GL: drop std::pair from texture state tracker internals.

Apparently even `= {}` was broken for std::pair once, not to mention the
unnecessary extra overhead with this type not being trivially copyable.
Good riddance.

src/Magnum/GL/AbstractTexture.cpp

@@ -119,13 +119,11 @@ void AbstractTexture::unbind(const Int textureUnit) {
     Implementation::TextureState& textureState = Context::current().state().texture;
 
     /* If given texture unit is already unbound, nothing to do */
-    if(textureState.bindings[textureUnit].second == 0) return;
+    if(textureState.bindings[textureUnit].second() == 0) return;
 
     /* Unbind the texture, reset state tracker */
     Context::current().state().texture.unbindImplementation(textureUnit);
-    /* libstdc++ since GCC 6.3 can't handle just = {} (ambiguous overload of
+    textureState.bindings[textureUnit] = {};
-       operator=) */
-    textureState.bindings[textureUnit] = std::pair<GLenum, GLuint>{};
 }
 
 void AbstractTexture::unbindImplementationDefault(const GLint textureUnit) {
@@ -135,8 +133,8 @@ void AbstractTexture::unbindImplementationDefault(const GLint textureUnit) {
     if(textureState.currentTextureUnit != textureUnit)
         glActiveTexture(GL_TEXTURE0 + (textureState.currentTextureUnit = textureUnit));
 
-    CORRADE_INTERNAL_ASSERT(textureState.bindings[textureUnit].first != 0);
+    CORRADE_INTERNAL_ASSERT(textureState.bindings[textureUnit].first() != 0);
-    glBindTexture(textureState.bindings[textureUnit].first, 0);
+    glBindTexture(textureState.bindings[textureUnit].first(), 0);
 }
 
 #ifndef MAGNUM_TARGET_GLES
@@ -146,7 +144,7 @@ void AbstractTexture::unbindImplementationMulti(const GLint textureUnit) {
 }
 
 void AbstractTexture::unbindImplementationDSA(const GLint textureUnit) {
-    CORRADE_INTERNAL_ASSERT(Context::current().state().texture.bindings[textureUnit].first != 0);
+    CORRADE_INTERNAL_ASSERT(Context::current().state().texture.bindings[textureUnit].first() != 0);
     glBindTextureUnit(textureUnit, 0);
 }
 #endif
@@ -184,9 +182,9 @@ void AbstractTexture::bindImplementationMulti(const GLint firstTextureUnit, Cont
             ids[i] = id;
         }
 
-        if(textureState.bindings[firstTextureUnit + i].second != id) {
+        if(textureState.bindings[firstTextureUnit + i].second() != id) {
             different = true;
-            textureState.bindings[firstTextureUnit + i].second = id;
+            textureState.bindings[firstTextureUnit + i].second() = id;
         }
     }
 
@@ -235,9 +233,7 @@ AbstractTexture::~AbstractTexture() {
     /* Remove all bindings */
     for(auto& binding: Context::current().state().texture.bindings) {
         /* MSVC 2015 needs the parentheses around */
-        /* libstdc++ since GCC 6.3 can't handle just = {} (ambiguous overload
+        if(binding.second() == _id) binding = {};
-           of operator=) */
-        if(binding.second == _id) binding = std::pair<GLenum, GLuint>{};
     }
 
     #if !defined(MAGNUM_TARGET_GLES2) && !defined(MAGNUM_TARGET_WEBGL)
@@ -335,7 +331,7 @@ void AbstractTexture::bind(Int textureUnit) {
     Implementation::TextureState& textureState = Context::current().state().texture;
 
     /* If already bound in given texture unit, nothing to do */
-    if(textureState.bindings[textureUnit].second == _id) return;
+    if(textureState.bindings[textureUnit].second() == _id) return;
 
     /* Update state tracker, bind the texture to the unit */
     textureState.bindings[textureUnit] = {_target, _id};
@@ -525,7 +521,7 @@ void AbstractTexture::bindInternal() {
     Implementation::TextureState& textureState = Context::current().state().texture;
 
     /* If the texture is already bound in current unit, nothing to do */
-    if(textureState.bindings[textureState.currentTextureUnit].second == _id)
+    if(textureState.bindings[textureState.currentTextureUnit].second() == _id)
         return;
 
     /* Set internal unit as active if not already, update state tracker */
@@ -535,7 +531,7 @@ void AbstractTexture::bindInternal() {
         glActiveTexture(GL_TEXTURE0 + (textureState.currentTextureUnit = internalTextureUnit));
 
