如何在SDL2中呈现文本？

Question

我想知道如何使用SDL2渲染文本。我找到了一个名为SDL_TTF的API和一些教程，但是它们不适用于我的情况。

我正在使用SDL_Window和SDL_Renderer，而教程是特定于SDL_Surface。

有可能使用SDL_TTF与SDL_Render/SDL_Window？如果是这样，怎么样？

Answer 1

是的，有可能，鉴于你有一个渲染器和一个窗口加上你真的没有任何关于涉及表面的想法，那么你可能想要创建纹理，这里是一个示例代码

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

我试图逐行解释代码，你没有看到任何窗口，因为我已经假设你知道如何初始化渲染器，这会让我知道你也知道如何初始化一个窗口，然后你需要的是如何初始化纹理的想法。

这里有一些小问题，你的窗户打开了吗？它是黑色的吗？如果是这样，那么我的想法是正确的，如果没有，那么你可以问我，我可以改变这个代码来实现整个部分，包括一个渲染器和一个窗口。

Answer 2

SDL_ttf最小可运行示例

不是超级高效，但易于集成。为了效率，请参阅：How to render fonts and text with SDL2 efficiently?

保存在一个单独的repo而不是主SDL源，但托管在同一个官方服务器上，所以应该没问题：http://hg.libsdl.org/SDL_ttf/

换行不起作用。你必须使用线高。

编译并运行：

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

您必须将TTF字体文件的路径传递给该程序。

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。

在Ubuntu 16.04，SDL 2.0.4中测试。

Answer 3

是的。使用所需文本创建曲面，然后将其转换为可以渲染的纹理。

我的一个项目的一些示例代码：

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);

这假设您已正确初始化SDL_ttf并加载了字体。在示例中，score是一个int。屏幕被清除并呈现给其他地方（我没有包括那部分）。

有关完整的工作示例，请查看tutorial for SDL_ttf in SDL2 at Lazy Foo。