Added TransformFeedback::maxVertexStreams() limit query.

doc/opengl-mapping.dox

@@ -478,6 +478,7 @@ OpenGL function                         | Matching API
 @def_gl{MAX_VERTEX_ATTRIB_STRIDE}       | |
 @def_gl{MAX_VERTEX_ATTRIB_BINDINGS}     | |
 @def_gl{MAX_VERTEX_ATTRIB_RELATIVE_OFFSET} | |
+@def_gl{MAX_VERTEX_STREAMS}             | @ref TransformFeedback::maxVertexStreams()
 @def_gl{MAX_VIEWPORTS}                  | |
 @def_gl{MAX_VIEWPORT_DIMS}              | @ref AbstractFramebuffer::maxViewportSize()
 @def_gl{MIN_FRAGMENT_INTERPOLATION_OFFSET}, \n @def_gl{MAX_FRAGMENT_INTERPOLATION_OFFSET} | |

src/Magnum/Implementation/TransformFeedbackState.cpp

@@ -10,7 +10,7 @@ namespace Magnum { namespace Implementation {
 
 TransformFeedbackState::TransformFeedbackState(Context& context, std::vector<std::string>& extensions): maxInterleavedComponents{0}, maxSeparateAttributes{0}, maxSeparateComponents{0}
     #ifndef MAGNUM_TARGET_GLES
-    , maxBuffers{0}
+    , maxBuffers{0}, maxVertexStreams{0}
     #endif
 {
     #ifndef MAGNUM_TARGET_GLES

src/Magnum/Implementation/TransformFeedbackState.h

@@ -53,7 +53,8 @@ struct TransformFeedbackState {
         maxSeparateAttributes,
         maxSeparateComponents;
     #ifndef MAGNUM_TARGET_GLES
-    GLint maxBuffers;
+    GLint maxBuffers,
+        maxVertexStreams;
     #endif
 
     GLuint binding;

src/Magnum/Platform/magnum-info.cpp

@@ -612,6 +612,7 @@ MagnumInfo::MagnumInfo(const Arguments& arguments): Platform::WindowlessApplicat
         _h(ARB::transform_feedback3)
 
         _l(TransformFeedback::maxBuffers())
+        _l(TransformFeedback::maxVertexStreams())
     }
     #endif
 

src/Magnum/TransformFeedback.cpp

@@ -94,6 +94,18 @@ Int TransformFeedback::maxBuffers() {
 
     return value;
 }
+
+Int TransformFeedback::maxVertexStreams() {
+    if(!Context::current().isExtensionSupported<Extensions::GL::ARB::transform_feedback3>())
+        return 1;
+
+    GLint& value = Context::current().state().transformFeedback->maxVertexStreams;
+
+    if(value == 0)
+        glGetIntegerv(GL_MAX_VERTEX_STREAMS, &value);
+
+    return value;
+}
 #endif
 
 TransformFeedback::TransformFeedback(): _flags{ObjectFlag::DeleteOnDestruction} {

src/Magnum/TransformFeedback.h

@@ -147,6 +147,18 @@ class MAGNUM_EXPORT TransformFeedback: public AbstractObject {
          *      WebGL.
          */
         static Int maxBuffers();
+
+        /**
+         * @brief Max supported vertex stream count
+         *
+         * The result is cached, repeated queries don't result in repeated
+         * OpenGL calls. If extension @extension{ARB,transform_feedback3} (part
+         * of OpenGL 4.0) is not available, returns `1`.
+         * @see @fn_gl{Get} with @def_gl{MAX_VERTEX_STREAMS}
+         * @requires_gl Multiple vertex streams are not available in OpenGL ES
+         *      and WebGL.
+         */
+        static Int maxVertexStreams();
         #endif
 
         /**