Skip to main content
gamedev.net
🔒 Locked

GLSL Problem

OpenGL
Started by hcpizzi 9 replies 2.2k views
Original Post
hcpizzi
hcpizzi
Hi, I'm doing some stuff using GLSL, and I'm facing some problems. First, when I first tried to compile a simple fragment sahder, one that only outputs a constant color: void main() { gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0); } the compiler raised an error on the identifier void. But if I insert a blank line before the void main() line, it compiles OK. Well, that's annoying, but I could solve it. Now, I add this compiled shader to a program, and try to link it. The linker then rises an error saying that "Not all shaders have valid object code". There's no place I have found where I can check what this quite ambiguous message means, and I guess it's driver/vendor specific. I'm using an ATI Radeon 9800 SE with latest Catalyst 4.10 drivers. OpenGL version, as returned by glGetString, is 1.5.4650 WinXP Release, and GLSL version is 1.00. Anyone has any clue why this may be happening? May this be because I'm not adding a vertex shader to the program? If I have understood documentation, there's no need for a program to contain both vertex and fragment shaders, defaulting to fixed functionality for absent shaders. One last clue: this same behaviour happens if I rename the main function with another name: shader compiles OK, but program fails to link with the same error message. But this makes sense, because fragment shader has no entry point. Thank you all.
BlackBox
BlackBox
Well here are some pointers:

1) Yes you need a vertex shader to translate your vertices. for example:

void main(void)
{
gl_Position = ftransform();
}

This should do the job just fine!

2) In your fragment program you are forgeting the void:
void main(void)
{
...
}

Maybe void will fix the problem.


Let me know if that works.
BTW you can always use RenderMonkey or Shader Designer to test your shaders.

---------------------------- ^_^
ehmdjii
ehmdjii
i was wondering, how did you get the version of GLSL?
hcpizzi
hcpizzi
I'll try adding a vertex shader, but I thought that if a vertex shader was missing, fixed pipeline would be used instead.

I tried adding void as param for main, but didn't work either.

I got GLSL version by calling:

glGetString(GL_SHADING_LANGUAGE_VERSION_ARB);
zedzeek
zedzeek
>>Anyone has any clue why this may be happening? May this be because I'm not adding a vertex shader to the program? If I have understood documentation, there's no need for a program to contain both vertex and fragment shaders, defaulting to fixed functionality for absent shaders.<<

as blackbox saiz u need a vertex shader,
from the spec u can

vertex program + NO fragment program == OK
vertex program + fragment program == OK
no vertex program + fragment program == NOT OK

hcpizzi
hcpizzi
I've tried adding a vertex shader, but same result: both sahders compile ok, but program fails with the aforementioned message.
hcpizzi
hcpizzi
OK, I found out what was going wrong.

I was passing each line of the source as a separate string. Now I have passed the whole source in one string and it has worked.

Oh, and yes, it is possible to have a fragment shader without a vertex shader.

But now my question is: why the glSetShaderSoureARB function takes several strings as input?

Thank you all!
rick_appleton
rick_appleton
the functions takes several strings as input, so you can create 'generic' functions (eg for lighting) and 'link' the one you want.

You could create a fragment shader which calls a 'lightme' function to return the color of the fragment due to lighting only. You could then create two files, one in which 'lighme' calculates the color with only a single light and the other in which 'lightme' can handle 4 lights. Then during compilation you can 'link' the file you want, without needing to change the rest of the fragment shader file.
hcpizzi
hcpizzi
Yeah, rigth, that makes sense.

But, isn't it more elegant to create a shader object for every shader file, add all of them to the program and link them together to achieve the same result?

I personally prefer this approach of a one-to-one relationship between shader files and shader objects, but I guess other people may prefer the first.
rick_appleton
rick_appleton
Well maybe, but remember that those 'helper' files do nothing by themselves. There is no main function, thus shaderobjects can not be created from them alone.

I just think of it as a kind of #include mechanism.
hcpizzi
hcpizzi
Yes, reading the documentation I found that the predefined __FILE__ macro is the string number, so that matches your argument.

But now, I wonder what the compiler does, because a shader with source "{" compiled just fine.

Topic Locked

This topic has been locked by a moderator. New replies are not allowed.

Sign in to reply to this topic.