From 6aaedb813fa11ba0679c3051bc2eb28646b9506c Mon Sep 17 00:00:00 2001 From: 3gg <3gg@shellblade.net> Date: Sat, 30 Aug 2025 16:53:58 -0700 Subject: Update to SDL3 --- .../examples/renderer/17-read-pixels/read-pixels.c | 178 +++++++++++++++++++++ 1 file changed, 178 insertions(+) create mode 100644 src/contrib/SDL-3.2.20/examples/renderer/17-read-pixels/read-pixels.c (limited to 'src/contrib/SDL-3.2.20/examples/renderer/17-read-pixels/read-pixels.c') diff --git a/src/contrib/SDL-3.2.20/examples/renderer/17-read-pixels/read-pixels.c b/src/contrib/SDL-3.2.20/examples/renderer/17-read-pixels/read-pixels.c new file mode 100644 index 0000000..556b490 --- /dev/null +++ b/src/contrib/SDL-3.2.20/examples/renderer/17-read-pixels/read-pixels.c @@ -0,0 +1,178 @@ +/* + * This example creates an SDL window and renderer, and draws a + * rotating texture to it, reads back the rendered pixels, converts them to + * black and white, and then draws the converted image to a corner of the + * screen. + * + * This isn't necessarily an efficient thing to do--in real life one might + * want to do this sort of thing with a render target--but it's just a visual + * example of how to use SDL_RenderReadPixels(). + * + * This code is public domain. Feel free to use it for any purpose! + */ + +#define SDL_MAIN_USE_CALLBACKS 1 /* use the callbacks instead of main() */ +#include +#include + +/* We will use this renderer to draw into this window every frame. */ +static SDL_Window *window = NULL; +static SDL_Renderer *renderer = NULL; +static SDL_Texture *texture = NULL; +static int texture_width = 0; +static int texture_height = 0; +static SDL_Texture *converted_texture = NULL; +static int converted_texture_width = 0; +static int converted_texture_height = 0; + +#define WINDOW_WIDTH 640 +#define WINDOW_HEIGHT 480 + +/* This function runs once at startup. */ +SDL_AppResult SDL_AppInit(void **appstate, int argc, char *argv[]) +{ + SDL_Surface *surface = NULL; + char *bmp_path = NULL; + + SDL_SetAppMetadata("Example Renderer Read Pixels", "1.0", "com.example.renderer-read-pixels"); + + if (!SDL_Init(SDL_INIT_VIDEO)) { + SDL_Log("Couldn't initialize SDL: %s", SDL_GetError()); + return SDL_APP_FAILURE; + } + + if (!SDL_CreateWindowAndRenderer("examples/renderer/read-pixels", WINDOW_WIDTH, WINDOW_HEIGHT, 0, &window, &renderer)) { + SDL_Log("Couldn't create window/renderer: %s", SDL_GetError()); + return SDL_APP_FAILURE; + } + + /* Textures are pixel data that we upload to the video hardware for fast drawing. Lots of 2D + engines refer to these as "sprites." We'll do a static texture (upload once, draw many + times) with data from a bitmap file. */ + + /* SDL_Surface is pixel data the CPU can access. SDL_Texture is pixel data the GPU can access. + Load a .bmp into a surface, move it to a texture from there. */ + SDL_asprintf(&bmp_path, "%ssample.bmp", SDL_GetBasePath()); /* allocate a string of the full file path */ + surface = SDL_LoadBMP(bmp_path); + if (!surface) { + SDL_Log("Couldn't load bitmap: %s", SDL_GetError()); + return SDL_APP_FAILURE; + } + + SDL_free(bmp_path); /* done with this, the file is loaded. */ + + texture_width = surface->w; + texture_height = surface->h; + + texture = SDL_CreateTextureFromSurface(renderer, surface); + if (!texture) { + SDL_Log("Couldn't create static texture: %s", SDL_GetError()); + return SDL_APP_FAILURE; + } + + SDL_DestroySurface(surface); /* done with this, the texture has a copy of the pixels now. */ + + return SDL_APP_CONTINUE; /* carry on with the program! */ +} + +/* This function runs when a new event (mouse input, keypresses, etc) occurs. */ +SDL_AppResult SDL_AppEvent(void *appstate, SDL_Event *event) +{ + if (event->type == SDL_EVENT_QUIT) { + return SDL_APP_SUCCESS; /* end the program, reporting success to the OS. */ + } + return SDL_APP_CONTINUE; /* carry on with the program! */ +} + +/* This function runs once per frame, and is the heart of the program. */ +SDL_AppResult SDL_AppIterate(void *appstate) +{ + const Uint64 now = SDL_GetTicks(); + SDL_Surface *surface; + SDL_FPoint center; + SDL_FRect dst_rect; + + /* we'll have a texture rotate around over 2 seconds (2000 milliseconds). 