[test] Re-instate ability to delay reference image collection. NFC (#22672)

In #22665 I removed the manually_trigger_reftest. However this resulted
in racey behaviour in some tests. It turns out that running `doReftest`
during `postRun` was working, but only because `doReftest` itself was
doing async work, thus delaying the actual capture of the canvas bits.

This change re-instates the behaviour but without the need to test
setting in python.

Author: sbc100

test/browser/test_sdl2_image_prepare.c

@@ -40,6 +40,8 @@ void ready(const char *f) {
   testImage("screenshot.jpg"); // relative path
 
   SDL_RenderPresent(renderer);
+
+  EM_ASM(reftestUnblock());
 }
 
 int main() {
@@ -56,6 +58,7 @@ int main() {
 
   assert(emscripten_run_preload_plugins("screenshot.jpg", ready, NULL) == 0);
 
+  EM_ASM(reftestBlock());
   return 0;
 }
 

test/browser/test_sdl2_image_prepare_data.c

@@ -55,6 +55,8 @@ void ready(void *arg, const char *fileName) {
     free((void*)seenName); // As the API docs say, we are responsible for freeing the 'fake' names we are given
 
     SDL_RenderPresent(renderer);
+
+    EM_ASM(reftestUnblock());
   }
 }
 
@@ -75,6 +77,7 @@ int main() {
   emscripten_run_preload_plugins_data(buffer, SIZE, "jpg", (void*)25, ready, NULL);
   emscripten_run_preload_plugins_data(buffer, SIZE, "jpg", (void*)33, ready, NULL); // twice to see different filenames
 
+  EM_ASM(reftestBlock());
   return 0;
 }
 

test/browser/test_sdl_image_must_prepare.c

@@ -36,6 +36,8 @@ void ready(const char *f) {
   testImage("screenshot.jpg", 1);
 
   SDL_Flip(screen);
+
+  EM_ASM(reftestUnblock());
 }
 
 int main() {
@@ -48,6 +50,7 @@ int main() {
 
   assert(emscripten_run_preload_plugins("screenshot.jpg", ready, NULL) == 0);
 
+  EM_ASM(reftestBlock());
   return 0;
 }
 

test/browser/test_sdl_image_prepare.c

@@ -37,6 +37,8 @@ void ready(const char *f) {
   testImage("screenshot.jpg"); // relative path
 
   SDL_Flip(screen);
+
+  EM_ASM(reftestUnblock());
 }
 
 int main() {
@@ -51,6 +53,7 @@ int main() {
 
   assert(emscripten_run_preload_plugins("screenshot.jpg", ready, NULL) == 0);
 
+  EM_ASM(reftestBlock());
   return 0;
 }
 

test/browser/test_sdl_image_prepare_data.c

@@ -55,6 +55,7 @@ void ready(void *arg, const char *fileName) {
     free((void*)seenName); // As the API docs say, we are responsible for freeing the 'fake' names we are given
 
     SDL_Flip(screen);
+    EM_ASM(reftestUnblock());
   }
 }
 
@@ -73,6 +74,7 @@ int main() {
   emscripten_run_preload_plugins_data(buffer, SIZE, "jpg", (void*)25, ready, NULL);
   emscripten_run_preload_plugins_data(buffer, SIZE, "jpg", (void*)33, ready, NULL); // twice to see different filenames
 
+  EM_ASM(reftestBlock());
   return 0;
 }
 

test/common.py

@@ -2209,7 +2209,21 @@ def make_reftest(self, expected):
     #   pngcrush -rem gAMA -rem cHRM -rem iCCP -rem sRGB infile outfile
     shutil.copy(expected, 'expected.png')
     create_file('reftest.js', '''
+      // We have some tests that don't perform rendering during `main` so
+      // the normal process of performing `doReftest` in `postRun` doesn't
+      // work.  These tests can delay the call to `doReftest` by calling
+      // `reftestBlock` and then calling `reftestUnblock` once they have
+      // done their rendering.
+      var reftestBlocked = false;
+      function reftestBlock() {
+        reftestBlocked = true;
+      }
+      function reftestUnblock() {
+        reftestBlocked = false;
+        doReftest();
+      }
       function doReftest() {
+        if (reftestBlocked) return;
         if (doReftest.done) return;
         doReftest.done = true;
         console.log('doReftest');
@@ -2330,9 +2344,10 @@ def reftest(self, filename, reference, reference_slack=0, *args, **kwargs):
     expected = [str(i) for i in range(0, reference_slack + 1)]
     self.make_reftest(reference)
     if self.proxied:
-      print("XXXX")
       assert 'post_build' not in kwargs
       kwargs['post_build'] = self.post_manual_reftest
+      create_file('fakereftest.js', 'var reftestUnblock = () => {}; var reftestBlock = () => {};')
+      kwargs['args'] += ['--pre-js', 'fakereftest.js']
     else:
       kwargs.setdefault('args', [])
       kwargs['args'] += ['--pre-js', 'reftest.js', '-sGL_TESTING']