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? > > 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
