Automatically generate screenshots for all examples (#2379)

examples/screenshot/Cargo.toml

@@ -9,6 +9,8 @@ publish = false
 
 
 [dependencies]
-eframe = { path = "../../crates/eframe" }
+eframe = { path = "../../crates/eframe", features = [
+    "__screenshot", # __screenshot is so we can dump a ascreenshot using EFRAME_SCREENSHOT_TO
+] }
 egui_extras = { path = "../../crates/egui_extras", features = ["image"] }
 itertools = "0.10.3"

examples/screenshot/README.md

@@ -1,3 +1,7 @@
+Example how to take screenshots and display them with eframe/egui.
+
 ```sh
 cargo run -p screenshot
 ```
+
+![](screenshot.png)

examples/screenshot/src/main.rs

@@ -74,23 +74,25 @@ impl eframe::App for MyApp {
 
         self.take_screenshot = false;
         if let Some(gl) = frame.gl() {
-            let mut buf = vec![0u8; screen_size_px[0] as usize * screen_size_px[1] as usize * 4];
+            let [w, h] = screen_size_px;
+            let mut buf = vec![0u8; w as usize * h as usize * 4];
             let pixels = glow::PixelPackData::Slice(&mut buf[..]);
             unsafe {
                 gl.read_pixels(
                     0,
                     0,
-                    screen_size_px[0] as i32,
-                    screen_size_px[1] as i32,
+                    w as i32,
+                    h as i32,
                     glow::RGBA,
                     glow::UNSIGNED_BYTE,
                     pixels,
                 );
             }
 
+            // Flip vertically:
             let mut rows: Vec<Vec<u8>> = buf
                 .into_iter()
-                .chunks(screen_size_px[0] as usize * 4)
+                .chunks(w as usize * 4)
                 .into_iter()
                 .map(|chunk| chunk.collect())
                 .collect();