OpenGL Console using SDL
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SDL Console

This is a console written using OpenGL for SDL. I needed a console for debugging and changing a running program and decided to roll my own.

SDL Console can handle window resizes, has an input history, and handles output from a user-defined input function.


SDL Console requires SDL2, OpenGL 2.1+, and Freetype. Debian-based distros can use the following command to get the required packages:

# apt-get install libfreetype6-dev libsdl2-dev

SDL Console was written for use in OpenGL-only applications. Mixing this library and SDL's draw calls, e.g. SDL_FillRect, is not advised but may work depending on the platform.

A monospace font is also required. I recommend SourceCode-Pro but any monospace font on your system will work.

How to Use

An example program can be seen at example.c. The example can be compiled with make example which can then be passed various fonts and sizes to test, e.g. ./example /path/to/font.ttf 18.

General flow

The library's contract should be short and sweet because that's what I needed. The basic flow of the contract is to 1) call Console_Create with the appropriate attributes, 2) call Console_Draw just before you flip buffers or render your frames, 3) call Console_Destroy to cleanup.

Here's some mock-code that illustrates this flow:

SDL_Window *window = program_init();
Console_tty *tty;
tty = Console_Create(
        window,         /* SDL_Window */
        18,             /* font size */
        SDLK_ESCAPE,    /* key that toggles console on/off */
        input_function, /* function that handles text input to console */
        NULL);          /* userdata to the above function */
if (!tty) {
    fprintf(stderr, "Console created failed: %s\n", Console_GetError());
    /* handle error */

while (program_is_on) {
    if (Console_Draw(tty)) {  /* handle drawing the console if toggled */
        fprintf(stderr, "%s\n", Console_GetError());
        /* handle fatal console error */

Console_Destroy(tty);   /* cleanup the console */

Input handling

The input function needs to be in the following form:

input_function (const char *input_text, void *userdata, char **output)
    if (strcmp(input_text, "foo") == 0)
        Console_SetOutput(output, "bar");
    return 0;

input_text is null-terminated text from the console, userdata' is userdata passed to Console_Createandoutput` is output from the function to be displayed on the console.

Please use Console_SetOutput to set the output. Console_SetOutput has two arguments: the first is output above and the second is a null-terminated string to be displayed on the console. If no output needs to occur, then simply do not set the output.

The input function should return 0 in almost all cases -- even common errors -- with the output set appropriately to be displayed in the console. In the case of a fatal error, still set the output normally but return 1. This error will be caught from Console_Draw in the main loop.


The default color for the font is white with no transparency and the default color for the background is black at 10% (0.9f) transparency. These can be changed via Console_SetFontColor and Console_SetBackgroundColor respectively. They both accept a Console_tty pointer as the first argument and then four floats -- r,g,b,a -- ranging from 0.0f to 1.0f.


SDL Console can be used statically apart of your project by just copying SDL_Console.h and SDL_Console.c to your project folder and linking against OpenGL, Freetype, and an appropriate math library. The Makefile shows an example on how to do this. Protip: Freetype is weird so just use freetype-config seen in the Makefile.

SDL Console can also be used as a shared library. Once you have the required packages simply enter make lib on your favorite console. Make sure your LD_LIBRARY_PATH (or your respective system's ld path) has's directory.