Can't link shaders to program object in OpenGL, can't debug - c++

Question

I attach a vertex and fragment shader to a program object, then attempt to link the said program. GL_LINK_STATUS returns false. I check the info log, it's a bunch of gibberish characters. I check GL_INFO_LOG_LENGTH, it's 0. How do I debug this situation?
//this is the end of my LoadBasicShaders function
glAttachShader(program, vertShader);
glAttachShader(program, fragShader);
glLinkProgram(program);
GLint status;
glGetProgramiv(program, GL_LINK_STATUS, &status);
if (status == GL_FALSE)
{
GLint logLength = 0;
glGetProgramiv(program, GL_INFO_LOG_LENGTH, &logLength);
std::vector<GLchar> log(logLength + 1);
glGetProgramInfoLog(program, logLength, &logLength, &log[0]);
fprintf(stderr, "%s\n\n", log);
//logLength returns 0, log returns seemingly random chars
return -3;//just my error code
}
My shaders are the simplest ones possible, since I'm just starting out.
Here's the vertex shader:
#version 330
layout(location = 0) in vec4 position;
void main()
{
gl_Position = position;
}
And here's the fragment shader:
#version 330
out vec4 outputColor;
void main()
{
outputColor = vec4(1.0, 1.0, 1.0, 1.0);
}
I use GLFW to create the OpenGL window, and GLEW to load the functions:
if (!glfwInit())
{/*error checking*/}
window = glfwCreateWindow(800, 600, "Swash", NULL, NULL);
if (!window)
{/*more error checking*/}
glfwMakeContextCurrent(window);
glfwSwapInterval(1);
glfwSetKeyCallback(window, key_callback);
if (glewInit() != GLEW_OK)
{/*you guessed it*/}
//don't call anything that involves nonstandard OpenGL functions before this point
GLuint shaderProgram;
int shaderLoadResult = LoadBasicShaders(shaderProgram, "../res/vert.shader", "../res/frag.shader");

