Opengl 4 Error Handling
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Error will result. The errors are presented as an error code. For most OpenGL errors, and for most OpenGL functions, a function
Opengl Get Error String
that emits an error will have no effect. No OpenGL state will be opengl error 1282 changed, no rendering will be initiated. It will be as if the function had not been called. There are opengl error 1280 a few cases where this is not the case. This article is a stub. You can help the OpenGL Wiki by expanding it. Contents 1 Testing for errors 2 Meaning of
Opengl Error Codes
errors 3 Side effects Testing for errors OpenGL errors are stored in a queue until the error is actually handled. Therefore, if you do not regularly test for errors, you will not know necessarily which function call elicited a particular error. As such, error testing should be done regularly if you need to know where an error came from. To fetch the next
Glgeterror() Example
error in the queue (and to remove it from the queue), call this function: GLenum glGetError() If the error queue is empty, it will return GL_NO_ERROR. Otherwise, it will return one of the error enumerators below and remove that error from the queue. So to fetch all of the errors currently in the queue, you would need to loop: for(GLenum err; (err = glGetError()) != GL_NO_ERROR;) { //Process/log the error. } Meaning of errors The glGetError function returns one of the following error codes, or GL_NO_ERROR if no (more) errors are available. Each error code represents a category of user error. GL_INVALID_ENUM, 0x0500 Given when an enumeration parameter is not a legal enumeration for that function. This is given only for local problems; if the spec allows the enumeration in certain circumstances, where other parameters or state dictate those circumstances, then GL_INVALID_OPERATION is the result instead. GL_INVALID_VALUE, 0x0501 Given when a value parameter is not a legal value for that function. This is only given for local problems; if the spec allows the value in certain circumstances, where other parameters or state dictate those circumstances, then GL_INVALID_OPERATION is
OpenGL and GLSL: gDebugger. Although not totally compatible with version 3.3, it still provides a very good job alerting us to errors in our code, gluerrorstring allowing us to see the values of our uniforms, amongst many other features.
Opengl Error 1281
Anyway, back to our code. When we call a function from the OpenGL API we may be calling it incorrectly, opengl error minecraft and this is what glGetError is good for. "Incorrectly" can mean several things, for instance, the parameters are not in a valid range, or a function is being called without a proper context. https://www.opengl.org/wiki/OpenGL_Error OpenGL does not detect every possible error that may occur. This is due to performance reasons. Error tracking takes its toll on performance, and error free applications would be delayed unnecessarily. Every time an error is detected a flag is set and a numeric code is recorded. Any errors after that won't be recorded so we need to make sure we check for errors at the http://www.lighthouse3d.com/cg-topics/error-tracking-in-opengl/ most significant points in your application. To check if an error has occurred we use the function: GLenum glGetError(void); The return value can be one of the following: GL_INVALID_ENUM: a function has been called with an inappropriate enum. GL_INVALID_VALUE: A function has been called with a out of range numeric value. GL_INVALID_OPERATION: An operation has been performed out of context, or not allowed in the current state GL_INVALID_FRAMEBUFFER_OPERATION:vThe framebuffer object is not complete yet GL_OUT_OF_MEMORY: well, this one is pretty obvious… In all cases, except the last, the function produces no effect, i.e. the function is silently ignored. That is why it is so important to check for errors. In the last case, GL_OUT_OF_MEMORY, the outcome may be undefined. When an error is checked, the flag is cleared, and it will stay so until a new error occurs. Here are a few examples of errors: // causes a GL_INVALID_ENUM glEnable(GL_LINE); // causes a GL_INVALID_VALUE //when x >= GL_MAX_VERTEX_ATTRIBS glEnableVertexAttribArray(x); // causes a GL_INVALID_OPERATION // when n is negative or // is not a previously genererated index glBindBuffer(GL_ARRAY_BUFFER,n); And here is an example of a situation that although not correct, it will not cause an error: gl
