examples: Much, much easier way to generate thumbnail and onmouseover files.

examples/README.md

@@ -69,34 +69,26 @@ everything consistent. You can ignore it.
 
 (Since I have to figure this out every time.)
 
-This is how Ryan is doing it currently, although this could be automated
-_much_ better:
+This is how Ryan is doing it currently.
 
-- Launch the example app on Desktop Linux. Gnome currently always puts it at
-  the same location.
-- Hit PrtScr for capture.
-- Highlight exactly the window without the titlebar. Usually I take an
-  initial screenshot, paste it into Gimp, zoom in and make sure it's
-  pixel-perfect. Repeat. This takes too much effort and should be automated.
-- Take a screenshot for thumbnail.png if it makes sense.
-- Take a video of a few seconds of the example app running.
-- Take the video and turn it into webp format:
+- `rm -f frame*.bmp`
+- Temporarily add `#include "../../save-rendering-to-bitmaps.h"` after any SDL
+  includes in the example program.
+- Launch the example app, interact with it, let it run for a few seconds, quit.
+- This will dump a "frameX.bmp" file for each frame rendered.
+- Make a video in webp format from the bitmaps (this assumes the bitmaps were
+  stored at 60fps, you might have to tweak).
 
   ```bash
-  ffmpeg -i video.mp4 -loop 0 -quality 40 -framerate 10 -frames:v 40 onmouseover.webp
+  ffmpeg -framerate 60 -pattern_type glob -i 'frame*.bmp' -loop 0 -quality 40 -r 10 -frames:v 40 onmouseover.webp
   ```
 
   You might need to start in the middle of the video, or mess with quality or
   number of frames to generate, ymmv.
-- If you didn't take a screenshot for the thumbnail, extract a frame from the
-  video. The 0 means "the first frame of the video" but you can choose another:
+- Pick a frame for the thumbnail, make it a .png, and run that png through
+  pngquant for massive file size reduction without any obvious loss in quality:
 
   ```bash
-  ffmpeg -i video.mp4 -vf "select=eq(n\,0)" thumbnail.png
+  convert frame00000.bmp cvt.png ; pngquant cvt.png --output thumbnail.png ; rm -f cvt.png
   ```
-- Run the thumbnail through pngquant for massive file size reduction without
-  any obvious loss in quality:
 
-  ```bash
-  pngquant thumbnail.png --output new_thumbnail.png
-  ```

examples/save-rendering-to-bitmaps.h

@@ -0,0 +1,49 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2025 Sam Lantinga <slouken@libsdl.org>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+
+/*
+This is for generating thumbnails and videos of examples. Just include it
+temporarily and let it override SDL_RenderPresent, etc, and it'll dump each
+frame rendered to a new .bmp file.
+*/
+
+static bool SAVERENDERING_SDL_RenderPresent(SDL_Renderer *renderer)
+{
+    static unsigned int framenum = 0;
+    SDL_Surface *surface = SDL_RenderReadPixels(renderer, NULL);
+    if (!surface) {
+        SDL_LogError(SDL_LOG_CATEGORY_RENDER, "Failed to read pixels for frame #%u! (%s)", framenum, SDL_GetError());
+    } else {
+        char fname[64];
+        SDL_snprintf(fname, sizeof (fname), "frame%05u.bmp", framenum);
+        if (!SDL_SaveBMP(surface, fname)) {
+            SDL_LogError(SDL_LOG_CATEGORY_RENDER, "Failed to save bmp for frame #%u! (%s)", framenum, SDL_GetError());
+        }
+        SDL_DestroySurface(surface);
+    }
+
+    framenum++;
+
+    return SDL_RenderPresent(renderer);
+}
+
+#define SDL_RenderPresent SAVERENDERING_SDL_RenderPresent
+