Animating 2D Sprites in OpenGL

In working on my latest game, Praecursor, it came time to develop a system for easily animating sprites on the screen. I found a very nice sprite for a hero on OpenGameArt, and wanted to integrate his various animations into player actions. In the process, I created a CAnimation class that would extend the CRigidBody class, making it eligible to act just like a physical entity and be rendered on the screen with relative ease. The entire process was fairly challenging, requiring a custom file format parser and a new fragment shader. The following is a tutorial-like thought process that went into the development of animate-able sprites.

Layout

The CAnimation class is supposed to act exactly like a regular physical entity, but should support loading of custom .icanim files and have various functions related to animation. These include toggling animation, setting an automatic animation rate, quick-swapping sprite sheets, and manually switching sprites.

Quick-swapping seems like a pointless functionality of an animation class; after all, why not just create a separate instance and load it with the new sprite sheet? Well, I didn't think about this until I started trying to swap-out animations for running, jumping, and standing with the main player instance. When I would just have a list of animations and do m_Player = m_allAnimations[JUMP], the player would lose his physics properties, such as gravity or jump force. I tried a few workarounds, but none of them turned out like expected, so I decided to add a SwapSpriteSheet() method to the CAnimation class. This will attach a new texture to the material and give the shader new parameters based on width and heights.

In the future, I think I will change the class to incorporate animation boundaries, so I don't need to load a separate image for each animate-able action. I would be able to do something like SetAnimationIndex(0, JUMP), and the animation would only loop through sprites [0:JUMP], then if I wanted to just play the standing animation, I could do SetAnimationIndex(JUMP + 1, STAND), assuming the standing animation comes after the jumping one in the sprite sheet. This would likely all but eliminate the need for the swapping method.

Rendering Text in OpenGL Using FreeType Fonts

EDIT (04.14.2013): Tutorial updated to handle new-lines (\n character)

I finally decided to tackle the rendering of TrueType fonts in my engine. It proved to be a much bigger challenge than I had originally anticipated; I perused over dozens of outdated guides, tutorials, code snippets, and documentation files to finally achieve something legible on screen. I decided to provide a complete guide to this process so that if anyone should decide to follow in my footsteps, they will know where to go.

FreeType 2 Installation

OpenGL works with pixels, and TrueType fonts are not stored like image files, so we need the FreeType 2 library to create font bitmaps. If you are well-versed in 3rd party API installation, feel free to skip this section. I have only performed the compilation using Visual Studio 2010 and 2012.

• Download the latest headers for FreeType 2 from SourceForge. As of this write-up, the latest version is 2.4.11.
• Unzip the archive and go to the builds folder to locate your platform. I will be demonstrating this with the win32/vc2010 build.
• Open freetype.sln in Visual Studio. If you are running VS2012, you will need to update the solution to use the latest compiler and libraries.
• Select the Release candidate and go to Build->Build Solution.
• The compiled .lib file will be located in objs/win32/vc2010/freetype[version].lib, where [version] is "2411" as of this writing.
• Copy this file to somewhere in your current project directory's library path.
• Copy the contents of the include/ folder to somewhere in your current project directory's include path.