Flat shading (animation)

Flat shading also called cel shading, or cel shading (also called toon shading) is a type of non-photorealistic rendering designed to make computer graphics appear hand-drawn. Flat shadows are commonly used to imitate the style of comics or cartoons. It is a relatively new addition to computer graphics, commonly seen in console video games. While the result of flat shading may appear as simplistic as hand-drawn animation, it is a complex process.

The name is due to the sheets of acetate (called cels in English, short for celluloid or celluloid), which are painted to be used in traditional 2D animations, such as Walt Disney's classics; shading is shading in English. The first time this technique was used was in the reboot ofDr. Slump(1997).

Process

The flat shading process begins with a typical 3D model. It differs from conventional rendering in its use of non-photorealistic lighting. Conventional (soft) lighting values are calculated for each pixel and then mapped to a small number of discrete shadows to create the characteristic flat look, in which shadows and highlights appear to be blocks of color rather than appearing mix gently.

The black ink exterior and outline lines can be created using a variety of methods. A popular method involves first rendering a black outline, somewhat larger than the object itself. Then it detects which parts are not visible from the selected point of view, and they are drawn in black. Shading can be done in several layers, to simulate more volume. After this, the non-visible areas are returned to a normal color to overlay the shading and apply the necessary textures. Finally, the image is sent to a z-axis buffer (to check depth), since shadows are placed deeper in scene rendering.

Below is an example of a teapot rendered using flat shading.

1. The rear faces are drawn with thin lines.
2. The object is drawn with a basic texture.
3. Hat.

Steps 2 and 3 can be combined using multitexturing (see texture mapping).

Another technique to achieve the exterior lines is to use 2D image processing. First, the scene is rendered (with flat shading) to a color texture the size of the screen:

Then the normal scene depth and world surface information is rendered to screen-sized textures:

A sobel filter or similar edge detection filter is applied to the normal and depth textures to generate an edge texture. The texels at the detected edges are black, while the other texels are white:

Finally, the border texture and the color texture are joined together to form the final rendered image:

Unlike most image processing techniques, the performance of this method is not affected by scene complexity.

History

The production of the demo

One of the first examples of a real-time shading cartoon is found in the Three Little Goats demo, made by Moppi (The Party, 1997).

Video games

The first video game that showed this technique was Worms 2 in its video sequences. But the first 3D game to offer real-time flat shading was Jet Set Radio (2000) for the Sega Dreamcast. A little earlier, at the end of 1999, Fear Effect was developed for PlayStation. While it was notable for its use of dramatic textures to give an anime-like appearance to its characters, it lacked outlines and a dynamic light source. Games before Fear Effect used textures in a similar way, but not as apparent or stylized as this game. Wacky Races, produced by Dreamcast a few months before Jet Set Radio, showed an outline effect that was wrong for cel-shading, this game actually used traditional shading techniques. There are other games, such as Mega Man Legends, that used static textures with high color contrast separation in the same pattern as Fear Effect, created before these examples, but the example created was not actually the flat shading, because they produced no outline effect and no shading.

In the following years after Jet Set Radio, numerous games with cel-shading technology were introduced during this "mini fad" that involved cel-shading graphics, however only few managed to match or surpass the established attractions. The next cel-shaded video games to capture the industry's attention in some way were Jet Set Radio Future, Sly Raccoon in 2002. Over time, more cel-shaded titles /i> such as XIII, Dark Chronicle, Cel Damage, Klonoa 2: Lunatea's Veil, Grand Theft Auto: Chinatown Wars, the Viewtiful Joe series, and XIII were produced with a positive, although they were not considered bestsellers according to their figures. Originally the only video games that received positive viewership and sales after Sly Cooper and the Thievius Raccoonus were The Legend of Zelda: The Wind Waker, The Legend of Zelda: Phantom Hourglass, The Legend of Zelda: Spirit Tracks, Sly 2: Band of Thieves, and Tales of Symphonia.

The House of the Dead III (HotD3) for the Xbox was initially designed as cel-shaded. Early in the development of the HotD3 Sega revealed photos of the then cel-shaded graphics to the gaming community. Shortly after those photos were revealed, Sega announced that they were abandoning cel-shaded graphics in favor of conventional graphics techniques. Several reasons are suspected for Sega's change of heart, the most popular being that its photos were met with a negative response from video gamers who did not like the style of cel shading graphics. Many players claimed that cel shading was just being used as a simple gimmick in an attempt to sell more games. HotD3 was a bloody and very violent low-weapons game that featured zombies and other mutated and deformed creatures. Many felt that the cel-shaded view did not match the themes and content of the game.

Another title worth highlighting is the outstanding Okami for PS2 and Wii, with very good results from critics and players, but not with much commercial success.

More recently, with consoles that were previously not powerful enough to render a fully 3D world, use has been made of cel-shading. Among the most notable video games are the Tony Hawk series, The Legend of Zelda: Phantom Hourglass and The Legend of Zelda: Spirit Tracks, as well as Grand Theft Auto: Chinatown Wars on the Nintendo DS.

Borderlands and Borderlands 2, in addition to the Crackdown saga, are some of the most relevant, where 3D graphics and cel shading are perfectly combined. It was released on the market in 2009 and has so far had 4 expansions.

In 2008 the reboot of Prince of Persia was released with "cel-shading" visualization; although commercially it was not very successful.

Both Marvel vs Capcom 3 and Ultimate Marvel vs. Capcom 3combines both 3D and "cel-shading" resembling a more comic-like appearance.

Currently Darksiders is the most surprising, and a very vivid and characteristic color scale, its sequel Darksiders II uses this technology again, and this time with a fascinating artistic section applauded by critics, it features the famous artist Joe Madureira, and is a reference in comic-style graphics.

In the video game saga, The Legend of Zelda, both The Legend of Zelda: Breath of the Wild, and its prequel Age of Calamity and its sequel, make use of graphics. >cel-shading.

Gallery

Two isosurfaces of the probabilistic density of a particle in a box, rendered following the shading cell method.