c++ - glDrawElementsInstancedBaseInstance() requires preceding glVertexArrayVertexBuffer() -

my objective draw textured quads screen rendering text. trying use gldrawelementsinstancedbaseinstance render each glyph quad instance of same mesh. in order convey individual information each character quad (like position, size , glyph index) use 2 buffers (quadstorage, charstorage), sources vertex attributes (vec2 quadpos,vec2 quadsize, unsigned int glyphindex) advance each instance.

because may want change text on screen occasionally, need way stream buffers. in application, have used immutable buffers (initialized glbufferstorage) mapped gl_map_persistent_bit , gl_map_coherent_bit flags set, enables me map entire buffer "forever" , use mapped pointer c-array. avoid writing memory being read create storage 3 times large need , can use new range in buffer each stream upload. when want use updated data in shaders have rebind buffer bindings reference updated range in buffer using glbindbufferrange gl_uniform_buffers , glvertexarrayvertexbuffer gl_array_buffers bound vao.

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but recently, ran few problems. i have found gldrawelementsinstancedbaseinstance throws invalid_operation error if not call glvertexarrayvertexbuffer each frame. wanted stream attribute buffers once when loading screen , let frame loop go on, unless kept updatecharstorage() function call (which writes pending data mapped pointer , updates buffer binding offset glvertexarrayvertexbuffer) in frame loop, throw error.

at beginning of research have read gldrawelementsinstancedbaseinstance may throw invalid_operation if buffer object name bound enabled array , buffer object's data store mapped, confused me more, because had buffer mapped beginning , worked. me seems calls glvertexarrayvertexbuffer causing problems, not find fix. have assured myself call glvertexarrayvertexbuffer right after data upload , parameters correct. else causing error/behaviour?

this procedure use create buffer storage can stream to:

unsigned int storage; glcreatebuffers(1, &storage); glnamedbufferstorage(storage, capacity, dataptr, gl_map_write_bit| gl_map_persistent_bit| gl_map_coherent_bit); void* mapped_ptr = glmapnamedbufferrange(storage, 0, capacity, gl_map_write_bit| gl_map_persistent_bit| gl_map_coherent_bit); 

if want use buffer vertex attributes in shader do:

glvertexarrayvertexbuffer(vao, buffer_binding, storage, 0/*offset*/, stride); glenablevertexarrayattrib(vao, attribute_index); glvertexarrayattribbinding(vao, attribute_index, buffer_binding); glvertexarrayattribformat(vao, attribute_index, count, type, normalize, offset); 

streaming works (this updatecharstorage() does):

//...align update offset opengls alignment requirements... std::memcpy(mapped_ptr + update_offset, data_ptr, upload_size); glvertexarrayvertexbuffer(vao, buffer_binding, storage, update_offset, stride); 

when remove glvertexarrayvertexbuffer call frame loop error, though vao binding has been initialized (with glvertexarrayvertexbuffer) , draw calls should know buffer use.