inverting the control, so the browser controls the main loop.

this gives the browser a chance to render the frames.

Author: diekmann

Diff for: doom/README.md

@@ -110,4 +110,12 @@ But using git tag `llvmorg-11.1.0`.
 
 Dat feel! After so much theory and no way to test. Finally seeing the first screen of doom rendered. Awesome!
 
-![Doom rendering the first screen to an HTML5 canvas](imgs/doom_first_screen_renders_to_canvas.png)
+![Doom rendering the first screen to an HTML5 canvas](imgs/doom_first_screen_renders_to_canvas.png)
+
+---
+
+If I don't make `I_FinishUpdate` `panic!()`, then doom runs in its infinite game loop.
+Unfortunately, this runs at 100% CPU, firefox complains that a website is misbehaving, and nothing is rendered, since the browser has no chance of drawing the animation.
+
+Probably, I want to change doom such that doom itself is not looping, but I can call the loop via `window.requestAnimationFrame()`.
+This somehow inverses control and gives the browser a chance to render the frames.

Diff for: doom/index.html

@@ -59,6 +59,12 @@
       WebAssembly.instantiateStreaming(fetch('target/wasm32-unknown-unknown/debug/doom.wasm'), importObject)
       .then(obj => {
         obj.instance.exports.main();
+
+        function step(timestamp) {
+          obj.instance.exports.doom_loop_step();
+          window.requestAnimationFrame(step);
+        }
+        window.requestAnimationFrame(step);
       });
     </script>
   </body>

Diff for: doom/linuxdoom-1.10/d_main.c

@@ -351,7 +351,7 @@ void D_Display (void)
 //
 extern  boolean         demorecording;
 
-void D_DoomLoop (void)
+void D_DoomLoop_prepare (void)
 {
     if (demorecording)
 	G_BeginRecording ();
@@ -365,9 +365,10 @@ void D_DoomLoop (void)
     }
 
     I_InitGraphics ();
+}
 
-    while (1)
-    {
+
+void D_DoomLoop_loop (void) {
 	// frame syncronous IO operations
 	I_StartFrame ();                
 
@@ -403,7 +404,13 @@ void D_DoomLoop (void)
 	// Update sound output.
 	I_SubmitSound();
 #endif
-    }
+}
+
+void D_DoomLoop (void) { // TODO: remove!!
+	D_DoomLoop_prepare();
+	while(1){
+		D_DoomLoop_loop();
+	}
 }
 
 
@@ -1170,5 +1177,6 @@ void D_DoomMain (void)
 
     }
 
-    D_DoomLoop ();  // never returns
+    //D_DoomLoop ();  // never returns // inversion of control, browser controls the loop.
+	D_DoomLoop_prepare();
 }

Diff for: doom/src/main.rs

@@ -8,7 +8,8 @@ pub type c_long_double = ::std::os::raw::c_double; //?
 // C libraries
 extern "C" {
     // d_main.c
-    fn D_DoomMain() -> !;
+    fn D_DoomMain();
+    fn D_DoomLoop_loop();
 
     // m_argv.c
     static mut myargc: c_int;
@@ -90,3 +91,8 @@ fn main() {
         D_DoomMain();
     };
 }
+
+#[no_mangle]
+pub extern "C" fn doom_loop_step() {
+    unsafe { D_DoomLoop_loop() };
+}

Diff for: doom/src/video.rs

@@ -352,7 +352,7 @@ extern "C" fn I_FinishUpdate() {
     unsafe {
         js_draw_screen(canvas.as_ptr());
     }
-    panic!("I_FinishUpdate unimplemented");
+    crate::log!("I_FinishUpdate");
 }
 
 #[no_mangle]