to draw a red triangle in openGl using c++ library GLEW [closed] - c++

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I'm trying to draw a red triangle in OpenGL using GLEW. Firstly, I have drawn a triangle at the center of screen. This is getting drawn correctly. Then, I am trying to use shaders to get a red triangle. But, I couldn't get a red triangle because my shader compilation is failing. What could be possibly wrong?
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <iostream>
static unsigned int CompileShader(unsigned int type, const std::string& source)
{
unsigned int id = glCreateShader(type);
const char* src = source.c_str();
glShaderSource(id, 1, &src, nullptr);
glCompileShader(id);
int result;
glGetShaderiv(id, GL_COMPILE_STATUS, &result);
if (result == GL_FALSE)
{
std::cout << "failed to compile shader" << std::endl;
}
return id;
}
static int CreateShader(const std::string& vertexShader, const std::string& fragmentShader)
{
unsigned int program = glCreateProgram();
unsigned int vs = CompileShader(GL_VERTEX_SHADER,vertexShader);
unsigned int fs = CompileShader(GL_FRAGMENT_SHADER,fragmentShader);
glAttachShader(program, vs);
glAttachShader(program, fs);
glLinkProgram(program);
glValidateProgram(program);
glDetachShader(program,vs);
glDetachShader(program,fs);
glDeleteShader(vs);
glDeleteShader(fs);
return program;
}
int main(void)
{
GLFWwindow* window;
/* Initialize the library */
if (!glfwInit())
return -1;
/* Create a windowed mode window and its OpenGL context */
window = glfwCreateWindow(640, 480, "Hello World", NULL, NULL);
if (!window)
{
glfwTerminate();
return -1;
}
/* Make the window's context current */
glfwMakeContextCurrent(window);
if (glewInit() != GLEW_OK) {
std::cout << "error..!!" << std::endl;
}
float positions[6] = {
-0.5f,-0.5f,
0.5f, -0.5f,
0.0f, 0.5f
};
unsigned int buffer;
glGenBuffers(1, &buffer);
glBindBuffer(GL_ARRAY_BUFFER, buffer);
glBufferData(GL_ARRAY_BUFFER, 6 * sizeof(float),positions,GL_STATIC_DRAW);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);
std::string vertexShader =
"#version 330 core\n"
"\n"
"layout(location=0) in vec4 position;\n"
"\n"
"void main()\n"
"{\n"
" gl_Position=position;\n"
"}\n";
std::string fragmentShader =
"#version 330 core\n"
"\n"
"layout(location=0) out vec4 color;\n"
"\n"
"void main()\n"
"{\n"
" color=vec4(1.0,0.0,0.0,1.0)\n"
"}\n";
unsigned int shader = CreateShader(vertexShader,fragmentShader);
glUseProgram(shader);
/* Loop until the user closes the window */
while (!glfwWindowShouldClose(window))
{
/* Render here */
glClear(GL_COLOR_BUFFER_BIT);
glDrawArrays(GL_TRIANGLES,0,3);
/* Swap front and back buffers */
glfwSwapBuffers(window);
/* Poll for and process events */
glfwPollEvents();
}
glfwTerminate();
return 0;
}

Answer 1

The shader compilation fails, because shader there is missing a semicolon after color=vec4(1.0,0.0,0.0,1.0) in the fragment.
If you print the shader info log, then you can find issues like this easily:
glCompileShader(id);
GLint status;
glGetShaderiv( id, GL_COMPILE_STATUS, &status );
if ( status == GL_FALSE )
{
GLint maxLen;
glGetShaderiv( id, GL_INFO_LOG_LENGTH, &maxLen );
std::vector< char >log( maxLen );
GLsizei len;
glGetShaderInfoLog( id, maxLen, &len, log.data() );
std::cout << "compile error:" << std::endl << log.data() << std::endl;
}
Further, I recommend to use Raw string literals:
std::string fragmentShader = R"(
#version 330 core
layout(location=0) out vec4 color;
void main()
{
color=vec4(1.0, 0.0, 0.0, 1.0);
}
)";