text.text, l_copy);
len += l_copy;
has_type = SDL_TRUE;
}
if(has_type)
surface = TTF_RenderText_Solid(font,rep, color);
texture = SDL_CreateTextureFromSurface(renderer, surface);
SDL_QueryTexture(texture, NULL, NULL, &texW, &texH);
SDL_Rect dstrect = { 0, 0, texW, texH };
SDL_RenderCopy(renderer, texture, NULL, &dstrect);
SDL_RenderPresent(renderer);
}
It's to (has-type) that I display the buff (rep)
But my problem is here:
I can write and display in the window a text
But if i do a backspace and i write
The texts overlap because the window, at least the rectangle is not updated
Is it possible to delete the content of my window (to display the buff without overlapping) ?
I use this documentation
https://www.libsdl.org/projects/SDL_ttf/docs/SDL_ttf.pdf
I had tried with this function: SDL_UpdateWindowSurface(window);
But nothing helps
Compiler: GCC
OS: Windows

Answer 1

It's because once you've outputed something to the screen, it stays there unless you clear it or put something above it.
Think of it as a painter plotting things on his canvas. If you want to overwrite something, you have to overwrite the previous shape.
The simplest way to deal with this would be to call SDL_RenderClear at the beginning of every draw, it clears the whole screen clean, and then every time you render something it'll never overlap the previous stuff.