OpenGLAda – OpenGL binding for Ada

Overview

OpenGLAda is a thick OpenGL binding for the Ada 2005 programming language. Unlike other, thin, bindings (see the project's homepage for a list), OpenGLAda enriches the original API with concepts and features provided by Ada, like object orientation, type safety and generics.

Besides standard OpenGL functionality, OpenGLAda optionally provides bindings to the following OpenGL-related libraries:

• GLFW (opengl-glfw.gpr): This is a library for creating windows with an OpenGL context on them. It also provides functionality for capturing user input on keyboard, mouse and joystick. Having a window with an OpenGL context is the prerequisite for using any OpenGL functionality. The GLFW binding comes in two flavors: One for GLFW 2.x and one for GLFW 3+. There are significant differences between these two, the most prominent being that GLFW 3 can handle multiple windows. You can set the desired GLFW version for the binding at compile time.
• SOIL (opengl-soil.gpr): The Simple OpenGL Image Library. This is a very tiny library for loading image files into OpenGL textures. It is public domain. Because it's so tiny, it is linked directly into OpenGLAda. Its source is included in the OpenGLAda sources.
• FTGL (opengl-ftgl.gpr, deprecated): A library built on top of FreeType that provides an API to load TrueType fonts and render text with OpenGL. The Ada wrapper only provides basic functionality to load fonts and render text. As it does not include a wrapper to FreeType, the more low-level functionality has been excluded. This wrapper is not maintained anymore in favor of the new FreeType wrapper.
• FreeType (FreeTypeAda/freetype.gpr): A library for loading TrueType and OpenType fonts. OpenGLAda includes FreeTypeAda, a wrapper for the FreeType library. The project opengl-text.gpr provides an original higher-level API for rendering text based on FreeTypeAda.

OpenGLAda supports MacOSX, Windows and X11-based systems. API documentation can be found on the project's homepage.

Prerequisites

In order to build OpenGLAda, you need to have:

• A GNAT compiler¹. Compilers known to work well with OpenGLAda are GnuAda, AdaCore GNAT GPL 2017, and TDM-GCC. More information is available on the GCC website.
• GPRBuild (is bundled with AdaCore's GNAT distribution). TDM-GCC users can get it from here (NOTE: The gprbuild bundled in this zip is known not to work. For the time being, if you're using TDM-GCC, replace gprbuild with gnatmake in all commands even though that will tell you that project support in gnatmake is deprecated and will soon be removed. The reason for this incompatibility has not been found yet).
• An OpenGL implementation (usually comes bundled with your graphics driver)
• Optionally GLFW (OpenGLAda is pretty useless without the ability to create an OpenGL context.)
• Optionally FTGL (deprecated)
• Optionally FreeType

¹: You may also be able to build OpenGLAda with another Ada compiler and/or without using the *.gpr files. You just have to import the sources to your project and whichever build system you are using. I never used other Ada compilers apart from GNAT, so if I accidentally used some GNAT-specific features in the code, please drop me a message.

Installation

To install OpenGLAda with all optional libraries, execute

$ gprbuild [options] openglada.gpr
$ gprinstall [options] openglada.gpr

Where [options] is the set of scenario variables you want to use. The available variables are:

• Windowing_System: Sets the backend windowing system. Used for GLFW and also for system-dependent parts of the API (GLX, WGL, CGL):

  • x11: X Windowing System (Linux, BSD, etc)
  • windows: Microsoft Windows
  • quartz: Quartz Compositor (OS X)

• mode: May take one of the following values:

  • debug (default): Compile the project with debugging symbols and without optimization.
  • release: Compile the project for a release environment.

• Auto_Exceptions: Configures exception handling:

  • enabled (default): After each call to OpenGL, OpenGLAda checks whether OpenGL has set an error flag and if it had, raises the corresponding exception.
  • disabled: The user has to query the error flag on their own.

• GLFW_Version: Sets the version of the GLFW library to link against. See here for a detailed comparison of the two API versions.

  • 2: GLFW 2.x. Only one window.
  • 3 (default): GLFW 3+. Multiple windows, multiple monitor support, etc.

• GLFW_Linker_Param: Define how you will link to GLFW. Default is -lglfw everywhere but on Windows with GLFW 3, in which case it is -lglfw3.

• FreeType_Linker_Param: Define how you will link to FreeType. Default is -lfreetype.

For example, a typical Windows installation would be

$ gprbuild -XWindowing_System=windows -Xmode=release openglada.gpr
$ gprinstall -XWindowing_System=windows -Xmode=release openglada.gpr

Installing OpenGLAda makes its projects available to gprbuild and also to the GPS GUI. You can now import it like this:

with "opengl";
with "opengl-glfw";
with "opengl-text";
-- and so on

Note: The projects file openglada.gpr is just an aggregate project used for installation. In your projects, depend on opengl.gpr and its child projects.

If you are having trouble getting OpenGLAda to compile in your environment, please refer to the detailed guides on the website.

Tests

The tests in this repository are small programs that are mainly used to check if the basic system is working. You can build them with

$ make tests

If you're on Windows and do not have the make utility available, do this instead:

$ gprbuild -P opengl-glfw-test.gpr -XWindowing_System=windows
$ gprbuild -P opengl-test.gpr -XWindowing_System=windows

The tests require GLFW, because they need to create windows. By default, they try to link against GLFW 3+. You can instead build the tests against GLFW 2.x by executing:

$ gprbuild -P opengl-test.gpr -XWindowing_System=windows -XGLFW_Version=2
$ gprbuild -P opengl-glfw-test.gpr -XWindowing_System=windows -XGLFW_Version=2

(Substitute windows with x11 or quartz if needed.)

Examples

OpenGLAda comes bundled with a lot of examples. They have mostly been translated from C examples from OpenGL textbooks. They are located inside the examples folder. Each example has a separate .gpr file with which it can be built.

Contributions of examples are always welcome.

Developer Documentation

OpenGLAda autogenerates its API binding to OpenGL. The autogenerated source files are those in src/gl/generated and they are generated from the *.spec files in src/gl/specs. The syntax of the spec files is similar to Ada.

The reason behind this is that all functionality newer than OpenGL 1.1 is not expected to be provided by the OpenGL implementation. Instead, function pointers to the implementations should be queried at runtime. This makes it possible for the user to provide a fallback in case some OpenGL functionality is not available on the target system.

The generate tool compiled from src/generator will take care of creating both the API imports from OpenGL and the code for loading the function pointers at runtime. The tool is only necessary when adding OpenGL API functions to OpenGLAda and thus not of interest to the general user, since the autogenerated files are checked in to version control.

If you change the *.spec files, running make generate afterwards will update the autogenerated files. Be sure to check them in along with the spec changes.

License

OpenGLAda is distributed under the terms of the MIT License. The Ada 2012 logo that is used in the SOIL tests is distributed under the terms of the CC BY-ND 3.0 license, the original author is AdaCore.