Fix SDL_GL_ExtensionSupported (#22869)

It looks like this simply didn't work before.

Author: sbc100

src/library_sdl.js

@@ -3330,7 +3330,8 @@ var LibrarySDL = {
   // SDL 2
 
   SDL_GL_ExtensionSupported__proxy: 'sync',
-  SDL_GL_ExtensionSupported: (extension) => Module.ctx.getExtension(extension) | 0,
+  SDL_GL_ExtensionSupported__deps: ['$GLctx', '$UTF8ToString'],
+  SDL_GL_ExtensionSupported: (extension) => GLctx?.getExtension(UTF8ToString(extension)) ? 1 : 0,
 
   SDL_DestroyWindow: (window) => {},
 

test/browser/test_sdl_gl_extensions.c

@@ -0,0 +1,32 @@
+#include "SDL/SDL.h"
+#include "SDL/SDL_opengl.h"
+
+#include <stdio.h>
+#include <string.h>
+#include <assert.h>
+
+int main(int argc, char *argv[]) {
+  SDL_Surface *screen;
+
+  assert(SDL_Init(SDL_INIT_VIDEO) == 0);
+  SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
+  screen = SDL_SetVideoMode( 640, 480, 16, SDL_OPENGL);
+  assert(screen);
+
+  char *extensions = (char*)glGetString(GL_EXTENSIONS);
+  printf("extensions: %s\n", extensions);
+  assert(extensions);
+
+  int supported = SDL_GL_ExtensionSupported("foobar");
+  assert(!supported);
+
+  char* end = strchr(extensions, ' ');
+  *end = '\0';
+  printf("testing for extension: %s\n", extensions);
+  supported = SDL_GL_ExtensionSupported(extensions);
+  printf("supported: %d\n", supported);
+  assert(supported);
+
+  SDL_Quit();
+  return 0;
+}

test/test_browser.py

@@ -1479,6 +1479,10 @@ def test_sdl_canvas_size(self):
                     args=['-O2', '--minify=0', '--shell-file',
                           test_file('browser/test_sdl_canvas_size.html'), '-lSDL', '-lGL'])
 
+  @requires_graphics_hardware
+  def test_sdl_gl_extensions(self):
+    self.btest_exit('test_sdl_gl_extensions.c', args=['-lSDL', '-lGL'])
+
   @requires_graphics_hardware
   def test_sdl_gl_read(self):
     # SDL, OpenGL, readPixels