[2.1] Geometry Shader Line Adjacency

Problems building or running the engine, queries about how to use features etc.
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gabbsson
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[2.1] Geometry Shader Line Adjacency

Post by gabbsson » Tue Oct 30, 2018 4:24 pm

Render System: GL3Plus

Hello!

I'm writing a geometry shader to create lines of a given thickness.
Currently I have a solution which lets me set thickness and it works fine, example:
Image

As you can see there are gaps between line segments due to how the expansion is done (normal to the line).
I have found plenty of examples on how to remedy this, but it requires that the shader knows about adjacent lines.
This seems to be a fairly common concept, as it is possible to "request" lines_adjacency in the geometry shader.

If I have understood correctly this should give me 4 vertices (3 line segments) instead of the usual 2 (single line segment).
The indexes are now: 0 - prev segment start, 1 - prev end/current start, 2 - current end/next start, 3 - next end.

I have tried to set the input layout: layout(lines_adjacency) and adjusted my indexes accordingly, but the line is not rendered.
To clarify: I am trying to switch from lines to lines_adjacency and do nothing new with the information, just render as before using the new indexes.
It does not complain about the indexing (as it would if I try to access an index above 1 for lines without adjacency).

A quick search through the Ogre source showed that the render system should detect if adjacency is needed or not (OgreGL3PlusRenderSystem.cpp line 2539):

Code: Select all

// Use adjacency if there is a geometry program and it request adjacency info.
bool useAdjacency  = (mGeometryProgramBound && mPso->geometryShader && mPso->geometryShader->isAdjacencyInfoRequired());
Unfortunately I am stuck here and don't know how to debug this.
There is a reference to adjacency in the manual which should be set using material scripts, I am not using material scripts (since switching to 2.1) at all, are they required?

I would add more information if I knew what else to try, will supply any information you need just ask!
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gabbsson
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Re: [2.1] Geometry Shader Line Adjacency

Post by gabbsson » Fri Nov 02, 2018 8:42 am

Perhaps I can rephrase the question to: is there a good way to know if the rendersystem is currently using adjacency information for my shader?
That way I could figure out if I am doing something wrong in the shader or if the shader is not getting the correct information.

Edit:
My geometry shader is defined in the HLMS folder for (a version) of Unlit.
Not sure how to consolidate that with material/program scripts. I see plenty of examples in the samples for scripts but there are not present in the samples hlms folder.
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