or higher where the gluErrorString() is no longer available. Debugging with glGetError() Most people are used to work with a programming language that supports exceptions. This means that whenever you https://blog.nobel-joergensen.com/2013/01/29/debugging-opengl-using-glgeterror/ call a function with some illegal parameters, the function are capable of throwing http://www.glprogramming.com/red/chapter14.html a runtime exception telling the programmer what he did wrong. OpenGL is a C-based API, which means that there is no support for exceptions. Instead of exceptions OpenGL simply ignores the function call and set an exception flag. The programmer need to query the OpenGL error state when one or more OpenGL calls opengl error have been made - this is done using the glGetError function. Let's look at an example: void display() { glClearColor(1.,0.,0.,1.); glClear(GL_COLOR); // error - should be GL_COLOR_BUFFER_BIT // check OpenGL error GLenum err; while ((err = glGetError()) != GL_NO_ERROR) { cerr << "OpenGL error: " << err << endl; } glutSwapBuffers(); // Glut specific swap } The code above has an invalid use of glClear where the opengl 4 error parameter should be GL_COLOR_BUFFER_BIT instead of GL_COLOR. The result of running the program is a black screen and the error message "OpenGL error: 1281" is printed to the console. The error check must be in a loop since many errors can be have happened since last error check. It is certainly nice that the program now tells that an error occurred but what we really want is a more descriptive error message telling us the name of the OpenGL error enum instead of the value. It would also be nice having a single error check call instead of using a loop. Finally the error message should include where in your code the error occurred (in case your OpenGL program contains many error checks. To support these requirements I have create a small function and a macro which let you check for OpenGL errors using a single command. The code is also available as a Gist on GitHub [Link]. GLError.h #ifndef GLERROR_H #define GLERROR_H void _check_gl_error(const char *file, int line); /// /// Usage /// [... some opengl calls] /// glCheckError(); /// #define check_gl_error() _check_gl_error(__FILE__,__LINE__) #endif // GLERROR_H GLError.cpp #include "GLError.h" #include #ifdef WIN32 # include
you might find useful for your application. Some topics, such as error handling, don't fit into other categories, but are too short for an entire chapter. OpenGL is kind of a bag of low-level tools; now that you know about those tools, you can use them to implement higher-level functions. This chapter presents several examples of such higher-level capabilities. This chapter discusses a variety of techniques based on OpenGL commands that illustrate some of the not-so-obvious uses to which you can put these commands. The examples are in no particular order and aren't related to each other. The idea is to read the section headings and skip to the examples that you find interesting. For your convenience, the headings are listed and explained briefly here. Note: Most of the examples in the rest of this guide are complete and can be compiled and run as is. In this chapter, however, there are no complete programs, and you have to do a bit of work on your own to make them run.
"Error Handling" tells you how to check for OpenGL error conditions. "Which Version Am I Using?" describes how to find out details about the implementation, including the version number. This can be useful for writing applications that are backward compatible with earlier versions of OpenGL. "Extensions to the Standard" presents techniques to identify and use vendor-specific extensions to the OpenGL standard. "Cheesy Translucency" explains how to use polygon stippling to achieve translucency; this is particularly useful when you don't have blending hardware available. "An Easy Fade Effect" shows how to use polygon stippling to create the effect of a fade into the background. "Object Selection Using the Back Buffer" describes how to use the back buffer in a double-buffered system to handle simple object picking. "Cheap Image Transformation" discusses how to draw a distorted version of a bitmapped image by drawing each pixel as a quadrilateral. "Displaying Layers" explains how to display multiple different layers of materials and indicate where the materials overlap. "Antialiased Characters" describes how to draw smoother fonts. "Drawing Round Points" describes how to draw near-round points. "Interpolating Images" shows how to smoothly blend from one image to the another. "Making Decals" explains how to draw two images, where one is a sort of decal that should always appear on top of the other. "Drawing Filled, Concave