Question

I am in the process of learning OpenGL ES for Android from the following website:
http://www.learnopengles.com/android-lesson-one-getting-started/

Can someone please explain to me what shaders are. I looked around on the web, but the explanations are very confusing. What is a vertex shader compared to a fragment shader?

Thanks!

Answer 1

From Wikipedia:

Pixel shaders, also known as fragment shaders, compute color and other attributes of each pixel.

Pixel shaders range from always outputting the same color, to applying a lighting value, to doing bump mapping, shadows, specular highlights, translucency and other phenomena.

They can alter the depth of the pixel (for Z-buffering), or output more than one color if multiple render targets are active.

A pixel shader alone cannot produce very complex effects, because it operates only on a single pixel, without knowledge of a scene’s geometry.

Whereas:

Vertex shaders are run once for each vertex given to the graphics processor. The purpose is to transform each vertex’s 3D position in virtual space to the 2D coordinate at which it appears on the screen (as well as a depth value for the Z-buffer).

Vertex shaders can manipulate properties such as position, color, and texture coordinate, but cannot create new vertices.

The output of the vertex shader goes to the next stage in the pipeline, which is either a geometry shader if present or the rasterizer otherwise.

Essentially, pixel (fragment) shaders operate on what you see, a pixel. Vertex shaders operate on the vertex information present in the code. Vertex shaders are used earlier in the graphics pipeline.