Shader program linking issue

Kametec Housen · 2013-05-11T17:35:35

Hi, I'm getting started with OpenGL. I'm trying to get my first program working, but I have no luck so far and I have no idea why. My test program is inspired by the first program in a book named "OpenGL Programming Guide, The Official Guide to Learning OpenGL, Version 4.3, Eight Edition". I've written both vertex and fragment shaders, I've written code to initialize FreeGlut, GLEW, compile the shaders and link the shader program. But I have issues with the linking proccess. The output of glGetProgramInfoLog is this: Vertex shader(s) failed to link, fragment shader(s) failed to link. Vertex link error: INVALID_OPERATION. ERROR: error(#97) No program main found fragment link error: INVALID_OPERATION. ERROR: error(#97) No program main found I've written definition of my shaders into files, their contents are: Vertex shader in triangles.vert: #version 400 core layout(location = 0) in vec4 vPosition; void main() { gl_Position = vPosition; } Fragment shader in triangles.frag: #version 400 core out vec4 fColor; void main() { fColor = vec4(0.0, 0.0, 1.0, 1.0); } I believe that the error suggests that there is something wrong with my shaders, but I don't know what. Both have void main() present. For completeness' sake I include my C++ program which takes care about compiling and linking the shaders: int main(int argc, char** argv) { GLuint vShad,fShad,prg; GLchar **str = new GLchar*[1]; GLubyte i; GLchar c; GLint err; str[0] = new GLchar[256]; for (i=0; i<255;i++) str[0] = NULL; str[0][255] = NULL; i = 0; glutInit(&argc, argv); glutInitDisplayMode(GLUT_RGBA); glutInitWindowSize(512,512); glutInitContextVersion(4,0); glutInitContextProfile(GLUT_CORE_PROFILE); glutCreateWindow(argv[0]); if (glewInit()) return -1; //Code omitted: vertices and buffers //vertex shader std::ifstream ifs("F:\\dev\\project\\test\\test\\triangles.vert"); while (ifs.get(c)) //Reading contents of the file into GLchar** { str[0] = c; i++; } vShad = glCreateShader(GL_VERTEX_SHADER); glShaderSource(vShad,1,(const char **)str,NULL); glCompileShader(vShad); glGetShaderiv(vShad,GL_COMPILE_STATUS,&err); if (err == GL_FALSE) { //Code omitted: Fetching compiler log return 1; } //fragment shader for (i=0; i<255;i++) str[0] = NULL; str[0][255] = NULL; i = 0; ifs.open("F:\\dev\\project\\test\\test\\triangles.frag"); while (ifs.get(c)) //Reading contents of the file into GLchar** { str[0] = c; i++; } fShad = glCreateShader(GL_FRAGMENT_SHADER); glShaderSource(fShad,1,(const char **)str,NULL); glCompileShader(fShad); glGetShaderiv(fShad,GL_COMPILE_STATUS,&err); if (err == GL_FALSE) { //Code omitted: Fetching compiler log return 2; } //shader program prg = glCreateProgram(); glAttachShader(prg,vShad); glAttachShader(prg,fShad); glLinkProgram(prg); glGetProgramiv(prg,GL_LINK_STATUS,&err); if (err == GL_FALSE) { //Code omitted: Fetching linker log return 3; } glUseProgram(prg); //Code omitted return 0; } A few notes: I had to reduce #version 430 core to #version 400 core, because FreeGlut couldn't initialize OpenGL 4.3 context on my hardware. I am sure that shaders are compiled successfully. My main() returns 3, indicating an error with linking. I have omitted code which I believe to be irrelevant to my issue. Both FreeGlut and GLEW are initialized. I'm using MS Visual Studio 2010 Express, FreeGlut 2.8.1 and GLEW 1.9.0. I would be really grateful for any advice on where should I check for error and what kind of error might that be. Thanks in advance. edit: Code omitted comments are now in right places. edit2: Glut window, profile and context initialization code included, unnecessary empty lines in code removed edit3: Code responsible for reading files updated

Graphics and GPU Programming Programming OpenGL

Started by Kametec May 09, 2013 07:45 AM

10 comments, last by Kametec 10 years, 12 months ago

Sponji

2,505

May 10, 2013 09:00 PM

Are you really sure that the shaders are correct? Why you're doing stuff like this:


GLchar **str = new GLchar*[1];

Not sure how that pointer works, too sleepy. I'd probably write it like this, much simpler:


char *str = new char[256]; 
memset(str, 0, 256);
readvertexshader();
memset(str, 0, 256);
readfragmentshader();
// ...
glShaderSource(fShad, 1, (const char**)&str, NULL);
// and now you can really make sure that you have the actual shader source there, just print it out
printf("shader source:\n%s\n", str);

Actually... I think you should have written (const char**)&str[1] before, because of that weird pointer thingie you were doing. I tried your code on my computer and seemed to work ok with those changes, had to change version numbers too though, my card doesn't support OpenGL 4.0.

Edit: And oh, seemed like I had to call ifs.close() too, not sure if this is only like this on Linux? I think it clears the eof bit, too lazy to check out. Sleep I goes.

Derp

Kametec

134

Author

May 11, 2013 05:35 PM

Hi,

thanks for your reply, it helped me to solve the problem. The error was caused by missing ifs.close(), and the second shader wasn't read correctly because of it.

As to why I used GLchar **str, well, I'm starting to learn C++ as well as OpenGL. I have some experience with other languages, though. I've read in documentaion that glShaderSource accepts GLchar **, so I declared my variable as GLchar **. Thinking of it as two-dimensional array helped me to get it running.

Now, that I am familiar with & and * operators I admit you're right, and I will use an array of GLchar passed as &arr_name in future code.

In summary: I've included ifs.close() and the whole issue dissapeared. I didn't do anything else, so I managed to get file reading to work properly.

Thanks again.

Shader program linking issue

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Shader program linking issue

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