     /* If already bound in given texture unit, nothing to do */
-    if(textureState.bindings[internalTextureUnit].second == _id) return;
+    if(textureState.bindings[internalTextureUnit].second() == _id) return;
 
     /* Update state tracker, bind the texture to the unit. Not directly calling
        glBindTexture() here because we may need to include various

src/Magnum/GL/Buffer.cpp

@@ -603,9 +603,7 @@ void Buffer::textureWorkaroundAppleBefore() {
 
         /* Unbind the texture, reset state tracker */
         glBindTexture(GL_TEXTURE_BUFFER, 0);
-        /* libstdc++ since GCC 6.3 can't handle just = {} (ambiguous overload
+        textureState.bindings[textureUnit] = {};
-           of operator=) */
-        textureState.bindings[textureUnit] = std::pair<GLenum, GLuint>{};
         textureState.bufferTextureBound.set(textureUnit, false);
     }
 }

src/Magnum/GL/Implementation/State.cpp

@@ -26,6 +26,7 @@
 #include "State.h"
 
 #include <Corrade/Containers/ArrayTuple.h>
+#include <Corrade/Containers/Pair.h>
 #include <Corrade/Utility/Assert.h>
 
 #include "Magnum/GL/Context.h"
@@ -83,7 +84,7 @@ std::pair<Containers::ArrayTuple, State&> State::allocate(Context& context, std:
     Containers::ArrayView<ShaderState> shaderStateView;
     Containers::ArrayView<ShaderProgramState> shaderProgramStateView;
     Containers::ArrayView<TextureState> textureStateView;
-    Containers::ArrayView<std::pair<GLenum, GLuint>> textureBindings;
+    Containers::ArrayView<Containers::Pair<GLenum, GLuint>> textureBindings;
     #if !defined(MAGNUM_TARGET_GLES2) && !defined(MAGNUM_TARGET_WEBGL)
     Containers::ArrayView<TextureState::ImageBinding> imageBindings;
     #endif

src/Magnum/GL/Implementation/TextureState.cpp

@@ -43,7 +43,7 @@ namespace Magnum { namespace GL { namespace Implementation {
 using namespace Containers::Literals;
 
 TextureState::TextureState(Context& context,
-    Containers::ArrayView<std::pair<GLenum, GLuint>> bindings,
+    Containers::ArrayView<Containers::Pair<GLenum, GLuint>> bindings,
     #if !defined(MAGNUM_TARGET_GLES2) && !defined(MAGNUM_TARGET_WEBGL)
     Containers::ArrayView<ImageBinding> imageBindings,
     #endif
@@ -547,7 +547,7 @@ TextureState::TextureState(Context& context,
 }
 
 void TextureState::reset() {
-    for(std::pair<GLenum, GLuint>& i: bindings)
+    for(Containers::Pair<GLenum, GLuint>& i: bindings)
         i = {{}, State::DisengagedBinding};
     #if !defined(MAGNUM_TARGET_GLES2) && !defined(MAGNUM_TARGET_WEBGL)
     for(ImageBinding& i: imageBindings)

src/Magnum/GL/Implementation/TextureState.h

@@ -25,7 +25,7 @@
     DEALINGS IN THE SOFTWARE.
 */
 
-#include <utility> /* std::pair */
+#include <Corrade/Containers/Pair.h>
 #include <Corrade/Containers/ArrayView.h>
 
 #include "Magnum/Magnum.h"
@@ -74,7 +74,7 @@ struct TextureState {
     #endif
 
     explicit TextureState(Context& context,
-        Containers::ArrayView<std::pair<GLenum, GLuint>> bindings,
+        Containers::ArrayView<Containers::Pair<GLenum, GLuint>> bindings,
         #if !defined(MAGNUM_TARGET_GLES2) && !defined(MAGNUM_TARGET_WEBGL)
         Containers::ArrayView<ImageBinding> imageBindings,
         #endif
@@ -187,7 +187,7 @@ struct TextureState {
     /* Texture type, texture object ID. While not true, for simplicity this
        assumes that each slot can have just one ID bound, not one ID per
        texture type. */
-    Containers::ArrayView<std::pair<GLenum, GLuint>> bindings;
+    Containers::ArrayView<Containers::Pair<GLenum, GLuint>> bindings;
     #if defined(CORRADE_TARGET_APPLE) && !defined(MAGNUM_TARGET_GLES)
     Math::BitVector<80> bufferTextureBound;
     #endif