Support for ARB_texture_mirror_clamp_to_edge.

This functionality was present in ATI_texture_mirror_once and
EXT_texture_mirror_clamp for ages, now (strict subset of) it is in core
OpenGL 4.4 too.

src/Context.cpp

@@ -82,7 +82,9 @@ const std::vector<Extension>& Extension::extensions(Version version) {
         _extension(GL,AMD,vertex_shader_layer),             // done
         _extension(GL,AMD,shader_trinary_minmax),           // done
         _extension(GL,ARB,robustness),                      // done
+        _extension(GL,ATI,texture_mirror_once),
         _extension(GL,EXT,texture_filter_anisotropic),      // done
+        _extension(GL,EXT,texture_mirror_clamp),
         _extension(GL,EXT,direct_state_access),
         _extension(GL,GREMEDY,string_marker)};              // done
     static const std::vector<Extension> extensions300{

src/Extensions.h

@@ -161,10 +161,13 @@ namespace GL {
         _extension(GL,ARB,texture_mirror_clamp_to_edge, GL210, GL440) // #149
         _extension(GL,ARB,texture_stencil8,             GL210, GL440) // #150
         _extension(GL,ARB,vertex_type_10f_11f_11f_rev,  GL300, GL440) // #151
+    } namespace ATI {
+        _extension(GL,ATI,texture_mirror_once,          GL210,  None) // #221
     } namespace EXT {
         _extension(GL,EXT,texture_filter_anisotropic,   GL210,  None) // #187
         /* EXT_framebuffer_object, EXT_packed_depth_stencil, EXT_framebuffer_blit,
            EXT_framebuffer_multisample replaced with ARB_framebuffer_object */
+        _extension(GL,EXT,texture_mirror_clamp,         GL210,  None) // #298
         _extension(GL,EXT,gpu_shader4,                  GL210, GL300) // #326
         _extension(GL,EXT,packed_float,                 GL210, GL300) // #328
         _extension(GL,EXT,texture_array,                GL210, GL300) // #329

src/Sampler.h

@@ -113,11 +113,24 @@ class Sampler {
              * @requires_es_extension %Extension @es_extension{NV,texture_border_clamp}
              */
             #ifndef MAGNUM_TARGET_GLES
-            ClampToBorder = GL_CLAMP_TO_BORDER
+            ClampToBorder = GL_CLAMP_TO_BORDER,
             #else
-            ClampToBorder = GL_CLAMP_TO_BORDER_NV
+            ClampToBorder = GL_CLAMP_TO_BORDER_NV,
             #endif
             #endif
+
+            #ifndef MAGNUM_TARGET_GLES
+            /**
+             * Mirror the texture once in negative coordinates and clamp to
+             * edge after that.
+             * @requires_gl44 %Extension @extension{ARB,texture_mirror_clamp_to_edge},
+             *      @extension{ATI,texture_mirror_once} or @extension{EXT,texture_mirror_clamp}
+             * @requires_gl Only separate @ref Magnum::Sampler::Wrapping "Wrapping::MirroredRepeat"
+             *      or @ref Magnum::Sampler::Wrapping "Wrapping::ClampToEdge"
+             *      is available in OpenGL ES.
+             */
+            MirrorClampToEdge = GL_MIRROR_CLAMP_TO_EDGE
+            #endif
         };
 
         #ifndef MAGNUM_TARGET_GLES3