Why doesn't WebGL2 queryCounterEXT link?

[Joyoslive]

Hi,
I've been trying to profile a webgl2 renderer that compiles with emscripten. I found the header file containing all the necessary defines as well as a prototype function for emscripten_webgl2_queryCounterEXT. However, when I try to use this function I get an "undefined symbol" error. If anyone has any idea as to what I need to do to make this link correctly I would be very grateful.

[sbc100]

I believe the indended user-facing symbol is glQueryCounterEXT . This seems to be defined in library_webgl.js:

emscripten/src/library_webgl.js

Lines 1848 to 1854 in 574f4f4

	glQueryCounterEXT__sig: 'vii',
	glQueryCounterEXT: function(id, target) {
	#if GL_ASSERTIONS
	GL.validateGLObjectID(GL.queries, id, 'glQueryCounterEXT', 'id');
	#endif
	GLctx.disjointTimerQueryExt['queryCounterEXT'](GL.queries[id], target);
	},

Does that symbol not work for you?

[Joyoslive]

glQueryCounterEXT does not seem to exist in C++. Where would this be declared? I might have missed including some header.

[sbc100]

I see a declaration in GLES2/gl2ext.h and in webgl/webgl1_ext.h.. are they don't working for some reason?:

$ git grep glQueryCounterEXT system/include/
system/include/GLES2/gl2ext.h:GL_APICALL void GL_APIENTRY glQueryCounterEXT (GLuint id, GLenum target);
system/include/webgl/webgl1_ext.h:WEBGL_APICALL void GL_APIENTRY emscripten_glQueryCounterEXT(GLuint id, GLenum target);
system/include/webgl/webgl1_ext.h:WEBGL_APICALL void GL_APIENTRY glQueryCounterEXT(GLuint id, GLenum target);

[sbc100]

It looks like emscripten_webgl2_queryCounterEXT was added to system/lib/gl/webgl2_ext.h back in #6254 but I don't see anywhere where that symbol is defined, even back in that change. @juj, was this a mistake? It doesn't seem the follow the naming convention of any other symbols.

[juj]

I believe the indended user-facing symbol is glQueryCounterEXT

This is correct.

timer queries in WebGL are little bit awkward, because there are two separate extension versions depending on which core WebGL context version one initializes. In Emscripten we actually paper over this behavior, and fuse the functions into one.

It looks like emscripten_webgl2_queryCounterEXT was added to system/lib/gl/webgl2_ext.h back in #6254 but I don't see anywhere where that symbol is defined, even back in that change. @juj, was this a mistake?

This indeed is a mistake.

It doesn't seem the follow the naming convention of any other symbols.

The naming convention here is a bit complex, and deserves a mention.

For all WebGL extensions that define new functions, the function naming of the functions overlays on top of the existing GLES2/GLES3 function names for portability.

So for example, ANGLE_instanced_arrays extension provides three functions

    undefined drawArraysInstancedANGLE(GLenum mode, GLint first, GLsizei count, GLsizei primcount);
    undefined drawElementsInstancedANGLE(GLenum mode, GLsizei count, GLenum type, GLintptr offset, GLsizei primcount);
    undefined vertexAttribDivisorANGLE(GLuint index, GLuint divisor); 

In the native GLES2/GLES3 world, the same types of extensions existed, with native gl* function API names. So these functions became

WEBGL_APICALL void GL_APIENTRY emscripten_glDrawArraysInstancedANGLE(GLenum mode, GLint first, GLsizei count, GLsizei primcount);
WEBGL_APICALL void GL_APIENTRY emscripten_glDrawElementsInstancedANGLE(GLenum mode, GLsizei count, GLenum type, GLintptr offset, GLsizei primcount);
WEBGL_APICALL void GL_APIENTRY emscripten_glVertexAttribDivisorANGLE(GLuint index, GLuint divisor);
WEBGL_APICALL void GL_APIENTRY glDrawArraysInstancedANGLE(GLenum mode, GLint first, GLsizei count, GLsizei primcount);
WEBGL_APICALL void GL_APIENTRY glDrawElementsInstancedANGLE(GLenum mode, GLsizei count, GLenum type, GLintptr offset, GLsizei primcount);
WEBGL_APICALL void GL_APIENTRY glVertexAttribDivisorANGLE(GLuint index, GLuint divisor);

(The emscripten_ aliases being there for the glGetProcAddress() and offscreen framebuffer features)

However, there are then some extensions that are unique to WebGL that there does not exist a corresponding native GLES2/GLES3 extension.

Currently such extensions are:

• WEBGL_lose_context
• WEBGL_debug_shaders
• WEBGL_compressed_texture_astc

These come with new WebGL functions that don't exist in native GL/GLES. For example:

[Exposed=(Window,Worker), LegacyNoInterfaceObject]
interface WEBGL_lose_context {
      undefined loseContext();
      undefined restoreContext();
};

I did not want to step in to the existing native GL/GLES gl* namespace and invent new native GL sounding function names, such as

glLoseContext();
glRestoreContext();

since that would kind of confuse with the existing native specifications and make it read like it was an official core GL/GLES thing.

So for these functions, I opted to go for the naming scheme

emscripten_webgl_....()
emscripten_webgl2_....()

for WebGL 1 and WebGL 2 extensions and these extensions will be available by a #include <webgl/webgl1_ext.h> and #include <webgl/webgl2_ext.h> respectively.

The EXT_disjoint_timer_query_webgl2 extension brings a new function, so that is probably why I had written a declaration of a function emscripten_webgl2_queryCounterEXT in webgl2_ext.h.

However, the implementation of that function was actually merged into the general glQueryCounterEXT function, so no new functions were actually created. Posted PR #19158 to clean up this function name.