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…

Usage

// 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
shaderProgram->addAttribute("vertexLocation");
shaderProgram->addAttribute("vertexColour");
 
// Add uniforms to suit
shaderProgram->addUniform("mvpMatrix");
 
// 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>"
shaderProgram->use();
             glUniformMatrix4fv(shaderProgram->uniform("mvpMatrix"), 1, GL_FALSE, glm::value_ptr(mvpMatrix) );
             <YOUR-DRAW-CALL-HERE> i.e. glDrawArrays(GL_TRIANGLES, 0, 100) etc.
shaderProgram->disable();

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.
***/
 
#ifndef SHADER_PROGRAM_HPP
#define SHADER_PROGRAM_HPP
 
#include <iostream>
#include <fstream>
#include <sstream>
#include <map>
 
class ShaderProgram
{
private:
	// 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
	};
 
	// 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)
		{
			case GL_VERTEX_SHADER:
				shaderTypeString = "GL_VERTEX_SHADER";
				break;
			case GL_FRAGMENT_SHADER:
				shaderTypeString = "GL_FRAGMENT_SHADER";
				break;
			case GL_GEOMETRY_SHADER:
				throw std::runtime_error("Geometry shaders are unsupported at this time.");
				break;
			default:
				throw std::runtime_error("Bad shader type enum in compileShader.");
				break;
		}
 
		// 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
		glCompileShader(shaderId);
 
		// 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) );
		}
		else
		{
			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
		glLinkProgram(programId);
 
		// 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;
			}
		}
		else
		{
			throw std::runtime_error("Shader program link failed: " + getInfoLog(ObjectType::PROGRAM, programId) );
		}
 
		// Validate the shader program
		glValidateProgram(programId);
 
		// 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;
			}
		}
		else
		{
			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
		file.close();
 
		// 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;
	}
 
public:
	// Constructor
	ShaderProgram()
	{
		// 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();
		glUseProgram(programId);
 
		// Initially, we have zero shaders attached to the program
		shaderCount = 0;
	}
 
	// Destructor
	~ShaderProgram()
	{
		// Delete the shader program from the graphics card memory to
		// free all the resources it's been using
		glDeleteProgram(programId);
	}
 
	// 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)
		{
			glUseProgram(programId);
		}
		else
		{
			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()
	{
		glUseProgram(0);
	}
 
	// 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
 
#endif // SHADER_PROGRAM_HPP

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.

How To: Load an OpenGL Texture using the FreeImage library (or FreeImagePlus, technically)

I’d been using DevIL (or OpenIL if you prefer) as my image loader library, only it hasn’t been updated in a long time and can be a pain to build properly, so I’ve needed to move onto something else. The DevIL fork, ResIL, isn’t quite ready for prime-time and my attempts to build it have resulted in wasted hours and failure (I’ve fixed multiple build errors on the way – but then I hit stuff I can’t see how to fix without trying to re-package the entire thing).

So, new image library, huh? I had a google and saw the FreeImage library (and it’s FreeImagePlus version for C++ – documentation for which can be found here) – and it just happens to be in the Arch community repos so a quick sudo pacman -S freeimage later and we’re ready to rock… Only it didn’t come with any examples, so I dug around on forums and found some code that just about worked, but I wasn’t a big fan of it – so I thought I’d rewrite it into a nicer, more robust method – and I think I’ve achieved just that.

A textured quad at an angle.

The loadTexture Method

 
// Method to load an image into a texture using the freeimageplus library. Returns the texture ID or dies trying.
GLuint loadTexture(string filenameString, GLenum minificationFilter = GL_LINEAR, GLenum magnificationFilter = GL_LINEAR)
{
    // Get the filename as a pointer to a const char array to play nice with FreeImage
    const char* filename = filenameString.c_str();
 
    // Determine the format of the image.
    // Note: The second paramter ('size') is currently unused, and we should use 0 for it.
    FREE_IMAGE_FORMAT format = FreeImage_GetFileType(filename , 0);
 
    // Image not found? Abort! Without this section we get a 0 by 0 image with 0 bits-per-pixel but we don't abort, which
    // you might find preferable to dumping the user back to the desktop.
    if (format == -1)
    {
        cout << "Could not find image: " << filenameString << " - Aborting." << endl;
        exit(-1);
    }
 
