OpenGL Program Shader Linking Error - c++

Question

I have been working to create a circle based on a shader that changes color periodically. My code prints out a blank window. I decided to set-up some methods to check for errors using GL_LINK_STATUS and it seems that my code is encountering an issue linking the program and the shader.
I did some research into similar issues that people have had but they don't seem to have similar causes.
I have posted my shader code, the driver program(named Priomary) and the Shader Program below.
Vertex Shader
#version 330 core
layout (location = 0) in vec3 pos;
uniform vec2 posOffset;
void main()
{
gl_Position = vec4(pos.x + posOffset.x, pos.y + posOffset.y, pos.z, 1.0);
}
Fragment Shader
#version 330 core
uniform vec4 vertColor;
out vec4 frag_color;
void main()
{
frag_color = vertColor;
}
Shader Program
#include "ShaderProgram.h"
#include <fstream>
#include <iostream>
#include <sstream>
ShaderProgram::ShaderProgram()
: mProgram(0){
}
ShaderProgram::~ShaderProgram()
{
glDeleteProgram(mProgram);
}
bool ShaderProgram::assignShaders(const char* vertFileName, const char* fragFileName)
{
//Shaders output objects called programs that define their relationship and lead to .exe functionality
//assigning pointer to the shader
string vsString = readFile(vertFileName);
string fsString = readFile(fragFileName);
// c_str returns a const char* that points to a null-terminated string (i.e. a C-style string). It is useful when you want to pass the "contents"¹ of an std::string to a function that expects to work with a C-style string.
const GLchar* vsSourcePtr = vsString.c_str();
const GLchar* fsSourcePtr = fsString.c_str();
//creating vertex shader(vs) shader object
GLuint vs = glCreateShader(GL_VERTEX_SHADER);
GLuint fs = glCreateShader(GL_FRAGMENT_SHADER);
//assigning shader source using address. Replaces the source code in a shader object //#arg (shader, count Strings, pointer to const File ,size)
glShaderSource(vs, 1, &vsSourcePtr, NULL);
glShaderSource(fs, 1, &fsSourcePtr, NULL);
glCompileShader(vs);
testShaderCompile(vs);
glCompileShader(fs);
testShaderCompile(fs);
//createProgram returns GLUint which is basically an unsigned int... we will use This Handler to create a program object
mProgram = glCreateProgram();
if (mProgram == 0)
{
std::cerr << "Shader cannot be created" << std::endl;
return false;
}
//assign the program object(mProgram) to the Shader
glAttachShader(mProgram, vs);
glAttachShader(mProgram, fs);
//this method accepts a GLuint "program" . If its an object of type GL_VERTEX_SHADER,
//itll create a .exe that runs on the programmable vertex processor. same goes for geometric and fragment shaders if they were included
//it will also bind all user defined uniform variables and attributes to the program
//The program can then be made part of a defined state by calling useProgram
glLinkProgram(mProgram);
testProgramCompile();
//cleaning up the elements we already used
glDeleteShader(vs);
glDeleteShader(fs);
//clear the identifier lookup map(in this case, there's only one)
mUniformIdentifiers.clear();
return true;
}//end main
//Read the shaderFile. strngstream for reading multiple lines
string ShaderProgram:: readFile(const string& filename) {
std::stringstream strgstream;
std::ifstream file;
try
{
file.open(filename, std::ios::in);
if (!file.fail())
{
strgstream << file.rdbuf();
}
file.close();
}
catch (std::exception ex)
{
std::cerr << "Error: File or File Name Issues" << std::endl;
}
return strgstream.str();
}
//use the Program Object we created in this current state(color)
void ShaderProgram::use()
{
//check if it is not null
if (mProgram > 0)
glUseProgram(mProgram);
}
void ShaderProgram::dumpShaderLog(bool is_shader, GLuint obj)
{
int maxlen = 0;
if (is_shader) glGetShaderiv(obj, GL_INFO_LOG_LENGTH, &maxlen);
else glGetProgramiv(obj, GL_INFO_LOG_LENGTH, &maxlen);
if (maxlen > 0)
{
char *log = new char[maxlen];
int len;
if (is_shader) glGetShaderInfoLog(obj, maxlen, &len, log);
else glGetProgramInfoLog(obj, maxlen, &len, log);
if (len > 0 && log[0] != '\0')
fprintf(stderr, "%s\n", log);
delete[] log;
}
}
void ShaderProgram::testProgramCompile() {
int status = 0;
GLuint program = mProgram;
// ///CHECKING GL_LINK_STATUS to see if Program Link was successul. Link Status will return GL_TRUE if it was
glGetProgramiv( mProgram, GL_LINK_STATUS, &status); //requesting the status
