wasm: enable MODULARIZE option and set EXPORT_NAME

Make Emscripten generate a global constructor function
("createQtAppInstance()") instead of a global javascript
module object.

This enables more fine-grained control over module
instantiation; previously the module object would be
created when the runtime javascript was evaluated, and
the number of emscripten module/instances was limited
to one per page.

Set EXPORT_NAME to “createQtAppInstance” which avoids
collisions with other non-Qt Emscripten modules on
the same page. A further improvement would be to include
the app name in EXPORT_NAME, but this is not done at
this time.

Update the code in qtloader.js to call the constructor
function instead of working on a global module object.
The qtloader.js API is functional before the wasm and
Emscripten modules have been instantiated; store properties
and forward to the Emscripten module when it's created.

Change-Id: I12c49a5b9a4a932bbc46fcc5e5ecc453fd0fe7f0
Reviewed-by: Lorn Potter <lorn.potter@gmail.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/cmake/QtWasmHelpers.cmake b/cmake/QtWasmHelpers.cmake
index bc5e455fcd..ecea701042 100644
--- a/cmake/QtWasmHelpers.cmake
+++ b/cmake/QtWasmHelpers.cmake
@@ -7,6 +7,16 @@ function (qt_internal_setup_wasm_target_properties wasmTarget)
     "SHELL:-s USE_WEBGL2=1"
     "--bind"
     "SHELL:-s FETCH=1")
+
+    # Enable MODULARIZE and set EXPORT_NAME, which makes it possible to
+    # create application instances using a global constructor function,
+    # e.g. let app_instance = await createQtAppInstance().
+    # (as opposed to MODULARIZE=0, where Emscripten creates a global app
+    # instance object at Javascript eval time)
+    target_link_options("${wasmTarget}" INTERFACE
+    "SHELL:-s MODULARIZE=1"
+    "SHELL:-s EXPORT_NAME=createQtAppInstance")
+
     target_compile_options("${wasmTarget}" INTERFACE --bind)
 
     # Hardcode wasm memory size. Emscripten does not currently support memory growth