    // Found image, but couldn't determine the file format? Try again...
    if (format == FIF_UNKNOWN)
    {
        cout << "Couldn't determine file format - attempting to get from file extension..." << endl;
 
        // ...by getting the filetype from the filename extension (i.e. .PNG, .GIF etc.)
        // Note: This is slower and more error-prone that getting it from the file itself,
        // also, we can't use the 'U' (unicode) variant of this method as that's Windows only.
        format = FreeImage_GetFIFFromFilename(filename);
 
        // Check that the plugin has reading capabilities for this format (if it's FIF_UNKNOWN,
        // for example, then it won't have) - if we can't read the file, then we bail out =(
        if ( !FreeImage_FIFSupportsReading(format) )
        {
            cout << "Detected image format cannot be read!" << endl;
            exit(-1);
        }
    }
 
    // If we're here we have a known image format, so load the image into a bitap
    FIBITMAP* bitmap = FreeImage_Load(format, filename);
 
    // How many bits-per-pixel is the source image?
    int bitsPerPixel =  FreeImage_GetBPP(bitmap);
 
    // Convert our image up to 32 bits (8 bits per channel, Red/Green/Blue/Alpha) -
    // but only if the image is not already 32 bits (i.e. 8 bits per channel).
    // Note: ConvertTo32Bits returns a CLONE of the image data - so if we
    // allocate this back to itself without using our bitmap32 intermediate
    // we will LEAK the original bitmap data, and valgrind will show things like this:
    //
    // LEAK SUMMARY:
    //  definitely lost: 24 bytes in 2 blocks
    //  indirectly lost: 1,024,874 bytes in 14 blocks    <--- Ouch.
    //
    // Using our intermediate and cleaning up the initial bitmap data we get:
    //
    // LEAK SUMMARY:
    //  definitely lost: 16 bytes in 1 blocks
    //  indirectly lost: 176 bytes in 4 blocks
    //
    // All above leaks (192 bytes) are caused by XGetDefault (in /usr/lib/libX11.so.6.3.0) - we have no control over this.
    //
    FIBITMAP* bitmap32;
    if (bitsPerPixel == 32)
    {
        cout << "Source image has " << bitsPerPixel << " bits per pixel. Skipping conversion." << endl;
        bitmap32 = bitmap;
    }
    else
    {
        cout << "Source image has " << bitsPerPixel << " bits per pixel. Converting to 32-bit colour." << endl;
        bitmap32 = FreeImage_ConvertTo32Bits(bitmap);
    }
 
    // Some basic image info - strip it out if you don't care
    int imageWidth  = FreeImage_GetWidth(bitmap32);
    int imageHeight = FreeImage_GetHeight(bitmap32);
    cout << "Image: " << filenameString << " is size: " << imageWidth << "x" << imageHeight << "." << endl;
 
    // Get a pointer to the texture data as an array of unsigned bytes.
    // Note: At this point bitmap32 ALWAYS holds a 32-bit colour version of our image - so we get our data from that.
    // Also, we don't need to delete or delete[] this textureData because it's not on the heap (so attempting to do
    // so will cause a crash) - just let it go out of scope and the memory will be returned to the stack.
    GLubyte* textureData = FreeImage_GetBits(bitmap32);
 
    // Generate a texture ID and bind to it
    GLuint tempTextureID;
    glGenTextures(1, &tempTextureID);
    glBindTexture(GL_TEXTURE_2D, tempTextureID);
 
    // Construct the texture.
    // Note: The 'Data format' is the format of the image data as provided by the image library. FreeImage decodes images into
    // BGR/BGRA format, but we want to work with it in the more common RGBA format, so we specify the 'Internal format' as such.
    glTexImage2D(GL_TEXTURE_2D,    // Type of texture
                 0,                // Mipmap level (0 being the top level i.e. full size)
                 GL_RGBA,          // Internal format
                 imageWidth,       // Width of the texture
                 imageHeight,      // Height of the texture,
                 0,                // Border in pixels
                 GL_BGRA,          // Data format
                 GL_UNSIGNED_BYTE, // Type of texture data
                 textureData);     // The image data to use for this texture
 
