Writing a Shader in OpenGL - hls333555/OpenGL GitHub Wiki

Here are the main steps on how to create a vertex shader:

Shader Part

• Construct a shader source, here we use C++11 raw string literals:

  std::string vertexShaderSource = R"(
  	#version 330 core
  	
  	// The location of the position vertex attribute data is 0
  	layout(location = 0) in vec4 position;
  	void main()
  	{
  		gl_Position = position;
  	}
  )";
  

• Create a shader object:

  unsigned int vsId = glCreateShader(GL_VERTEX_SHADER);
  

• Load the shader source into the shader object:

  const char* src = vertexShaderSource.c_str();
  glShaderSource(vsId, 1, &src, nullptr);
  

• Compile the shader object:

  glCompileShader(vsId);
  
  int result;
  glGetShaderiv(vsId, GL_COMPILE_STATUS, &result);
  if(result == GL_FALSE)
  {
      int length;
      glGetShaderiv(vsId, GL_INFO_LOG_LENGTH, &length);
      // Allocate on the stack dynamically
      char* message = (char*)_malloca(length * sizeof(char));
      // Return the information log for the shader object
      glGetShaderInfoLog(vsId,length, &length, message);
      std::cout << "Failed to compile vertex shader!" << std::endl;
      std::cout << message << std::endl;
      glDeleteShader(vsId);
      return 0;
  }
  

Program Part

• Create the program object:

  unsigned int program = glCreateProgram();
  

• Attach shaders to the program object:

  glAttachShader(program, vsId);
  

• Link the program:

  glLinkProgram(program);
  

• Validate the program object:

  // Check to see whether the executables contained in program can execute given the current OpenGL state
  glValidateProgram(program);
  
  int result;
  glGetProgramiv(program, GL_VALIDATE_STATUS, &result);
  if(result == GL_FALSE)
  {
      std::cout << "Failed to validate program!" << std::endl;
      return 0;
  }
  

• Use the program object:

  // Install the program object as part of current rendering state
  glUseProgram(program); // Do not forget this!
  

• Delete the program object at last:

  glDeleteProgram(program);