SDL3 framebuffer.c

//
// drop in to sdl3_template for a fixed framebuffer experience
//
#include <SDL3/SDL.h>
#include <SDL3/SDL_main.h>
#include <SDL3/SDL_stdinc.h>
#include <math.h>

//  "game" size
#define APP_WIDTH 384
#define APP_HEIGHT 216

//  see SDL_pixels.h for options 
#define APP_PIXEL_FORMAT SDL_PIXELFORMAT_XRGB4444
//  bytes per pixel 
#define APP_PIXEL_SIZE 2

//  test function to draw a pixel
void plot(Sint16 x, Sint16 y, Uint32 c);

struct {
    SDL_Window*     window;
    SDL_Renderer*   renderer;
    SDL_Texture*    fb_texture;
    SDL_bool        app_quit;
    void           *buffer;
}AppContext;

int SDL_Fail(){
    SDL_LogError(SDL_LOG_CATEGORY_CUSTOM, "Error %s", SDL_GetError());
    return -1;
}

int SDL_AppInit(void** appstate, int argc, char* argv[])
{
    memset(&AppContext, 0, sizeof(AppContext));
    AppContext.app_quit = SDL_FALSE;
    // init the library, here we make a window so we only need the Video capabilities.
    if (SDL_Init(SDL_INIT_VIDEO)){
        return SDL_Fail();
    }
    // create a window
    AppContext.window = SDL_CreateWindow("Window", APP_WIDTH, APP_HEIGHT, SDL_WINDOW_RESIZABLE);
    if (!AppContext.window){
        return SDL_Fail();
    }
    
    AppContext.renderer = SDL_CreateRenderer(AppContext.window, NULL);
    if (!AppContext.renderer){
        return SDL_Fail();
    }

    //  create texture the same format and size as the "game"
  
    AppContext.fb_texture = SDL_CreateTexture(AppContext.renderer, APP_PIXEL_FORMAT, SDL_TEXTUREACCESS_STREAMING, APP_WIDTH, APP_HEIGHT);

    //  create a raw pixel buffer the same
  
    AppContext.buffer = (void*)SDL_calloc(APP_PIXEL_SIZE,APP_WIDTH * APP_HEIGHT );
    if (!AppContext.buffer) {
        return SDL_Fail();
    }

    // print some information about the window
    SDL_ShowWindow(AppContext.window);
    {
        int width, height, bbwidth, bbheight;
        SDL_GetWindowSize(AppContext.window, &width, &height);
        SDL_GetWindowSizeInPixels(AppContext.window, &bbwidth, &bbheight);
        SDL_Log("Window size: %ix%i", width, height);
        SDL_Log("Backbuffer size: %ix%i", bbwidth, bbheight);
        if (width != bbwidth){
            SDL_Log("This is a highdpi environment.");
        }
    }

    SDL_Log("Application started successfully!");
    //  handles resize of window, includes black borders
    //  currently uses NEAREST filter
    SDL_SetRenderLogicalPresentation(AppContext.renderer, APP_WIDTH, APP_HEIGHT, SDL_LOGICAL_PRESENTATION_LETTERBOX, SDL_SCALEMODE_NEAREST);    

    return 0;
}

int SDL_AppEvent(void *appstate, const SDL_Event* event)
{
    if (event->type == SDL_EVENT_QUIT)
    {
        AppContext.app_quit = SDL_TRUE;
    }

    return 0;
}

int SDL_AppIterate(void *appstate)
{
    //  convert mouse to "game" coordinates
    float mx,my;
    SDL_GetMouseState(&mx,&my);
    SDL_RenderCoordinatesFromWindow(AppContext.renderer,mx,my,&mx,&my);

    plot((int)mx, (int)my, 0xffff);

    //  random doodle
    Uint16 x = rand() % APP_WIDTH;
    Uint16 y = rand() % APP_HEIGHT;

    plot(x, y, rand());

    SDL_RenderClear(AppContext.renderer);

    //  copy raw buffer to texture
    SDL_UpdateTexture(AppContext.fb_texture, NULL, AppContext.buffer, APP_WIDTH * APP_PIXEL_SIZE);
    //  draw it
    SDL_RenderTexture(AppContext.renderer, AppContext.fb_texture, NULL, NULL);

    SDL_RenderPresent(AppContext.renderer);

    return AppContext.app_quit;
}

void SDL_AppQuit(void* appstate)
{
    SDL_free(AppContext.buffer);
    SDL_DestroyTexture(AppContext.fb_texture);
    SDL_DestroyRenderer(AppContext.renderer);
    SDL_DestroyWindow(AppContext.window);
    SDL_Quit();
    SDL_Log("Application quit successfully!");
}

void plot(Sint16 x, Sint16 y, Uint32 c)
{
    if ((x < APP_WIDTH) && (y < APP_HEIGHT))
    {
#if (APP_PIXEL_SIZE == 1)
        Uint8* ptr = (Uint8*)AppContext.buffer;
        ptr[x + (y * APP_WIDTH)] = (Uint8)c;
#endif
#if APP_PIXEL_SIZE == 2
        Uint16* ptr = (Uint16*)AppContext.buffer;
        ptr[x + (y * APP_WIDTH)] = (Uint16)c;
#endif
#if APP_PIXEL_SIZE == 4
        Uint32* ptr = (Uint32*)AppContext.buffer;
        ptr[x + (y * APP_WIDTH)] = (Uint32)c;
#endif
    }
}