It used to specifically be the part of a video game program that ran on the GPU to draw the shadows etc on the screen. It would compute things like the light intensity and angle and the geometry and placement of an object on screen and then decide where and how dark to draw the shadows for that object.
But now it basically refers to any sub program that runs on a GPU.
The picture you see is made of triangles. Each of those triangles has a texture on it, like a picture sticker. As the triangle rotates, the shape you see changes from a fat triangle to a thin sliver it you look at it almost edge on. A shader is a processor in a GPU that does the matrix algebra to figure out that apparent shape and them map the texture into the pixels you see on the screen.
**Shaders** are specialised computer programs that play a crucial role in rendering the graphics of video games (in a massively parallel way). They can also be used for general compute, although this is not always straightforward (think crypto currency for one common example).
More commonly, they are responsible for determining how light interacts with virtual surfaces, applying textures and colours, and creating various visual effects. In essence, Shaders act as the ‘digital artists and architects of the virtual world’, shaping the visual appearance of objects and environments. By manipulating the way light is reflected, refracted, and scattered, Shaders can create realistic and immersive visual experiences.
For instance, Shaders can be used to simulate the shimmering surface of water, the glossy sheen of metal, or the intricate details of a character’s clothing. Through the combination of different Shaders, game developers can achieve a wide range of visual styles and effects, from realistic to stylized.
Before the early 2000’s graphics hardware was mostly fixed function. It was not programmable. You gave the GPU drawing commands containing geometry, textures, texture coordinates, etc and it did the work of rendering them to the screen.
In the early 2000’s GPUs became more programmable. This is when we started to see more real-time lighting and shadows. The little programs are called shaders. Using shaders the programmer decides how things are rendered to the screen.
Imagine a window, it can alter light that passes through it, right?
For example, if it is blue, it will give a blue-ish tint, if its thicker in some places it may distort the image, and so on. It is something between your eyes and the world, that changes how you perceive it.
A shader is something like that: a “layer” that transforms, alter o distorts certain aspects of the image your GPU renders. Unlike a window, most shaders only alter a specific “part” or element in the image, for example, some shaders are for simulating realistic looking water, or shadows, or glass, even liquids, smoke, paint, metal, interiors, stars, visual effects, etc, etc, etc.
They are a powerful tool in the designers arsenal to create beatiful scenes, as they can be tweaked for multiple purposes: like creating the illusion of something that ain´t there, or add detail to an effect, shadow, texture or object.
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