    // Specify our minification and magnification filters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, minificationFilter);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, magnificationFilter);
 
    // If we're using MipMaps, then we'll generate them here.
    // Note: The glGenerateMipmap call requires OpenGL 3.0 as a minimum.
    if (minificationFilter == GL_LINEAR_MIPMAP_LINEAR   ||
        minificationFilter == GL_LINEAR_MIPMAP_NEAREST  ||
        minificationFilter == GL_NEAREST_MIPMAP_LINEAR  ||
        minificationFilter == GL_NEAREST_MIPMAP_NEAREST)
    {
        glGenerateMipmap(GL_TEXTURE_2D);
    }
 
    // Check for OpenGL texture creation errors
    GLenum glError = glGetError();
    if(glError)
    {
        cout << "There was an error loading the texture: "<< filenameString << endl;
 
        switch (glError)
        {
            case GL_INVALID_ENUM:
                cout << "Invalid enum." << endl;
                break;
 
            case GL_INVALID_VALUE:
                cout << "Invalid value." << endl;
                break;
 
            case GL_INVALID_OPERATION:
                cout << "Invalid operation." << endl;
 
            default:
                cout << "Unrecognised GLenum." << endl;
                break;
        }
 
        cout << "See https://www.opengl.org/sdk/docs/man/html/glTexImage2D.xhtml for further details." << endl;
    }
 
    // Unload the 32-bit colour bitmap
    FreeImage_Unload(bitmap32);
 
    // If we had to do a conversion to 32-bit colour, then unload the original
    // non-32-bit-colour version of the image data too. Otherwise, bitmap32 and
    // bitmap point at the same data, and that data's already been free'd, so
    // don't attempt to free it again! (or we'll crash).
    if (bitsPerPixel != 32)
    {
        FreeImage_Unload(bitmap);
    }
 
    // Finally, return the texture ID
    return tempTextureID;
}

Usage

To use the method, just set up your code something like this – in your main .cpp file at the top have:

#include <iostream>
#include <cstdlib>
 
// OpenGL/GLEW/GLFW/SDL/Whatever headers
 
// Include the FreeImagePlus library (don't forget to link your project to the .so/.a or to the lib/dll on Windows)
#include <FreeImagePlus.h>
 
using std::string;
using std::cout;
using std::endl;
 
// Create a handle for our texture
GLuint textureID;

In your initialisation/setup method add something like this:

//  ----- Initialise the FreeImage library -----
// Note: Flag is whether we should load ONLY local (built-in) libraries, so
// false means 'no, use external libraries also', and 'true' means - use built
// in libs only, so it's like using the library as a static version of itself.
FreeImage_Initialise(true);

In your main method, once you’ve create an OpenGL context (i.e. window) and called your initialise/setup method, then you can load a texture to use like this:

// Load an image and bind it to a texture
textureID = loadTexture("TestImage.png");
 
// Or load an image using trilinear filtering via mipmaps for minification and GL_LINEAR (the method's default) for magnification
textureID = loadTexture("TestImage.png", GL_LINEAR_MIPMAP_LINEAR);
 
// Or load an image using low quality mipmaps for minification and GL_NEAREST for magnification.
// The point is that you can set the minification and magnification parameters separately, not necessarily that you'd choose these interpolation options.
textureID = loadTexture("TestImage.png", GL_NEAREST_MIPMAP_NEAREST, GL_NEAREST);

Finally, on shutdown you may (optionally, as long as you’re not using the Linux/Mac .a version of the library) like to add the following:

// As we're using a .so version of the freeimageplus library on Linux we
// don't need to call DeInitialise (we would only really HAVE to do so on Linux
// or Mac [not Windows!] when using the .a version) - but it doesn't hurt to do it anyway.
FreeImage_DeInitialise();

Wrap-up

Not a great deal to say – it works, it should be relatively robust, it doesn’t leak memory (or at least none that we control), and the code is commented to the hilt and explains why it’s doing things instead of just what it’s doing (some people don’t like verbose code like this – but I teach a lot of programming so I just try to explain everything as clearly as possible as I go – and find I prefer it to ‘terse’ code that I have no idea WTF it’s up to or why it’s bothering).