Answer 1

Use the GLFW error callback
Bullet-proof your shader loader
Use ARB_debug_output or KHR_debug
Request an explicit GL version and profile (Core/Compatibility) via glfwWindowHint()
All together (this is what I meant by posting a MCVE):
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <iostream>
#include <cstdlib>
struct GlDebugOutput
{
static void Install()
{
if( !glewIsSupported( "GL_ARB_debug_output" ) )
{
std::cerr << "GL_ARB_debug_output not supported" << std::endl;
return;
}
glEnable( GL_DEBUG_OUTPUT_SYNCHRONOUS_ARB );
glDebugMessageCallbackARB( DebugCallback, 0 );
glDebugMessageControlARB( GL_DONT_CARE, GL_DONT_CARE, GL_DONT_CARE, 0, NULL, GL_TRUE );
}
private:
static const char* Source( GLenum source )
{
switch( source )
{
case GL_DEBUG_SOURCE_API_ARB : return "API";
case GL_DEBUG_SOURCE_WINDOW_SYSTEM_ARB : return "WINDOW_SYSTEM";
case GL_DEBUG_SOURCE_SHADER_COMPILER_ARB : return "SHADER_COMPILER";
case GL_DEBUG_SOURCE_THIRD_PARTY_ARB : return "THIRD_PARTY";
case GL_DEBUG_SOURCE_APPLICATION_ARB : return "APPLICATION";
case GL_DEBUG_SOURCE_OTHER_ARB : return "OTHER";
default : return "Unknown source";
}
}
static const char* Type( GLenum type )
{
switch( type )
{
case GL_DEBUG_TYPE_ERROR_ARB : return "ERROR";
case GL_DEBUG_TYPE_DEPRECATED_BEHAVIOR_ARB : return "DEPRECATED_BEHAVIOR";
case GL_DEBUG_TYPE_UNDEFINED_BEHAVIOR_ARB : return "UNDEFINED_BEHAVIOR";
case GL_DEBUG_TYPE_PORTABILITY_ARB : return "PORTABILITY";
case GL_DEBUG_TYPE_PERFORMANCE_ARB : return "PERFORMANCE";
case GL_DEBUG_TYPE_OTHER_ARB : return "OTHER";
default : return "Unknown type";
}
}
static const char* Severity( GLenum severity )
{
switch( severity )
{
case GL_DEBUG_SEVERITY_HIGH_ARB : return "HIGH";
case GL_DEBUG_SEVERITY_MEDIUM_ARB : return "MEDIUM";
case GL_DEBUG_SEVERITY_LOW_ARB : return "LOW";
default : return "Unknown severity";
}
}
static void APIENTRY DebugCallback
(
GLenum source,
GLenum type,
GLuint id,
GLenum severity,
GLsizei length,
const GLchar* message,
const void* userParam
)
{
std::cerr << "GL_DEBUG"
<< ": " << Source( source )
<< ": " << Type( type )
<< ": " << Severity( severity )
<< ": " << message
<< std::endl;
}
};
struct Program
{
static GLuint Load( const char* vert, const char* geom, const char* frag )
{
GLuint prog = glCreateProgram();
if( vert ) AttachShader( prog, GL_VERTEX_SHADER, vert );
if( geom ) AttachShader( prog, GL_GEOMETRY_SHADER, geom );
if( frag ) AttachShader( prog, GL_FRAGMENT_SHADER, frag );
glLinkProgram( prog );
CheckStatus( prog );
return prog;
}
private:
static void CheckStatus( GLuint obj )
{
GLint status = GL_FALSE;
if( glIsShader(obj) ) glGetShaderiv( obj, GL_COMPILE_STATUS, &status );
if( glIsProgram(obj) ) glGetProgramiv( obj, GL_LINK_STATUS, &status );
if( status == GL_TRUE ) return;
GLchar log[ 1 << 15 ] = { 0 };
if( glIsShader(obj) ) glGetShaderInfoLog( obj, sizeof(log), NULL, log );
if( glIsProgram(obj) ) glGetProgramInfoLog( obj, sizeof(log), NULL, log );
std::cerr << log << std::endl;
exit( EXIT_FAILURE );
}
static void AttachShader( GLuint program, GLenum type, const char* src )
{
GLuint shader = glCreateShader( type );
glShaderSource( shader, 1, &src, NULL );
glCompileShader( shader );
CheckStatus( shader );
glAttachShader( program, shader );
glDeleteShader( shader );
}
};
#define GLSL(version, shader) "#version " #version "\n" #shader
const char* vert = GLSL
(
330,
layout( location = 0 ) in vec4 position;
void main()
{
gl_Position = position;
}
);
const char* frag = GLSL
(
330,
out vec4 outputColor;
void main()
{
outputColor = vec4( 1.0, 1.0, 1.0, 1.0 );
}
);
GLuint VAO;
GLuint VBO;
GLuint prog;
void init()
{
glGenVertexArrays( 1, &VAO );
glBindVertexArray( VAO );
glGenBuffers( 1,&VBO );
glBindBuffer( GL_ARRAY_BUFFER, VBO );
float verts[] =
{
-1.0, -1.0,
1.0, -1.0,
0.0, 1.0,
};
glBufferData( GL_ARRAY_BUFFER, sizeof( verts ), verts, GL_STATIC_DRAW );
prog = Program::Load( vert, NULL, frag );
glUseProgram( prog );
glEnableVertexAttribArray( 0 );
glVertexAttribPointer( 0, 2, GL_FLOAT, GL_FALSE, 0, 0 );
}
void display()
{
glClearColor( 0, 0, 0, 1 );
glClear( GL_COLOR_BUFFER_BIT );
glUseProgram( prog );
glBindVertexArray( VAO );
glDrawArrays( GL_TRIANGLES, 0, 3 );
}
void glfwErrorCallback( int error, const char* description )
{
std::cerr << "GLFW error: " << description << std::endl;
}
int main( int argc, char** argv )
{
glfwSetErrorCallback( glfwErrorCallback );
if( GL_FALSE == glfwInit() )
{
return EXIT_FAILURE;
}
std::cout << "GLFW version : " << glfwGetVersionString() << std::endl;
glfwWindowHint( GLFW_CONTEXT_VERSION_MAJOR, 3 );
glfwWindowHint( GLFW_CONTEXT_VERSION_MINOR, 3 );
glfwWindowHint( GLFW_OPENGL_PROFILE, GLFW_OPENGL_COMPAT_PROFILE );
glfwWindowHint( GLFW_OPENGL_DEBUG_CONTEXT, GL_TRUE );
GLFWwindow* window = glfwCreateWindow( 640, 480, "Test", NULL, NULL );
if( NULL == window )
{
glfwTerminate();
return EXIT_FAILURE;
}
glfwMakeContextCurrent( window );
glfwSwapInterval( 1 );
glewExperimental = GL_TRUE;
const GLenum glewErr = glewInit();
if( GLEW_OK != glewErr )
{
std::cerr << "glewInit() failed: " << glewGetErrorString( glewErr ) << std::endl;
glfwTerminate();
return EXIT_FAILURE;
}
// consume spurious GL error from GLEW init
glGetError();
GlDebugOutput::Install();
init();
while( !glfwWindowShouldClose( window ) )
{
glfwPollEvents();
int w, h;
glfwGetFramebufferSize( window, &w, &h );
glViewport( 0, 0, w, h );
display();
glfwSwapBuffers( window );
}
return EXIT_SUCCESS;
}
If anything is even just a little bit off with your OpenGL implementation and/or shaders that program should scream bloody murder to stderr and exit.

Answer 2

Sorry for the very slow update, I've been busy with other things.
Anyways, the problem was that while writing the code, I had included the line
program = glCreateProgram();
but at some point, while tidying up, I accidentally deleted it. That's why the shaders were compiling but weren't linking, they weren't being linked to a program object.