Loading a fragment shader without loading a vertex shader in GlslProg

in Developing Cinder • 2 years ago

Hi,

I believe there should be a way to load a fragment shader without loading a vertex shader as well. This might be an exotic case, but there are certainly instances in which that would be desirable. Right now, however, this is not possible, as neither constructor of GlslProg accepts NULL as the first argument.

If people agree, I can do the necessary changes.

Alex

Replies(14)

andrewfb

Re: Loading a fragment shader without loading a vertex shader in GlslProg

2 years ago

Hey - I coded it that way because I was under the impression that you cannot have a fragment-only shader - is that incorrect?

alexweiss

Re: Loading a fragment shader without loading a vertex shader in GlslProg

2 years ago

Hey,

I don't know if it's standard or not, but I used a fragment-only shader in my RGB/Lab conversion tool, and it worked just fine...

sansumbre..

Re: Loading a fragment shader without loading a vertex shader in GlslProg

2 years ago

I'm not sure whether it's necessary to have one of each, and the orange book is slightly unclear on the topic. It says a program typically has one of each type, and you can have more than one of each. No word on less than.

In any case, you can use a passthrough shader for the vertex phase to mimic fixed functionality:

void main()

{

gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;

}

andrewfb

Re: Loading a fragment shader without loading a vertex shader in GlslProg

2 years ago

OK - looks like I was wrong:

http://www.opengl.org/registry/specs/ARB/shader_objects.txt

1) What to do if part of a shader pair is not present?

    DISCUSSION: There are several shader types that go together. For
    example, a VERTEX_SHADER and a FRAGMENT_SHADER form a pair that is part
    of the geometry pipeline. It is not required to supply both shader types
    of a pair in a program object.

    RESOLUTION: If one or the other of a pair is not present in the program
    object, OpenGL will substitute the standard 1.4 OpenGL pipeline for the
    one not present.

if someone wants to submit a patch I will roll it in.

alexweiss

Re: Loading a fragment shader without loading a vertex shader in GlslProg

2 years ago

There you go:

http://github.com/awelex/Cinder/commit/09835a28bd6056bc9399b9bf5f19da899acaec70

The only flaw right now is that it is theoretically possible to create a program without any shaders, which is not particularly useful. It's not harmful either, though - I checked.

andrewfb

Re: Loading a fragment shader without loading a vertex shader in GlslProg

2 years ago

Pushed:

http://github.com/cinder/Cinder/commit/a60a75f7529e8ef7377a449c79ce09d427bfcbe7

thanks for the patch...

-Andrew

num3ric

Réf.: Loading a fragment shader without loading a vertex shader in GlslProg

2 years ago

I'm reviving this discussion because this patch has apparently been lost: it's not in the latest version. [EDIT: On further thought, maybe it's a temporary issue due to merging?]

Also, knowing that these are the constructors:

GlslProg( DataSourceRef vertexShader, DataSourceRef fragmentShader = DataSourceRef(), DataSourceRef geometryShader = DataSourceRef() );
GlslProg( const char *vertexShader, const char *fragmentShader = 0, const char *geometryShader = 0 );

How can we declare only a frag shader? Shouldn't the constructors be like this:

GlslProg( DataSourceRef vertexShader= DataSourceRef(), DataSourceRef fragmentShader= DataSourceRef(), DataSourceRef geometryShader =DataSourceRef() );
GlslProg( const char *vertexShader= 0, const char *fragmentShader = 0, const char *geometryShader = 0 );

mShader = gl::GlslProg(loadResource( "frag.glsl" ));

How would it know it's the second argument? I need to learn a more about C++ ...

[ Frag-only shaders are shown to be perfectly useful in the fbodrawbuffer sample in these examples --> http://www.opengl.org/sdk/docs/books/SuperBible/ ]

alexweiss

Réf.: Loading a fragment shader without loading a vertex shader in GlslProg

2 years ago

Hi,

hm, that's weird. I don't see the code changes, either.

However, IF those code changes are added back in, you can simply pass NULL for the other two arguments if you only want to load a fragment shader.

num3ric

Réf.: Loading a fragment shader without loading a vertex shader in GlslProg

2 years ago

Are you sure passing NULL works?

It might work for the GlslProg constructor using char pointers ( GlslProg( const char *vertexShader, const char *fragmentShader = 0, const char *geometryShader = 0 ); ) but not when it's DataSourceRef? I tried it both with 2 and 3 arguments and it didn't work: error: no matching function for call to 'cinder::gl::GlslProg::GlslProg(NULL, cinder::DataSourcePathRef)'

I'm currently using this and I get no errors at compile time:

mPosShader = gl::GlslProg( shared_ptr<DataSourcePath>(), loadResource("pos.frag"));

Is this normal? It's not very intuitive...

andrewfb

Re: Loading a fragment shader without loading a vertex shader in GlslProg

2 years ago

Hey guys - it looks like I might have undone this commit on accident - let me look into that...

-Andrew

andrewfb

Re: Loading a fragment shader without loading a vertex shader in GlslProg

2 years ago

Sorry for the delay - this was my mistake, due to the commit I made removing the Mac's dependency on GLee. This should be back now. Also I am at Siggraph at the moment, and this was confirmed at the OpenGL BoF meeting to be allowed in OpenGL 4.x as well.

-Andrew

letsgoout..

Re: Loading a fragment shader without loading a vertex shader in GlslProg

2 years ago

Is there any performance increase in not using a vertex shader? Or does not loading one essentially result in OpenGL sort of generating a pass-thru vertex shader to insert into the pipeline?

sasmaster

Re: Loading a fragment shader without loading a vertex shader in GlslProg

9 months ago

Weird.I have never used fixed pipeline but in the forward compatible and core profile I am not sure you can compile a program without both vert and frag shaders present .Can you ?

letsgoout..

Re: Loading a fragment shader without loading a vertex shader in GlslProg

9 months ago

I'm pretty sure that's the case because newer OpenGL has no default shader, lights, etc. The vertex structure is user defined.

http://www.BanTheRewind.com

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