A Simple C++ OpenGL Shader Loader – Improved

I wrote one back in 2013, but I’ve learnt some things since then, so I’ve re-written it all with some changes. You can still load/compile shaders from strings or files, and then link/validate/use the resulting shader programs, only this time its all a little bit cleaner and more robust.

The main deficiencies of the previous incarnation were:

  • The Shader class wasn’t required for what I was using this stuff for, so I stripped it out – now you just create a ShaderProgram directly,
  • Error logs weren’t shown for any shader or shader program errors,
  • The shader program didn’t get validated,
  • Abuse of exit(-1) rather than throwing unchecked runtime_errors,
  • Inclusion of using clauses in headers, and
  • Possible wonky static declaration and initialisation of const_iterator error in uniform location getter meant that it might have only “got” the uniform location correcty on first run, when the const_iterator was declared – but in practice I haven’t seen any issues, perhaps because I spotted and fixed it but forgot to update article though…

Anyway, below is an improved version that fixes all of the above – here’s how you use it…


// Start by declaring a pointer to a ShaderProgram. A ShaderProgram can only be instantiated when there
// is a valid OpenGL context (i.e. window) - so you may like to declare the ShaderProgram globally, then
// instantiate it later on when you have an OpenGL context.
ShaderProgram *shaderProgram;
// ...later on when we have a OpenGL context...
shaderProgram = new ShaderProgram();
// To provide the source code for the vertex and fragment shaders you can either initialise from strings or from files:
shaderProgram->initFromStrings(vertexShaderString, fragmentShaderString);
shaderProgram->initFromFiles(vertexShaderFilename, fragmentShaderFilename);
// Add attributes to suit
// Add uniforms to suit
// Enable attributes
// 1.) Create and bind to a vertex array object (VAO)...
// 2.) Create and bind to a vertex buffer object (VBO) and specify your vertex attrib pointers
// 3.) Provide geometry data then unbind from the VBO
// --- Now you can enable vertex attributes with, for example:
             glEnableVertexAttribArray( shaderProgram->attribute("vertexLocation") );
             glEnableVertexAttribArray( shaderProgram->attribute("vertexColour") );
// 5.) Unbind from VAO
// Finally, to draw the geometry using the shader program you can use code similar to this:
// Note: This code assumes you're using GLM for your matrices, modify as appropriate if not. Also
// note that to use glm::value_ptr you must "#include <glm/gtc/type_ptr.hpp>"
             glUniformMatrix4fv(shaderProgram->uniform("mvpMatrix"), 1, GL_FALSE, glm::value_ptr(mvpMatrix) );
             <YOUR-DRAW-CALL-HERE> i.e. glDrawArrays(GL_TRIANGLES, 0, 100) etc.

ShaderProgram Class Source Code

Here’s the code for the class itself:

