GL: implement EXT_texture_mirror_clamp_to_edge on ES and WebGL.

doc/opengl-support.dox

@@ -488,7 +488,7 @@ Extension                                   | Status
 @gl_extension{EXT,texture_compression_bptc} | done
 @gl_extension{EXT,texture_compression_s3tc_srgb} | done
 @gl_extension{EXT,clip_control}             | done
-@gl_extension{EXT,texture_mirror_clamp_to_edge} | |
+@gl_extension{EXT,texture_mirror_clamp_to_edge} | done
 @gl_extension{EXT,depth_clamp}              | done
 @gl_extension{IMG,texture_compression_pvrtc} | done
 @gl_extension2{KHR,texture_compression_astc_hdr,KHR_texture_compression_astc_hdr} | done
@@ -575,7 +575,7 @@ Extension                                   | Status
 @webgl_extension{EXT,polygon_offset_clamp}  | missing support in Emscripten
 @webgl_extension{EXT,clip_control}          | missing support in Emscripten
 @webgl_extension{EXT,depth_clamp}           | done
-@webgl_extension{EXT,texture_mirror_clamp_to_edge} | |
+@webgl_extension{EXT,texture_mirror_clamp_to_edge} | done
 @webgl_extension{KHR,parallel_shader_compile} | done
 @webgl_extension{NV,shader_noperspective_interpolation} | done (shading language only)
 @webgl_extension{OES,texture_float_linear}  | done

src/Magnum/GL/Sampler.cpp

@@ -173,9 +173,7 @@ Debug& operator<<(Debug& debug, const SamplerWrapping value) {
         #ifndef MAGNUM_TARGET_WEBGL
         _c(ClampToBorder)
         #endif
-        #ifndef MAGNUM_TARGET_GLES
         _c(MirrorClampToEdge)
-        #endif
         #undef _c
         /* LCOV_EXCL_STOP */
     }

src/Magnum/GL/Sampler.h

@@ -165,17 +165,18 @@ enum class SamplerWrapping: GLint {
     #endif
     #endif
 
-    #ifndef MAGNUM_TARGET_GLES
     /**
      * Mirror the texture once in negative coordinates and clamp to
      * edge after that. **Unavailable on rectangle textures.**
      * @requires_gl44 Extension @gl_extension{ARB,texture_mirror_clamp_to_edge},
      *      @gl_extension{ATI,texture_mirror_once} or @gl_extension{EXT,texture_mirror_clamp}
-     * @requires_gl Only separate @ref SamplerWrapping::MirroredRepeat or
+     * @requires_es_extension Extension @gl_extension{EXT,texture_mirror_clamp_to_edge}
-     *      @ref SamplerWrapping::ClampToEdge is available in OpenGL ES and
+     * @requires_webgl_extension Extension @webgl_extension{EXT,texture_mirror_clamp_to_edge}
-     *      WebGL.
      */
+    #ifndef MAGNUM_TARGET_GLES
     MirrorClampToEdge = GL_MIRROR_CLAMP_TO_EDGE
+    #else
+    MirrorClampToEdge = GL_MIRROR_CLAMP_TO_EDGE_EXT
     #endif
 };