[Feature] texturing support for vector layer

[NEDJIMAbelgacem]

Added texturing support for QGIS 3D

• Now from the symbol properties you can select an image to be displayed on the surfaces of buildings as diffuse map.
• The user can also change the scale of textures from the symbol properties as you can see in these screenshots:

• Some visual issue may appear when using textures. these issues relates to the normals of surfaces that you may be able to fix by checking "add back faces" and playing around with the invert normals and culling mode in the symbol properties.
• I modified a bit of the QgsTessellatedPolygonGeometry constructor so that every Qt3DRender::QAttribute of the geometry will be constructed properly because setting them after constructing the object can be confusing and we don't want it to construct objects that we won't need later on. I also provided default parameters for the constructor so we don't have problems with existing code.

[m-kuhn]

Nice start!

Welcome Belgacem.

[nyalldawson]

Looking at https://stackoverflow.com/questions/50944249/create-qtextureimage-from-qimage , it seems there's a means to directly construct textures from a QImage object. If this is the case, then you could use QgsImageCache::pathAsImage() (via QgsApplication::imageCache()->pathAsImage(...)) here instead of directly loading from a local file.

There's two benefits to this approach

1. If the image has been previously loaded then it'll save a bunch of work
2. QgsImageCache supports base64 encoded image paths. This allows for embedding images directly inside a QgsProject, so that the project becomes portable and there's no path issues when you share the project (or QML style) with others. To enable this you'd also need to chance the textureFile widget in the ui file to a QgsImageSourceLineEdit widget (which adds the UI for users to embed pictures).

[NEDJIMAbelgacem]

I didn't know about that. I will change the textureFile widget to QgsImageSourceLineEdit and use QgsImageCache and make another commit.
Thanks for the suggestion!

[nyalldawson]

Wow, you've really "hit the ground running"!! Great start to GSOC @NEDJIMAbelgacem !

[ismailsunni]

Awesome @NEDJIMAbelgacem
You can also add some gifs to show the 3D or how the setting works (nice to have/see but not mandatory for sure)

[timlinux]

Looking awesome @NEDJIMAbelgacem !

[wonder-sk]

It's looking great - nice work!

I have left a couple of suggestions below on how to further improve the code...

[NEDJIMAbelgacem]

Hi,
The separation between roofs and walls in now complete although it's not very good now due to technical limitations of how we classify a vector layer feature's geometry as part of wall or roof.
I made a new combo box that selects which facade we want to render (wall, roofs or walls and roofs). To know if a triangle is a wall or a roof I calculate the degrees between the triangle's normal and the horizontal plane, if the angle is less than 10 degrees the triangle is a part of a roof, otherwise it's part of a wall.
To take advantage of the walls and roofs separation, the user needs to create 2 rules in the rule based rendering each one having it's own symbol.
The user can also change the scale and rotation of textures.
I noticed that the Phong material gets reused in parts where there is no need to use textures. I hide the texture UI widgets every time except when it is needed for the vector layer.

[wonder-sk]

Very nice! We will probably still need to do some further work on texturing, but this one is good to go...