qt - Combination QQuickFramebufferObject+texturing+GridView doesn't show items when you scroll to them -

what i'm doing, in short:

• deriving class myitem qquickframebufferobject. drawing simple textured triangle myitem. texture taken qml item.
• wrapping myitem in myitemwrapper.qml component. on component.oncompleted:, make delay , call myitem.update()
• i have scrollable (with mouse wheel) gridview of myitemwrapper items

the items in viewport show fine. when scroll down, items come viewport don't show @ all. show when hover them, since i've added test mousearea.onentered calls myitem.update(). i've observed 2 different systems different gpus.

i've tried enabling opengl debug logging testcase, prints no errors.

i've tried setting cachebuffer: number.max_safe_integer on gridview, no avail.

any ideas?

my code:

main.cpp:

#include <qqmlapplicationengine> #include <qguiapplication> #include "myitem.h"  int main(int argc, char** argv) {     qmlregistertype<myitem>("myitem", 1, 0, "myitem");      qguiapplication app(argc, argv);     qqmlapplicationengine engine;     engine.load(qurl(qstringliteral("qrc:/main.qml")));     return app.exec(); } 

myitem.cpp:

#include "myitem.h"  #include <qopenglframebufferobject> #include <qsgtextureprovider> #include <qsgtexture> #include <qquickwindow> #include <qopenglbuffer> #include <qopenglshaderprogram> #include "mesh.h"  class myitemrenderer : public qquickframebufferobject::renderer, protected qopenglfunctions { public:     myitemrenderer() {         initializeopenglfunctions();          m_program.addshaderfromsourcefile(qopenglshader::vertex, ":/flat.vert.glsl");         m_program.addshaderfromsourcefile(qopenglshader::fragment, ":/flat.frag.glsl");         m_program.bind();         m_program.bindattributelocation("apos", mesh::posattriblocation);         m_program.link();         m_program.setuniformvalue("utex", 0);     }      void synchronize(qquickframebufferobject* qqfbo){         auto item = (myitem*)qqfbo;          m_window = item->window();         m_tex = item->sourceitem()->textureprovider()->texture();     }      qopenglframebufferobject *createframebufferobject(const qsize &size) {         qopenglframebufferobjectformat format;         format.setattachment(qopenglframebufferobject::combineddepthstencil);         return new qopenglframebufferobject(size, format);     }      void render() {         gldisable(gl_depth_test);         glclearcolor(0.0, 0.0, 0.0, 0.0);         glclear(gl_color_buffer_bit);          m_program.bind();         m_mesh.vao.bind();          glactivetexture(gl_texture0);         m_tex->bind();         gldrawarrays(gl_triangles, 0, 3);          m_window->resetopenglstate();     }  private:     qquickwindow* m_window;     mesh m_mesh;     qsgtexture* m_tex;     qopenglshaderprogram m_program; };  qquickframebufferobject::renderer *myitem::createrenderer() const {     return new myitemrenderer(); } 

myitem.h:

#ifndef myitem_h #define myitem_h  #include <qquickframebufferobject> #include "propertyhelper.h" // file http://syncor.blogspot.bg/2014/11/qt-auto-property.html  class myitem : public qquickframebufferobject {     q_object      auto_property(qquickitem*, sourceitem)  public:     renderer *createrenderer() const; };  #endif 

mesh.h

#ifndef mesh_h #define mesh_h  #include <qopenglfunctions> #include <qopenglvertexarrayobject> #include <qopenglbuffer>  class mesh : protected qopenglfunctions {     template<class t>     int getnumbytes(std::vector<t> vec) {         return vec.size() * sizeof(t);     }  public:     mesh()         : vertexposbuffer(qopenglbuffer::vertexbuffer)     {         initializeopenglfunctions();          std::vector<float> vertexposdata {             0.0, 0.0,             1.0, 0.0,             1.0, 1.0         };          vao.create();         qopenglvertexarrayobject::binder binder(&vao);          vertexposbuffer.create();         vertexposbuffer.bind();         vertexposbuffer.setusagepattern(qopenglbuffer::staticdraw);         vertexposbuffer.allocate(vertexposdata.data(), getnumbytes(vertexposdata));          glenablevertexattribarray(posattriblocation);         vertexposbuffer.bind();         glvertexattribpointer(posattriblocation, 2, gl_float, false, 0, 0);     }      qopenglbuffer vertexposbuffer;     qopenglvertexarrayobject vao;      static const int posattriblocation = 1; };   #endif // mesh_h 

main.qml:

import qtquick 2.5 import qtquick.window 2.2  window {     visible: true     id: window     width: 700     height: 700     gridview {         id: grid         anchors.fill: parent         cellwidth: 350         cellheight: 350         model: 20         delegate: myitemwrapper { }     } } 

myitemwrapper.qml:

import qtquick 2.5 import myitem 1.0  item {     width: grid.cellwidth     height: grid.cellheight     rectangle {         id: texsource         x: -10000         layer.enabled: true          color: "red"         width: 100         height: 100     }      myitem {         anchors.fill: parent          id: myitem         sourceitem: texsource     }      mousearea {         id: mousearea         hoverenabled: true         anchors.fill: parent          onentered: {             myitem.update();         }     }      function connectsingleshot(sig, slot) {         var f = function() {             slot.apply(this, arguments)             sig.disconnect(f)         }         sig.connect(f)     }      component.oncompleted: {         connectsingleshot(window.afterrendering, function() {             myitem.update();         });     } } 

flat.frag.glsl:

#version 150  in highp vec2 vtexcoord; out vec4 outputcolor; uniform sampler2d utex;  void main() {     outputcolor = texture(utex, vtexcoord); } 

flat.vert.glsl:

#version 150  in highp vec2 apos; out highp vec2 vtexcoord;  void main() {     gl_position = vec4(apos, 0.0, 1.0);     vtexcoord = apos * .5  + .5; } 

i think problem related this older problem of mine. in mind, tried 2 things:

• reparent relevant items have parent null during myitem.update() line, reparent them back. intended avoid gl rendering being affected middleman component of gridview. result no items ever displayed, reason.
• use connections connect onvisiblechanged signal of myitemwrapper, , of parent, , of it's parent's parents. in signal handler had console.log. never got executed.

i've traced qt code down point:

http://code.qt.io/cgit/qt/qtdeclarative.git/tree/src/quick/items/qquickwindow.cpp?h=v5.9.1#n3148

here sets opacity=0 culled items. don't know how continue here though.