The rise of God of War: Ascension
"One of the big takeaways [from God of War 3] was that the limits imposed by the engine (to ensure good performance) were restricting artist creativity, so we tried to remove or push those limits as far as possible without losing any performance. One example is the number of UV sets we allowed. We pushed it to three UV sets per mesh," Cedric Perthuis says, referring to a form of texture mapping used to wrap around specific shapes in the geometry. For complex character models such as Kratos, independent textures are needed for body parts unique to him, each wrapping around the head, torso and limbs - all of which form an editable "UV set" when laid out flat.
"[Ascension] also has more game systems competing for CPU and SPU time. A tremendous amount of time was spent 'under the hood', optimising systems and moving even more of the engine to the SPU."
God of War: Ascension incorporates significant enhancements to the Sony Santa Monica engine, specifically in terms of detailing, lighting and effects work.
Allowing multiple UV sets for the surrounding environment, however, also makes it possible to develop a far richer, more natural look to cracked mountain-sides and mossy cavern walls. According to Pethuis, this turns out to be a bit more expensive in terms of data size and vertex input bandwidth for the PS3 hardware, but the results are clearly worth it.
"With this we could now add layers of debris, dirt or grass and make those layers span smoothly across several geometries, while previously we had to add extra transparent meshes going across multiple other meshes, which wasn't always giving good results and could be fairly expensive too," he says.
"Pretty much every system saw its limits pushed," Perthuis adds, highlighting how other engine changes doubled or tripled the number of game objects the engine could handle. He also describes how the organic look of the environments has a basis in its more sophisticated "procedural mesh deformation for foliage and herbs, influenced by wind and collision."
However, even with such improvements in place, the sense of pushing back the frontiers on PS3 didn't feel as pronounced this time around as it was during the development of God of War 3 - something the team are ready to admit.
"From a graphics 'technical' perspective, to a large degree God of War: Ascension was more refinement on the graphics front," Diamand confirms, highlighting that his focus over the last three years has been "less in making whizz-bang graphics improvements, and instead doing a ton of optimisation work."
Even so, the changes beyond the back-end are still legion, with "shadows, many more models, more geometry, and significantly more use of multilayer shader features and effects" standing as the key areas of advancement.
"I thought we hit 11 in God of War, but Ascension belies that. Ascension also has more game systems competing for CPU and SPU time. A tremendous amount of time was spent under the hood, optimising systems and moving even more of the engine to the SPU."
"God of War: Ascension has more (and better) shadows, many more models, more geometry, and significantly more use of multi-layer shader features and effects."
These new game systems pertain to the game's lighting and animation - with the pay-off as far as playability goes being Kratos' new Life Cycle ability. With the Amulet of Uroboros to hand, giant structures can be healed or decayed to varying degrees, allowing our leading demi-god new platforming routes through stages, and a unique time-shifting dynamic for the many puzzles. However, the idea of terraforming the surroundings by manipulating time poses a particular challenge for designers when it comes to also reversing the game's many effects and its lighting.
"The material part was unusual but rather simple," Perthuis says, describing how lighting from the SPU could be "used to reveal or hide material layers or reveal or hide objects... we extended this to particles, lights, and every object. Then we added time to it which was a tremendous challenge. Getting our particle system to work both to advance time and go back in time was quite difficult. Synchronising the whole scene with lights, on and off states, baked physics destructions, light animations, and post-effects transitions was extremely time-consuming."
Due to the sunlight's directional lighting while outdoors, having structures - such as the lift mechanism at the start of Delos Island - shatter to pieces and reassemble relied on the shadows being dynamic, rather than baked into the environment. This turned out to be another trade-off in offering this mechanic. However, getting the technology in place to achieve real-time lighting on multiple flying pieces of debris did have a hand in encouraging the team to implement the Life Cycle mechanic in the first place.
"We had the idea to use special lights to do transitions between two layers of a given material. This would allow us to do transitions based on where the object was located in the world, without having to bake it and create a special instance of the geometry for that location. It was also more flexible and more lightweight than our traditional way of defining layer blending for materials. From there, we discovered that those lights could be dynamic, and suddenly it became something we could exploit for gameplay."
When it comes to particle effects in particular, Ascension stands as a vaulting leap over what was possible in God of War 3. Combat is on the centre stage for much of this prequel, with the friction sparks, licking flames and lightning strikes imbued in Kratos' weapon-based attacks showing this off vividly. Getting such combat effects to this level proved a vital area of exploration for the art team - but once again, this had its genesis in the engineering department first.
