How to render text in SDL2?

问题:

I was wondering how to render text with SDL2. I found an API called SDL_TTF and some tutorials, however they do not work with my situation.

I'm using an SDL_Window and SDL_Renderer, whereas the tutorials are specific to SDL_Surface.

Is it possible to use SDL_TTF with SDL_Render/SDL_Window? If so, how?

回答1:

Yep, it is possible, given that you have a renderer and a window plus you don't really have any thoughts on dabbling with surfaces then you might want to mind on creating texture, here is a sample code

TTF_Font* Sans = TTF_OpenFont("Sans.ttf", 24); //this opens a font style and sets a size

SDL_Color White = {255, 255, 255};  // this is the color in rgb format, maxing out all would give you the color white, and it will be your text's color

SDL_Surface* surfaceMessage = TTF_RenderText_Solid(Sans, "put your text here", White); // as TTF_RenderText_Solid could only be used on SDL_Surface then you have to create the surface first

SDL_Texture* Message = SDL_CreateTextureFromSurface(renderer, surfaceMessage); //now you can convert it into a texture

SDL_Rect Message_rect; //create a rect
Message_rect.x = 0;  //controls the rect's x coordinate 
Message_rect.y = 0; // controls the rect's y coordinte
Message_rect.w = 100; // controls the width of the rect
Message_rect.h = 100; // controls the height of the rect

//Mind you that (0,0) is on the top left of the window/screen, think a rect as the text's box, that way it would be very simple to understance

//Now since it's a texture, you have to put RenderCopy in your game loop area, the area where the whole code executes

SDL_RenderCopy(renderer, Message, NULL, &Message_rect); //you put the renderer's name first, the Message, the crop size(you can ignore this if you don't want to dabble with cropping), and the rect which is the size and coordinate of your texture

//Don't forget too free your surface and texture

I tried to explain the code line by line, you don't see any window right there since I already assumed that you knew how to initialize a renderer which would give me an idea that you also know how to initialize a window, then all you need is the idea on how to initialize a texture.

Minor questions here, did your window open? was it colored black? if so then my thoughts were right, if not, then you can just ask me and I could change this code to implement the whole section which consists of a renderer and a window.

回答2:

SDL_ttf minimal runnable example

Not super efficient, but easy to integrate. For efficiency see: How to render fonts and text with SDL2 efficiently?

Kept in a separate repo than the main SDL source, but hosted on the same official server, so should be fine: http://hg.libsdl.org/SDL_ttf/

Newlines won't work. You have to work with line heights.

Compile and run:

sudo apt-get install -y libsdl2-dev
gcc -lSDL2 -lSDL2_ttf -o ttf ttf.c
./ttf /usr/share/fonts/truetype/freefont/FreeMonoOblique.ttf

You must pass the path of a TTF font file to the program.

ttf.c

#include <stdlib.h>

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

#define WINDOW_WIDTH 300
#define WINDOW_HEIGHT (WINDOW_WIDTH)

/*
- x, y: upper left corner.
- texture, rect: outputs.
*/
void get_text_and_rect(SDL_Renderer *renderer, int x, int y, char *text,
        TTF_Font *font, SDL_Texture **texture, SDL_Rect *rect) {
    int text_width;
    int text_height;
    SDL_Surface *surface;
    SDL_Color textColor = {255, 255, 255, 0};

    surface = TTF_RenderText_Solid(font, text, textColor);
    *texture = SDL_CreateTextureFromSurface(renderer, surface);
    text_width = surface->w;
    text_height = surface->h;
    SDL_FreeSurface(surface);
    rect->x = x;
    rect->y = y;
    rect->w = text_width;
    rect->h = text_height;
}

int main(int argc, char **argv) {
    SDL_Event event;
    SDL_Rect rect1, rect2;
    SDL_Renderer *renderer;
    SDL_Texture *texture1, *texture2;
    SDL_Window *window;
    char *font_path;
    int quit;

    if (argc == 1) {
        font_path = "FreeSans.ttf";
    } else if (argc == 2) {
        font_path = argv[1];
    } else {
        fprintf(stderr, "error: too many arguments\n");
        exit(EXIT_FAILURE);
    }

    /* Inint TTF. */
    SDL_Init(SDL_INIT_TIMER | SDL_INIT_VIDEO);
    SDL_CreateWindowAndRenderer(WINDOW_WIDTH, WINDOW_WIDTH, 0, &window, &renderer);
    TTF_Init();
    TTF_Font *font = TTF_OpenFont(font_path, 24);
    if (font == NULL) {
        fprintf(stderr, "error: font not found\n");
        exit(EXIT_FAILURE);
    }
    get_text_and_rect(renderer, 0, 0, "hello", font, &texture1, &rect1);
    get_text_and_rect(renderer, 0, rect1.y + rect1.h, "world", font, &texture2, &rect2);

    quit = 0;
    while (!quit) {
        while (SDL_PollEvent(&event) == 1) {
            if (event.type == SDL_QUIT) {
                quit = 1;
            }
        }
        SDL_SetRenderDrawColor(renderer, 0, 0, 0, 0);
        SDL_RenderClear(renderer);

        /* Use TTF textures. */
        SDL_RenderCopy(renderer, texture1, NULL, &rect1);
        SDL_RenderCopy(renderer, texture2, NULL, &rect2);

        SDL_RenderPresent(renderer);
    }

    /* Deinit TTF. */
    SDL_DestroyTexture(texture1);
    SDL_DestroyTexture(texture2);
    TTF_Quit();

    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(window);
    SDL_Quit();
    return EXIT_SUCCESS;
}

GitHub upstream.

Tested in Ubuntu 16.04, SDL 2.0.4.

回答3:

Yes it is. You create a surface with the text you want and then convert it to a texture that you can render.

Some sample code from one of my projects:

std::string score_text = "score: " + std::to_string(score);        
SDL_Color textColor = { 255, 255, 255, 0 };
SDL_Surface* textSurface = TTF_RenderText_Solid(font, score_text.c_str(), textColor);
SDL_Texture* text = SDL_CreateTextureFromSurface(renderer, textSurface);
int text_width = textSurface->w;
int text_height = textSurface->h;
SDL_FreeSurface(textSurface);
SDL_Rect renderQuad = { 20, win_height - 30, text_width, text_height };
SDL_RenderCopy(renderer, text, NULL, &renderQuad);
SDL_DestroyTexture(text);

This assumes you've properly initialized SDL_ttf and loaded a font. In the example scoreis an int. The screen gets cleared and rendered to somewhere else (I didn't include that part).

For a full working example, check out the tutorial for SDL_ttf in SDL2 at Lazy Foo.