Phoenix Engine

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Work in Progress: Comments & Edits Welcome

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* This page needs a list of graphical features in OG with links to blog posts and short descriptions of the features. If you have the time [SPF] has a thread with links to some articles.

The Phoenix Game Engine is the core technology behind Overgrowth, and is being developed specifically for the game. It includes a built-in level editor, with which users can make and modify game levels.

In order to achieve the desired fluidity in gameplay, the design principle behind the Phoenix engine emphasizes procedural generation of animation via keyframes and interpolation, and of sound effects through an ambient sound system.

In large part as a means of simplifying modifications, a scripting system utilizing AngelScript is deeply integrated into the game engine, which allows for control over various engine features.

Particle Effects

There isn't much information released about Overgrowth's particle system. Running or jumping on the ground creates small dust clouds at the characters' feet, and particle streams were added in A128 along with blood dripping. Particles are controlled through scripts, examples below:

Simple Particle Example

           MakeParticle("Data/Particles/impactfast.xml",pos,vec3(0.0f));

Particle Stream Example

           float blood_force = sin(time*_spurt_frequency)*0.5f+0.5f;
           uint32 id = MakeParticle("Data/Particles/blooddrop.xml",bleed_pos,(head_transform*vec3(0.0f,blood_amount*blood_force,0.0f)+this_mo.velocity));
           if(last_blood_particle_id != 0){
               ConnectParticles(last_blood_particle_id, id);
           }
           last_blood_particle_id = id;

Post Processing Effects

Post processing effects are image filters that are applied as a final step before each rendered frame is drawn to the screen -- much like Photoshop filters. This explanation is lifted word-for-word from David's blog post on the subject. He doesn't go into much detail about it in his blog posts, but here's links to part one and part two any way.

Shaders

Overgrowth uses GLSL shader language, and the users can create custom shaders. Some blog posts explain how some of the shaders work, such as the posts about Object Lightning, Character Rim Lighting and Trees in the Breeze. Overgrowth's character animation is also done through a shader, as David mentioned in a blog comment.

           The skeletal animation is done in the vertex shader anyway, so it's actually 
           faster and smoother-looking to just apply the bone matrices to the object-space 
           normal map than it is to recalculate transformed normals and tangents for 
           each vertex.
    

Motion Blur for Weapons

Overgrowth's weapons use motion blur based on stippling. Stippling is also used to render soft shadows, and the technique of stippling is explained in this old blog post. The motion blur for weapons works by drawing the weapon several times along it spath using different stipple patterns for each instance, as mentioned in the A135 video.

Relevant blog posts

A summary of most blog posts explaining Overgrowth's graphical features, focusing on more technical details. There are additional links below, some of which are not mentioned in the summary.

http://blog.wolfire.com/2008/12/object-lighting-part-1/ http://blog.wolfire.com/2010/02/Gamma-correct-lighting

http://blog.wolfire.com/2009/09/character-rim-lighting/ http://blog.wolfire.com/2009/10/character-normal-maps/ http://blog.wolfire.com/2009/09/soft-normal-maps-for-fur/

http://blog.wolfire.com/2009/09/trees-in-the-breeze/ http://blog.wolfire.com/2010/10/Imposters

http://blog.wolfire.com/2009/05/decals-editor-part-one/ http://blog.wolfire.com/2009/05/decals-editor-part-two/ http://blog.wolfire.com/2009/06/decals-editor-part-three/