360 degrees in a circle! */ + const float rotation = (((float) ((int) (now % 2000))) / 2000.0f) * 360.0f; + + /* as you can see from this, rendering draws over whatever was drawn before it. */ + SDL_SetRenderDrawColor(renderer, 0, 0, 0, SDL_ALPHA_OPAQUE); /* black, full alpha */ + SDL_RenderClear(renderer); /* start with a blank canvas. */ + + /* Center this one, and draw it with some rotation so it spins! */ + dst_rect.x = ((float) (WINDOW_WIDTH - texture_width)) / 2.0f; + dst_rect.y = ((float) (WINDOW_HEIGHT - texture_height)) / 2.0f; + dst_rect.w = (float) texture_width; + dst_rect.h = (float) texture_height; + /* rotate it around the center of the texture; you can rotate it from a different point, too! */ + center.x = texture_width / 2.0f; + center.y = texture_height / 2.0f; + SDL_RenderTextureRotated(renderer, texture, NULL, &dst_rect, rotation, ¢er, SDL_FLIP_NONE); + + /* this next whole thing is _super_ expensive. Seriously, don't do this in real life. */ + + /* Download the pixels of what has just been rendered. This has to wait for the GPU to finish rendering it and everything before it, + and then make an expensive copy from the GPU to system RAM! */ + surface = SDL_RenderReadPixels(renderer, NULL); + + /* This is also expensive, but easier: convert the pixels to a format we want. */ + if (surface && (surface->format != SDL_PIXELFORMAT_RGBA8888) && (surface->format != SDL_PIXELFORMAT_BGRA8888)) { + SDL_Surface *converted = SDL_ConvertSurface(surface, SDL_PIXELFORMAT_RGBA8888); + SDL_DestroySurface(surface); + surface = converted; + } + + if (surface) { + /* Rebuild converted_texture if the dimensions have changed (window resized, etc). */ + if ((surface->w != converted_texture_width) || (surface->h != converted_texture_height)) { + SDL_DestroyTexture(converted_texture); + converted_texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_RGBA8888, SDL_TEXTUREACCESS_STREAMING, surface->w, surface->h); + if (!converted_texture) { + SDL_Log("Couldn't (re)create conversion texture: %s", SDL_GetError()); + return SDL_APP_FAILURE; + } + converted_texture_width = surface->w; + converted_texture_height = surface->h; + } + + /* Turn each pixel into either black or white. This is a lousy technique but it works here. + In real life, something like Floyd-Steinberg dithering might work + better: https://en.wikipedia.org/wiki/Floyd%E2%80%93Steinberg_dithering*/ + int x, y; + for (y = 0; y < surface->h; y++) { + Uint32 *pixels = (Uint32 *) (((Uint8 *) surface->pixels) + (y * surface->pitch)); + for (x = 0; x < surface->w; x++) { + Uint8 *p = (Uint8 *) (&pixels[x]); + const Uint32 average = (((Uint32) p[1]) + ((Uint32) p[2]) + ((Uint32) p[3])) / 3; + if (average == 0) { + p[0] = p[3] = 0xFF; p[1] = p[2] = 0; /* make pure black pixels red. */ + } else { + p[1] = p[2] = p[3] = (average > 50) ? 0xFF : 0x00; /* make everything else either black or white. */ + } + } + } + + /* upload the processed pixels back into a texture. */ + SDL_UpdateTexture(converted_texture, NULL, surface->pixels, surface->pitch); + SDL_DestroySurface(surface); + + /* draw the texture to the top-left of the screen. */ + dst_rect.x = dst_rect.y = 0.0f; + dst_rect.w = ((float) WINDOW_WIDTH) / 4.0f; + dst_rect.h = ((float) WINDOW_HEIGHT) / 4.0f; + SDL_RenderTexture(renderer, converted_texture, NULL, &dst_rect); + } + + SDL_RenderPresent(renderer); /* put it all on the screen! */ + + return SDL_APP_CONTINUE; /* carry on with the program! */ +} + +/* This function runs once at shutdown. */ +void SDL_AppQuit(void *appstate, SDL_AppResult result) +{ + SDL_DestroyTexture(converted_texture); + SDL_DestroyTexture(texture); + /* SDL will clean up the window/renderer for us. */ +} + -- cgit v1.2.3