if (status == GL_FALSE)
{
GLint length = 0;
glGetProgramiv(mProgram, GL_INFO_LOG_LENGTH, &length);
string errorLog(length, ' '); // Resize and fill with space character
glGetProgramInfoLog(mProgram, length, &length, &errorLog[0]);
dumpShaderLog(false, mProgram);
std::cerr << "Linking Error with Program and Shader" << std::endl;
}
}
void ShaderProgram :: testShaderCompile(GLuint shader) {
int status = 0;
// ///CHECKING GL_LINK_STATUS to see if Program Link was successul. Link Status will return GL_TRUE if it was
glGetShaderiv (shader, GL_COMPILE_STATUS, &status);//requesting the status
if (status == GL_FALSE)
{
GLint length = 0;
glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &length);
string errorLog(length, ' '); // Resize and fill with space character
glGetShaderInfoLog(shader, length, &length, &errorLog[0]);
std::cerr << "SHADER COMPILE TEST ERROR " << std::endl;
}
}
////GETTERS AND SETTERS
GLuint ShaderProgram::getProgram() const
{
return mProgram;
}
void ShaderProgram::setUniform(const GLchar* name, const glm::vec2& v)
{
GLint address = getUniformIdentifier(name);
glUniform2f(address, v.x, v.y);
}
void ShaderProgram::setUniform(const GLchar* name, const glm::vec3& v)
{
GLint address = getUniformIdentifier(name);
glUniform3f(address, v.x, v.y, v.z);
}
void ShaderProgram:: setUniform(const GLchar* name, const glm::vec4& v) {
GLint address = getUniformIdentifier(name);
glUniform4f(address, v.x, v.y, v.z, v.w);
}
//Maybe need to switch places with setUniform
GLint ShaderProgram :: getUniformIdentifier(const GLchar* name) {
std::map<std::string, GLint>::iterator it;
it = mUniformIdentifiers.find(name);
//std::map<std::string, GLint>
// Only need to query the shader program IF it doesn't already exist.
if (it == mUniformIdentifiers.end())
{
// Find it and add it to the map
mUniformIdentifiers[name] = glGetUniformLocation(mProgram, name);
}
// Return it
return mUniformIdentifiers[name];
}
Primary Program
#include <iostream>
#include <vector>
#include <sstream>
#define GLEW_STATIC
//always GLEW before GLFW
#include "GL/glew.h"
#include "GLFW/glfw3.h"
#include "glm/glm.hpp"
#include "ShaderProgram.h"
#ifndef M_PI
# define M_PI 3.141592653
#endif
/////gLOBAL
GLFWwindow* w = NULL;
const int wWidth = 800;
const int wHeight = 600;
std::vector<glm::vec3> vertices;
std::vector<unsigned int> indices;
GLfloat Radius = 6;
GLfloat Stacks = 5;
GLfloat Slices = 5;
void key_callback(GLFWwindow *w, int key, int scancode, int action, int mode);
//update colors based on average framerate
void averageFPS(GLFWwindow* window);
//screen resizing
void glfw_onFramebufferSize(GLFWwindow* window, int width, int height);
bool initOpenGL();
static void error(int error, const char *desc)
{
fputs(desc, stderr);
}
//setting up values for keys
int main() {
//pointing to GLFW window
//GLFWwindow *w; //may want to initialize as null outside before main
if (!initOpenGL()) ///5IMPR
{
// An error occured
std::cerr << "GLFW not initialized" << std::endl;
return -1;
}
glfwSetErrorCallback(error);
///TEMP CIRCLE VERTICES
// Calc The Vertices
for (int i = 0; i <= Stacks; ++i) {
float V = i / (float)Stacks;
float phi = V * M_PI; //change to glm:: pi
// Loop Through Slices
for (int j = 0; j <= Slices; ++j) {
float U = j / (float)Slices;
float theta = U * (M_PI * 2);
// Calc The Vertex Positions
float x = cosf(theta) * sinf(phi);
float y = cosf(phi);
float z = sinf(theta) * sinf(phi);
// Push Back Vertex Data //push_back is a standard vector function which adds a parameter to the end of the vector
//std::vector<glm::vec3> vertices; //moved to global variables at top
vertices.push_back(glm::vec3(x, y, z) * Radius);
}
}
// Calc The Index Positions
for (int i = 0; i < Slices * Stacks + Slices; ++i) {
indices.push_back(i);
indices.push_back(i + Slices + 1);
indices.push_back(i + Slices);
indices.push_back(i + Slices + 1);
indices.push_back(i);
indices.push_back(i + 1);
}
////TEMP CIRCLE VERTICES END
// 2. Set up buffers on the GPU
GLuint vbo, ibo, vao; ///5IMPROVEdown
glGenBuffers(1, &vbo); // Generate an empty vertex buffer on the GPU
glBindBuffer(GL_ARRAY_BUFFER, vbo); // "bind" or set as the current buffer we are working with
//3rd argument of glBufferData needs a pointer to the std:vector data...A pointer to the data can be obtained by vertices.data() accrding to std: ector docs...