author     : r3dux
version    : 0.3 - 15/01/2014
description: Gets GLSL source code either provided as strings or can load from filenames,
             compiles the shaders, creates a shader program which the shaders are linked
             to, then the program is validated and is ready for use via myProgram.use(),
             <draw-stuff-here> then calling myProgram.disable();
             Attributes and uniforms are stored in <string, int> maps and can be added
             via calls to addAttribute(<name-of-attribute>) and then the attribute
             index can be obtained via myProgram.attribute(<name-of-attribute>) - Uniforms
             work in the exact same way.
#include <iostream>
#include <fstream>
#include <sstream>
#include <map>
class ShaderProgram
	// static DEBUG flag - if set to false then, errors aside, we'll run completely silent
	static const bool DEBUG = true;
	// We'll use an enum to differentiate between shaders and shader programs when querying the info log
	enum class ObjectType
	// Shader program and individual shader Ids
	GLuint programId;
	GLuint vertexShaderId;
	GLuint fragmentShaderId;
	// How many shaders are attached to the shader program
	GLuint shaderCount;
	// Map of attributes and their binding locations
	std::map<std::string, int> attributeMap;
	// Map of uniforms and their binding locations
	std::map<std::string, int> uniformMap;
	// Has this shader program been initialised?
	bool initialised;
	// ---------- PRIVATE METHODS ----------
	// Private method to compile a shader of a given type
	GLuint compileShader(std::string shaderSource, GLenum shaderType)
		std::string shaderTypeString;
		switch (shaderType)
				shaderTypeString = "GL_VERTEX_SHADER";
				shaderTypeString = "GL_FRAGMENT_SHADER";
				throw std::runtime_error("Geometry shaders are unsupported at this time.");
				throw std::runtime_error("Bad shader type enum in compileShader.");
		// Generate a shader id
		// Note: Shader id will be non-zero if successfully created.
		GLuint shaderId = glCreateShader(shaderType);
		if (shaderId == 0)
			// Display the shader log via a runtime_error
			throw std::runtime_error("Could not create shader of type " + shaderTypeString + ": " + getInfoLog(ObjectType::SHADER, shaderId) );
		// Get the source string as a pointer to an array of characters
		const char *shaderSourceChars = shaderSource.c_str();
		// Attach the GLSL source code to the shader
		// Params: GLuint shader, GLsizei count, const GLchar **string, const GLint *length
		// Note: The pointer to an array of source chars will be null terminated, so we don't need to specify the length and can instead use NULL.
		glShaderSource(shaderId, 1, &shaderSourceChars, NULL);
		// Compile the shader
		// Check the compilation status and throw a runtime_error if shader compilation failed
		GLint shaderStatus;
		glGetShaderiv(shaderId, GL_COMPILE_STATUS, &shaderStatus);
		if (shaderStatus == GL_FALSE)
			throw std::runtime_error(shaderTypeString + " compilation failed: " + getInfoLog(ObjectType::SHADER, shaderId) );
			if (DEBUG)
				std::cout << shaderTypeString << " shader compilation successful." << std::endl;
		// If everything went well, return the shader id
		return shaderId;
	// Private method to compile/attach/link/verify the shaders.
	// Note: Rather than returning a boolean as a success/fail status we'll just consider
	// a failure here to be an unrecoverable error and throw a runtime_error.
	void initialise(std::string vertexShaderSource, std::string fragmentShaderSource)
		// Compile the shaders and return their id values
		vertexShaderId   = compileShader(vertexShaderSource,   GL_VERTEX_SHADER);
		fragmentShaderId = compileShader(fragmentShaderSource, GL_FRAGMENT_SHADER);
		// Attach the compiled shaders to the shader program
		glAttachShader(programId, vertexShaderId);
		glAttachShader(programId, fragmentShaderId);
		// Link the shader program - details are placed in the program info log
		// Once the shader program has the shaders attached and linked, the shaders are no longer required.
		// If the linking failed, then we're going to abort anyway so we still detach the shaders.
		glDetachShader(programId, vertexShaderId);
		glDetachShader(programId, fragmentShaderId);
		// Check the program link status and throw a runtime_error if program linkage failed.
		GLint programLinkSuccess = GL_FALSE;
		glGetProgramiv(programId, GL_LINK_STATUS, &programLinkSuccess);
		if (programLinkSuccess == GL_TRUE)
			if (DEBUG)
				std::cout << "Shader program link successful." << std::endl;
			throw std::runtime_error("Shader program link failed: " + getInfoLog(ObjectType::PROGRAM, programId) );
		// Validate the shader program
		// Check the validation status and throw a runtime_error if program validation failed
		GLint programValidatationStatus;
		glGetProgramiv(programId, GL_VALIDATE_STATUS, &programValidatationStatus);
		if (programValidatationStatus == GL_TRUE)
			if (DEBUG)
				std::cout << "Shader program validation successful." << std::endl;
			throw std::runtime_error("Shader program validation failed: " + getInfoLog(ObjectType::PROGRAM, programId) );
		// Finally, the shader program is initialised
		initialised = true;
	// Private method to load the shader source code from a file
	std::string loadShaderFromFile(const std::string filename)
		// Create an input filestream and attempt to open the specified file
		std::ifstream file( filename.c_str() );
		// If we couldn't open the file we'll bail out
		if ( !file.good() )
			throw std::runtime_error("Failed to open file: " + filename);
		// Otherwise, create a string stream...
		std::stringstream stream;
		// ...and dump the contents of the file into it.
		stream << file.rdbuf();
		// Now that we've read the file we can close it
		// Finally, convert the stringstream into a string and return it
		return stream.str();
	// Private method to return the current shader program info log as a string
	std::string getInfoLog(ObjectType type, int id)
		GLint infoLogLength;
		if (type == ObjectType::SHADER)
