[Interest] Drawing dashed line with QSGSimpleMaterialShader

[Artem Fedoskin]

Hi Gunnar,

Thank you for your reply.

> An alternative approach would be to generate the line segments for the
dashes and combining that with
QSGGeometry::>defaultAttributes_ColorizedPoint2D() and
QSGVertexColorMaterial. It will be a bit more work to prepare and take up a
bit more >memory, but on the plus side, it will batch in the renderer, so
it will probably be faster to draw if you have many instances of these
>dashed objects. The modelview/cos based implementation you link to will
not support batching because each line needs a unique >shader state, the
model view matrix and perhaps also the source point.

Initially I wanted to choose this approach but then I thought that with
custom shaders it makes more sense as I can separate geometry and material.
I didn't know that batching is not applicable to shaders. Are there any
ways to do it with shaders and allow batching?

Another question - is there any way to draw text solely in Scene Graph
using QSG classes? I need to draw a lot of text labels and what only came
to my mind is to draw them using QPainter on a QImage and store it as a
QSGSimpleTextureNode in the node itself.

Regards, Artem

2016-06-06 7:39 GMT+02:00 Gunnar Sletta <gunnar at sletta.org>:

>
> > On 05 Jun 2016, at 00:50, Artem Fedoskin <afedoskin3 at gmail.com> wrote:
> >
> > As I understand there is no way to draw dashed line in Qt Quick Scene
> Graph so I decided to create shader material to do this.
> > I'm trying to apply this approach
> http://korkd.com/2012/02/15/dashed-lines/ to this example
> http://doc.qt.io/qt-5/qtquick-scenegraph-simplematerial-example.html.
> >       • How can I get ModelView matrix in my shader? I need to multiply
> ModelView matrix by vertex to get its current position.
>
> Hi Artem,
>
> The model view matrix is part of the QSGMaterialShader::RenderState that
> is passed in to the QSGMaterialShader::updateState() function which you use
> to apply the state for you material.
>
> >       • How in this example works
> QSGGeometry::defaultAttributes_TexturedPoint2D? What values does it store?
>
> The vertex shader in the code you link only uses a colorized 2D point, one
> vec4 for the position and one vec4 for the color, so you want that kind of
> vertex structure. QSGGeometry::defaultAttributes_ColorizedPoint2D()
> implements that for 2D at least.
>
> >       • How can I pass sourcePoint (the first point of a line) to my
> shader?
>
> It is a uniform, so you write it during the
> QSGMaterialShader::updateState() function.
>
> > If someone knows better way to draw dashed line I would be grateful to
> you for telling me it.
>
> An alternative approach would be to generate the line segments for the
> dashes and combining that with
> QSGGeometry::defaultAttributes_ColorizedPoint2D() and
> QSGVertexColorMaterial. It will be a bit more work to prepare and take up a
> bit more memory, but on the plus side, it will batch in the renderer, so it
> will probably be faster to draw if you have many instances of these dashed
> objects. The modelview/cos based implementation you link to will not
> support batching because each line needs a unique shader state, the model
> view matrix and perhaps also the source point.
>
> cheers,
> Gunnar
>
> >
> > Regards, Artem
> >
> > _______________________________________________
> > Interest mailing list
> > Interest at qt-project.org
> > http://lists.qt-project.org/mailman/listinfo/interest
>
>
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