glBufferData(GL_ARRAY_BUFFER, vertices.size() * sizeof(glm::vec3), vertices.data(), GL_STATIC_DRAW);// copy the data from CPU to GPU
glGenVertexArrays(1, &vao); // Tell OpenGL to create new Vertex Array Object
glBindVertexArray(vao); // Make it the current one
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, NULL); // Define a layout for the first vertex buffer "0"
glEnableVertexAttribArray(0); // Enable the first attribute or attribute "0"
// Set up index buffer
glGenBuffers(1, &ibo); // Create buffer space on the GPU for the index buffer
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, indices.size() * sizeof(unsigned int), indices.data(), GL_STATIC_DRAW);
// glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW); - REPLACED
glBindVertexArray(0); // unbind to make sure other code doesn't change it
ShaderProgram shaderProgram; ///5ADD
shaderProgram.assignShaders("shaders\\ColorShader.vert", "shaders\\ColorShader.frag"); ///5ADD
////////SETUP RENDERING
while (!glfwWindowShouldClose(w))
{
averageFPS(w);
//process events
glfwPollEvents();
// Clear the screen
glClear(GL_COLOR_BUFFER_BIT);
shaderProgram.use(); ///5ADD
GLfloat time = (GLfloat)glfwGetTime(); ///5ADD
GLfloat blueSetting = (sin(time) / 2) + 0.5f; ///5ADD
glm::vec2 pos;
pos.x = sin(time) / 2;
pos.y = cos(time) / 2;
shaderProgram.setUniform("vertColor", glm::vec4(0.0f, 0.0f, blueSetting, 1.0f)); ///5ADD
shaderProgram.setUniform("posOffset", pos);
glBindVertexArray(vao);
//og for quad
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
//glDrawElements(GL_LINE_LOOP, 6, GL_UNSIGNED_INT, 0);
glBindVertexArray(0);
// Swap buffers and look for events
glfwSwapBuffers(w);
}
//clean up
glDeleteVertexArrays(1, &vao);
glDeleteBuffers(1, &vbo);
glDeleteBuffers(1, &ibo);
//glfwDestroyWindow(w);
glfwTerminate();
return 0;
}
///////START Initializing glfw glew etc
bool initOpenGL(){
//this method will exit on these conditions
GLuint error = glfwInit();
if (!error)
return false;
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
w = glfwCreateWindow(wWidth, wHeight, "Exercise", NULL, NULL);
if (w== NULL)
{
std::cerr << "glfw window not created" << std::endl;
glfwTerminate();
return false;
}
//update context
glfwMakeContextCurrent(w);
// Initialize GLEWunifor
glewExperimental = GL_TRUE;
GLuint err = glewInit();
if (err != GLEW_OK)
{
std::cerr << "initialize GLEW Failed" << std::endl;
return false;
}
//setup key callbacks
glfwSetKeyCallback(w, key_callback);
glfwSetFramebufferSizeCallback(w, glfw_onFramebufferSize);
glClearColor(0.23f, 0.38f, 0.47f, 1.0f); ///5ADD
// Define the viewport dimensions
glViewport(0, 0, wWidth, wHeight); //necessary?
return true;
}
void key_callback(GLFWwindow *w, int key, int scancode, int action, int mode)
{
// See http://www.glfw.org/docs/latest/group__keys.html
if ((key == GLFW_KEY_ESCAPE || key == GLFW_KEY_Q) && action == GLFW_PRESS)
glfwSetWindowShouldClose(w, GL_TRUE);
if (key == GLFW_KEY_W && action == GLFW_PRESS)
{
bool showWires = false;
if (showWires)
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
else
glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
}
}
//whever window resizes, do this
void glfw_onFramebufferSize(GLFWwindow* window, int width, int height)
{
glViewport(0, 0, width, height);
}
void averageFPS(GLFWwindow* window) ///5ADDdown
{
static double previousSeconds = 0.0;
static int frameCount = 0;
double passedSeconds;
double currentSeconds = glfwGetTime(); //seconds since GLFW started
passedSeconds = currentSeconds - previousSeconds;
// Limit time updates to 4 times per second
if (passedSeconds > 0.25)
{
previousSeconds = currentSeconds;
double fps = (double)frameCount / passedSeconds;
// double frameInMilSecs = 1000.0 / fps;
frameCount = 0;}
frameCount++;
}

Answer 1

While glGetShaderiv returns a parameter from a shader object, glGetProgramiv returns a parameter from a program object.
This means you have to change your code like this:
// glGetProgramiv(shader, GL_COMPILE_STATUS, &status); <--- delete
glGetShaderiv (shader, GL_COMPILE_STATUS, &status);
Ensure that the shader files are correctly loaded and trace them for debug reasons:
glShaderSource(vs, 1, &vsSourcePtr, NULL);
glShaderSource(fs, 1, &fsSourcePtr, NULL);
std::cout << "VERTEX SHADER:" << std::endl << vsSourcePtr << std::endl << std::endl;
glCompileShader(vs);
testShaderCompile(vs);
std::cout << "FRAGMENT SHADER:" << std::endl << fsSourcePtr << std::endl << std::endl;
glCompileShader(fs);
testShaderCompile(fs);
Since you don't set any matrices, you have to set up all the vertex coordinates in normalized device space, which is in [-1.0, 1.0].
To make the mesh proper "visible" on the viewport set the radius of the sphere to 0.5:
GLfloat Radius = 0.5f;
and draw all the primitives:
glDrawElements(GL_TRIANGLES, indices.size(), GL_UNSIGNED_INT, 0);