			glGetShaderiv(id, GL_INFO_LOG_LENGTH, &infoLogLength);
		else // type must be ObjectType::PROGRAM
			glGetProgramiv(id, GL_INFO_LOG_LENGTH, &infoLogLength);
		GLchar *infoLog = new GLchar[infoLogLength + 1];
		if (type == ObjectType::SHADER)
			glGetShaderInfoLog(id, infoLogLength, NULL, infoLog);
		else // type must be ObjectType::PROGRAM
			glGetProgramInfoLog(id, infoLogLength, NULL, infoLog);
		// Convert the info log to a string
		std::string infoLogString(infoLog);
		// Delete the char array version of the log
		delete[] infoLog;
		// Finally, return the string version of the info log
		return infoLogString;
	// Constructor
		// We start in a non-initialised state - calling initFromFiles() or initFromStrings() will
		// initialise us.
		initialised = false;
		// Generate a unique Id / handle for the shader program
		// Note: We MUST have a valid rendering context before generating the programId or we'll segfault!
		programId = glCreateProgram();
		// Initially, we have zero shaders attached to the program
		shaderCount = 0;
	// Destructor
		// Delete the shader program from the graphics card memory to
		// free all the resources it's been using
	// Method to initialise a shader program from shaders provided as files
	void initFromFiles(std::string vertexShaderFilename, std::string fragmentShaderFilename)
		// Get the shader file contents as strings
		std::string vertexShaderSource   = loadShaderFromFile(vertexShaderFilename);
		std::string fragmentShaderSource = loadShaderFromFile(fragmentShaderFilename);
		initialise(vertexShaderSource, fragmentShaderSource);
	// Method to initialise a shader program from shaders provided as strings
	void initFromStrings(std::string vertexShaderSource, std::string fragmentShaderSource)
		initialise(vertexShaderSource, fragmentShaderSource);
	// Method to enable the shader program - we'll suggest this for inlining
	inline void use()
		// Santity check that we're initialised and ready to go...
		if (initialised)
			std::string msg = "Shader program " + programId;
			msg += " not initialised - aborting.";
			throw std::runtime_error(msg);
	// Method to disable the shader - we'll also suggest this for inlining
	inline void disable()
	// Method to return the bound location of a named attribute, or -1 if the attribute was not found
	GLuint attribute(const std::string attributeName)
		// You could do this method with the single line:
		//		return attributeMap[attribute];
		// BUT, if you did, and you asked it for a named attribute which didn't exist
		// like: attributeMap["FakeAttrib"] then the method would return an invalid
		// value which will likely cause the program to segfault. So we're making sure
		// the attribute asked for exists, and if it doesn't then we alert the user & bail.
		// Create an iterator to look through our attribute map (only create iterator on first run -
		// reuse it for all further calls).
		static std::map<std::string, int>::const_iterator attributeIter;
		// Try to find the named attribute
		attributeIter = attributeMap.find(attributeName);
		// Not found? Bail.
		if ( attributeIter == attributeMap.end() )
			throw std::runtime_error("Could not find attribute in shader program: " + attributeName);
		// Otherwise return the attribute location from the attribute map
		return attributeMap[attributeName];
	// Method to returns the bound location of a named uniform
	GLuint uniform(const std::string uniformName)
		// Note: You could do this method with the single line:
		// 		return uniformLocList[uniform];
		// But we're not doing that. Explanation in the attribute() method above.
		// Create an iterator to look through our uniform map (only create iterator on first run -
		// reuse it for all further calls).
		static std::map<std::string, int>::const_iterator uniformIter;
		// Try to find the named uniform
		uniformIter = uniformMap.find(uniformName);
		// Found it? Great - pass it back! Didn't find it? Alert user and halt.
		if ( uniformIter == uniformMap.end() )
			throw std::runtime_error("Could not find uniform in shader program: " + uniformName);
		// Otherwise return the attribute location from the uniform map
		return uniformMap[uniformName];
	// Method to add an attribute to the shader and return the bound location
	int addAttribute(const std::string attributeName)
		// Add the attribute location value for the attributeName key
		attributeMap[attributeName] = glGetAttribLocation( programId, attributeName.c_str() );
		// Check to ensure that the shader contains an attribute with this name
		if (attributeMap[attributeName] == -1)
			throw std::runtime_error("Could not add attribute: " + attributeName + " - location returned -1.");
		else // Valid attribute location? Inform user if we're in debug mode.
			if (DEBUG)
				std::cout << "Attribute " << attributeName << " bound to location: " << attributeMap[attributeName] << std::endl;
		// Return the attribute location
		return attributeMap[attributeName];
	// Method to add a uniform to the shader and return the bound location
	int addUniform(const std::string uniformName)
		// Add the uniform location value for the uniformName key
		uniformMap[uniformName] = glGetUniformLocation( programId, uniformName.c_str() );
		// Check to ensure that the shader contains a uniform with this name
		if (uniformMap[uniformName] == -1)
			throw std::runtime_error("Could not add uniform: " + uniformName + " - location returned -1.");
		else // Valid uniform location? Inform user if we're in debug mode.
			if (DEBUG)
				std::cout << "Uniform " << uniformName << " bound to location: " << uniformMap[uniformName] << std::endl;
		// Return the uniform location
		return uniformMap[uniformName];
}; // End of class

Note: I’m not convinced that the compiler will even consider inlining the use() and disable() methods when the program is built as a hpp – I think I’d have to break it into .h and .cpp files for that… other than that I’m thinking the above code is pretty clean, robust and usable.

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