Fix preserving layout(std140) directives with -sGL_EXPLICIT_UNIFORM_BINDING (#25839)

Fix preserving layout(std140) directives in WebGL shaders when using
`-sGL_EXPLICIT_UNIFORM_BINDING` WebGL extension. Improve the existing
test to catch the reported scenario.

Fixes #25828.

Author: juj

src/lib/libwebgl.js

@@ -3273,9 +3273,9 @@ for (/**@suppress{duplicate}*/var i = 0; i <= {{{ GL_POOL_TEMP_BUFFERS_SIZE }}};
     // Remove all the layout(binding = x) directives so that they do not make
     // their way to the actual WebGL shader compiler. These regexes get quite
     // hairy, check against https://regex101.com/ when working on these.
-    source = source.replace(/layout\s*\(.*?binding\s*=\s*([-\d]+).*?\)/g, ''); // "layout(binding = 3)" -> ""
+    source = source.replace(/layout\s*\(\s*binding\s*=\s*([-\d]+)\s*\)/g, ''); // "layout(binding = 3)" -> ""
     source = source.replace(/(layout\s*\((.*?)),\s*binding\s*=\s*([-\d]+)\)/g, '$1)'); // "layout(std140, binding = 1)" -> "layout(std140)"
-    source = source.replace(/layout\s*\(\s*binding\s*=\s*([-\d]+)\s*,(.*?)\)/g, 'layout($2)'); // "layout(binding = 1, std140)" -> "layout(std140)"
+    source = source.replace(/layout\s*\(\s*binding\s*=\s*([-\d]+)\s*,\s*(.*?)\)/g, 'layout($2)'); // "layout(binding = 1, std140)" -> "layout(std140)"
 
 #if GL_DEBUG
     dbg(`Shader source after removing layout binding directives: ${source}`;

test/browser/webgl2_ubo_layout_binding.c

@@ -83,6 +83,11 @@ int main(int argc, char *argv[])
     "out vec4 outColor;\n"
     "void main() { outColor = vec4(r, green.g, blue[0].b + blue[1].b, 1.0); }");
 
+  // The above shader compilation should preserve the std140 layout part in the uniforms, so
+  // make sure that did happen. (https://github.com/emscripten-core/emscripten/issues/25828)
+  assert(strstr(emscripten_webgl_get_shader_source_utf8(ps), "layout(std140) uniform Green"));
+  assert(strstr(emscripten_webgl_get_shader_source_utf8(ps), "layout(std140) uniform Blue"));
+
   GLuint program = CreateProgram(vs, ps);
   glUseProgram(program);