On 14 April 2017 at 00:25, Ch'Gans <chg...@gna.org> wrote: > On 13 April 2017 at 18:52, Sean Harmer <sean.har...@kdab.com> wrote: >> Hi, >> >> On 13/04/2017 06:15, Ch'Gans wrote: >>> >>> On 13 April 2017 at 14:38, Ch'Gans <chg...@gna.org> wrote: >>>> >>>> Hi, >>>> >>>> I would like to be able to select at run-time how my entities are >>>> rendered (ideally on a per entity basis). >>>> I would like to have 3 choices: >>>> - 1. wireframe >>>> - 2. shaded >>>> - 3. shaded + wireframe >>>> >>>> I had a look at the wire frame QML example, and translated it to C++. >>>> The code is working. I have simplified the fragment shader, as i don't >>>> need fancy light effect, other than a shaded color per face. >>>> These shaders allow me to achieve 2 & 3. But my feeling is that i need >>>> something completely different to render a 'transparent' wireframe >>>> only. >> >> >> You can do it a number of ways: >> >> 1) One approach is indeed to use polygon mode but as you've noticed this >> renderstate is missing from Qt 3D but should be easy to add. >> >> 2) You could adjust the shader from 3 such that when in the fragment shader >> you decide if a fragment is part of the line or part of the shaded mesh, >> instead of shading it, you simply call discard() to throw that fragment >> away. > > Bummer! The only thing I was missing is the discard() call... See, I'm > a real noob! ;) > This, with the NoCulling simply works for 1, 2 &3! > > >> >> 3) Use custom geometry to render your wireframe however you see fit. This >> may be as simple as using a different index attribute/buffer with your >> existing vertex data buffer(s), or you may want to create entirely new >> geometry if you want something other than lines joining the original >> vertices. For, example if you want an extruded lattice type effect for your >> wire frame. You may even be able to get away with simply using lines as the >> primitive type instead of triangles. Depends upon your geometry. >> >> 4) Render the same geometry but with an alpha blended material. > > I tried that one, with no luck as i certainly missed something. I've > read somewhere that you had to manage the z ordering in case you have > several transparent objects, so i gave up. > >> >> 5) Probably a bunch of other ways I can't think of without another cup of >> tea... >> >>>> Reading through OpenGL materials, it looks like i need things like >>>> glPolygonMode, reading through Qt3D leads me to >>>> QGeometryRenderer::PrimitiveType. >>>> >>>> But i am having problems connecting the dots. >>>> PrimitiveType is a property of QGeometryRenderer, which means that it >>>> is closely related with my buffer data and how the data are arranged >>>> within the buffer. >>>> So If i want to switch from 'shaded' to wireframe I need to change my >>>> data (and my shader code too), surely there is to be a way to use the >>>> same data buffer to achieve the 3 rendering modes. Should I use a 2 >>>> passes rendering? The first one renders (or not) the face shades and >>>> the second one renders (or not) the wireframes? Actually this should >>>> even be a 3 passes: back of wireframe (or not), shaded faces (or not) >>>> and front of wireframe (or not)... >> >> >> No need to render something twice to see its back and front sides. Use a >> QCullFace render state with the mode set to NoCulling. By default, it's set >> to cull the back faces because most often meshes are closed so there's no >> point in rasterizing the back faces as they will never be seen. > > Yes, i get the picture now. I was thinking this way because i forgot > about the 'discard' feature. > >> >>>> Is this the right approach? Or should I instead define 3 materials and >>>> simply switch the material as i want a different drawing style? >>>> >>>> Last thing is that my input data are triangulated polygon with holes, >>>> but i have as well access to the original polygon with holes alone. >>>> And i actually don't want to render the internal (triangulation) edges >>>> of my polygonal faces (up and down) or rectangular faces (side ones). >>>> So basically in shaded mode, i only need to calculate the color per >>>> geometric face (as oppose to triangular face) ... >> >> >> To exclude some of the triangle edges you need an additional per vertex >> attribute to use as a flag. Have a read through >> >> http://strattonbrazil.blogspot.co.uk/2011/09/single-pass-wireframe-rendering_11.html > > Thanks for sharing, this article also explain the what, why and how of > the shader code from the wireframe example. > > If i wanted to make a generic material (one you can use on any mesh, > eg QCylinderGeometry or QMesh), then i wouldn't use this. But if i use > exclusively my custom geometry this is the way to go. > >> >> for the details. >> >>>> >>>> PS: I've spent serious time yesterday reading through >>>> https://learnopengl.com, although I think i now understand (way >>>> better) how OpenGL works and how to use it, Qt3D seems to be way more >>>> than a convenience wrapper around the OpenGL API. >>>> I couldn't find a place in Qt3D where you would manipulate OpenGL >>>> directly (eg calling glFooBar()). I am not even sure if it was design >>>> too do this sort of things. >>> >>> >>> Answering myself partially: >>> QRenderState provides lot of these. Eg.: glCullFace() => QCullFace, >>> glFrontFace() => QFrontFace, ... >>> >>> Bu as far as i can understand OpenGL and Qt3D, i would say that Qt3D >>> simply doesn't support the OpenGL polygon mode. Maybe because it's >>> either sort-of deprecated, or there are other (better?) ways to do >>> this sort of things... >> >> >> Nope, it just slipped under the radar and you're the first person to ask for >> it. Should be simple to add. Take a look at the other render states if you >> want to contribute it. > > I had a look at the source code, I might give it a try over the week-end. > > Looks like that I "just" need to: > - add a new state derived from GenericState (with 2 glEnum params) > - implement the apply() > - add an enum value to Render::StateMask, > - add code to RenderStateSet::resetMasked() > - add stuff to StateVariant > - implement the public QPolygonMode and all the glue that go with it > (private, data, ...). > - 2 enums to map with glEnum face and mode in the public API > > Am I missing any important steps?
Oh yes! The QOpenGLFunctions class doesn't provide glPoygonMode() ... Too bad! :( Chris > > >> >> Cheers, >> >> Sean >> >> -- >> Dr Sean Harmer | sean.har...@kdab.com | Managing Director UK >> KDAB (UK) Ltd, a KDAB Group company >> Tel. +44 (0)1625 809908; Sweden (HQ) +46-563-540090 >> Mobile: +44 (0)7545 140604 >> KDAB - Qt Experts >> _______________________________________________ >> Interest mailing list >> Interest@qt-project.org >> http://lists.qt-project.org/mailman/listinfo/interest _______________________________________________ Interest mailing list Interest@qt-project.org http://lists.qt-project.org/mailman/listinfo/interest
