Initial ARB_multi_bind usage in *Texture::bind().

doc/opengl-mapping.dox

@@ -62,8 +62,7 @@ OpenGL function                        | Matching API
 @fn_gl{BindRenderbuffer}               | not needed, handhled internally in @ref Renderbuffer
 @fn_gl{BindSampler}                    | |
 @fn_gl{BindSamplers}                   | |
-@fn_gl{BindTexture}, \n @fn_gl_extension{BindMultiTexture,EXT,direct_state_access} | @ref AbstractTexture::bind()
-@fn_gl{BindTextures}                   | |
+@fn_gl{BindTexture}, \n @fn_gl{BindTextures}, \n @fn_gl_extension{BindMultiTexture,EXT,direct_state_access} | @ref AbstractTexture::bind()
 @fn_gl{BindTransformFeedback}          | |
 @fn_gl{BindVertexArray}                | not needed, handhled internally in @ref Mesh
 @fn_gl{BindVertexBuffer}               | |

doc/opengl-support.dox

@@ -201,7 +201,7 @@ following:
 @extension{ARB,buffer_storage}               | |
 @extension{ARB,clear_texture}                | |
 @extension{ARB,enhanced_layouts}             | done (shading language only)
-@extension{ARB,multi_bind}                   | |
+@extension{ARB,multi_bind}                   | only single texture binding
 @extension{ARB,query_buffer_object}          | |
 @extension{ARB,texture_mirror_clamp_to_edge} | done
 @extension{ARB,texture_stencil8}             | done

src/Magnum/AbstractTexture.cpp

@@ -137,6 +137,10 @@ void AbstractTexture::bindImplementationDefault(GLint layer) {
 }
 
 #ifndef MAGNUM_TARGET_GLES
+void AbstractTexture::bindImplementationMulti(GLint layer) {
+    glBindTextures(layer, 1, &_id);
+}
+
 void AbstractTexture::bindImplementationDSA(GLint layer) {
     glBindMultiTextureEXT(GL_TEXTURE0 + layer, _target, (Context::current()->state().texture->bindings[layer] = _id));
 }
@@ -182,6 +186,10 @@ void AbstractTexture::mipmapImplementationDSA() {
 #endif
 
 void AbstractTexture::bindInternal() {
+    /* Using glBindTextures() here is meaningless, because the non-DSA
+       functions need to have the texture bound in *currently active* layer,
+       so we would need to call glActiveTexture() afterwards anyway. */
+
     Implementation::TextureState* const textureState = Context::current()->state().texture;
 
     /* If the texture is already bound in current layer, nothing to do */

src/Magnum/AbstractTexture.h

@@ -52,11 +52,15 @@ affect active bindings in user layers. %Texture limits and
 implementation-defined values (such as @ref maxColorSamples()) are cached, so
 repeated queries don't result in repeated @fn_gl{Get} calls.
 
-If extension @extension{EXT,direct_state_access} is available, @ref bind() uses
-DSA function to avoid unnecessary calls to @fn_gl{ActiveTexture}. Also all
-texture configuration and data updating functions use DSA functions to avoid
-unnecessary calls to @fn_gl{ActiveTexture} and @fn_gl{BindTexture}. See
-respective function documentation for more information.
+If extension @extension{ARB,multi_bind} is available, @ref bind() uses
+@fn_gl{BindTextures} to avoid unnecessary calls to @fn_gl{ActiveTexture}.
+Otherwise, if extension @extension{EXT,direct_state_access} is available,
+@ref bind() uses the DSA function.
+
+In addition, if extension @extension{EXT,direct_state_access} is available,
+also all texture configuration and data updating functions use DSA functions
+to avoid unnecessary calls to @fn_gl{ActiveTexture} and @fn_gl{BindTexture}.
+See respective function documentation for more information.
 
 If extension @extension{ARB,robustness} is available, image reading operations
 (such as @ref Texture::image()) are protected from buffer overflow. However, if
@@ -208,13 +212,14 @@ class MAGNUM_EXPORT AbstractTexture: public AbstractObject {
          * @brief Bind texture for rendering
          *
          * Sets current texture as active in given layer. Note that only one
-         * texture can be bound to given layer. If @extension{EXT,direct_state_access}
-         * is not available, the layer is made active before binding the
-         * texture.
+         * texture can be bound to given layer. If @extension{ARB,multi_bind}
+         * (part of OpenGL 4.4) or @extension{EXT,direct_state_access} is not
+         * available, the layer is made active before binding the texture.
          * @note This function is meant to be used only internally from
          *      @ref AbstractShaderProgram subclasses. See its documentation
          *      for more information.
-         * @see @ref maxLayers(), @fn_gl{ActiveTexture}, @fn_gl{BindTexture} or
+         * @see @ref maxLayers(), @fn_gl{ActiveTexture}, @fn_gl{BindTexture},
+         *      @fn_gl{BindTextures} or
          *      @fn_gl_extension{BindMultiTexture,EXT,direct_state_access}
          */
         void bind(Int layer);
@@ -248,6 +253,7 @@ class MAGNUM_EXPORT AbstractTexture: public AbstractObject {
     private:
         void MAGNUM_LOCAL bindImplementationDefault(GLint layer);
         #ifndef MAGNUM_TARGET_GLES
+        void MAGNUM_LOCAL bindImplementationMulti(GLint layer);
         void MAGNUM_LOCAL bindImplementationDSA(GLint layer);
         #endif
 

src/Magnum/Implementation/TextureState.cpp

@@ -41,12 +41,25 @@ TextureState::TextureState(Context& context, std::vector<std::string>& extension
     , maxColorSamples(0), maxDepthSamples(0), maxIntegerSamples(0), bufferOffsetAlignment(0)
     #endif
 {
+    /* Bind implementation */
+    #ifndef MAGNUM_TARGET_GLES
+    if(context.isExtensionSupported<Extensions::GL::ARB::multi_bind>()) {
+        extensions.push_back(Extensions::GL::ARB::multi_bind::string());
+        bindImplementation = &AbstractTexture::bindImplementationMulti;
+    } else if(context.isExtensionSupported<Extensions::GL::EXT::direct_state_access>()) {
+        /* Extension name added below */
+        bindImplementation = &AbstractTexture::bindImplementationDSA;
+    } else
+    #endif
+    {
+        bindImplementation = &AbstractTexture::bindImplementationDefault;
+    }
+
     /* DSA/non-DSA implementation */
     #ifndef MAGNUM_TARGET_GLES
     if(context.isExtensionSupported<Extensions::GL::EXT::direct_state_access>()) {
         extensions.push_back(Extensions::GL::EXT::direct_state_access::string());
 
-        bindImplementation = &AbstractTexture::bindImplementationDSA;
         parameteriImplementation = &AbstractTexture::parameterImplementationDSA;
         parameterfImplementation = &AbstractTexture::parameterImplementationDSA;
         parameterfvImplementation = &AbstractTexture::parameterImplementationDSA;
@@ -65,7 +78,6 @@ TextureState::TextureState(Context& context, std::vector<std::string>& extension
     } else
     #endif
     {
-        bindImplementation = &AbstractTexture::bindImplementationDefault;
         parameteriImplementation = &AbstractTexture::parameterImplementationDefault;
         parameterfImplementation = &AbstractTexture::parameterImplementationDefault;
         parameterfvImplementation = &AbstractTexture::parameterImplementationDefault;