Many thanks to the FreeImage devs for the library – it’s rather feature-packed and I quite like it (some good example code wouldn’t go amiss though!) =D

Hope you find the code useful! (Bugs? Comments? Suggestions? Feedback always welcome!).

A Simple C++ OpenGL Shader Loader

Update: There’s a re-worked and improved version of this shader loading code here: https://r3dux.org/2015/01/a-simple-c-opengl-shader-loader-improved/ – you should probably use that instead of this.


I’ve been doing a bunch of OpenGL programming recently and wanted to create my own shader classes to make setting up shaders as easy as possible – so I did ;-) To create vertex and fragment shaders and tie them into a shader program you can just import the Shader.hpp and ShaderProgram.hpp classes and use code like the following:

// Set up vertex shader
Shader vertexShader(GL_VERTEX_SHADER);
vertexShader.loadFromFile("MyVertexShader.vert");
vertexShader.compile();
 
// Set up fragment shader
Shader fragmentShader(GL_FRAGMENT_SHADER);
fragmentShader.loadFromFile("MyFragmentShader.frag");
fragmentShader.compile();
 
// Set up shader program
shaderProgram = new ShaderProgram();
shaderProgram->attachShader(vertexShader);
shaderProgram->attachShader(fragmentShader);
shaderProgram->linkProgram();

There’s also a loadFromString(some-string-containing-GLSL-source-code) method, if that’s your preference.

The ShaderProgram class uses a string/int map as a key/value pair, so to add attributes or uniforms you just specify their name and they’ll have a location assigned to them:

// Add the shader attributes
shaderProgram->addAttribute("vVertex");
// ...
 
// Add the shader uniforms
shaderProgram->addUniform("pMatrix");
// ...

The ShaderProgram class then uses two methods called attribute and uniform to return the bound locations (you could argue that I should have called these methods getAttribute and getUniform – but I felt that just attribute and uniform were cleaner in use. Feel free to mod if you feel strongly about it). When binding vertex attribute pointers you can use code like this:

// Set up a vertex buffer object to hold the vertex position data
GLuint vertexBufferId;
glGenBuffers(1, &vertexBufferId);
glBindBuffer(GL_ARRAY_BUFFER, vertexBufferId);
glBufferData(GL_ARRAY_BUFFER, model.getVertexDataSizeBytes(), model.getVertexData(), GL_STATIC_DRAW);
 
// Set up the vertex attribute pointer for the vVertex attribute
glVertexAttribPointer(
    shaderProgram->attribute("vVertex"),  // Attribute location
    VERTEX_COMPONENTS,                    // Number of elements per vertex, here (x,y,z), so 3
    GL_FLOAT,                             // Data type of each element
    GL_FALSE,                             // Normalised?
    0,                                    // Stride
    0                                     // Offset
);

Finally, when drawing your geometry you can get just enable the shader program, provide the location and data for bound uniforms, and then disable it like this (I’m using the GL Mathematics library for matrices – you can use anything you fancy):

shaderProgram->use();
 
    // Provide uniform data
    glUniformMatrix4fv( shaderProgram->uniform("mMatrix"), 1, GL_FALSE, glm::value_ptr(mMatrix) );
    // ...
 
    // Draw stuff
 
shaderProgram->disable();

That’s pretty much it – nice and simple. I haven’t done anything with geometry shaders yet so I’ve no idea if there’s anything else you’ll need, but if so it likely won’t be too tricky a job to implement it yourself. Anyways, you can look at the source code for the classes themselves below, and I’ll put the two classes in a zip file here: ShaderHelperClasses.zip.

As a final note, you can’t create anything shader-y without having a valid OpenGL rendering context (i.e. a window to draw stuff to) or the code will segfault – that’s just how it works. The easiest way around this if you want to keep a global ShaderProgram object around is to create it as a pointer (i.e. ShaderProgram *shaderProgram;) and then initialise it later on when you’ve got the window open with shaderProgram = new ShaderProgram(); like I’ve done above.

Cheers! =D

Source code after the jump…