What is the difference between opengl and GLSL?

Question

I recently started programming with openGL. I\'ve done code creating basic primitives and have used shaders in webGL. I\'ve googled the subject extensively but it\'s still not t

Answer 1

The short version is: OpenGL is an API for rendering graphics, while GLSL (which stands for GL shading language) is a language that gives programmers the ability to modify pipeline shaders. To put it another way, GLSL is a (small) part of the overall OpenGL framework.

To understand where GLSL fits into the big picture, consider a very simplified graphics pipeline.

Vertexes specified ---(vertex shader)---> transformed vertexes ---(primitive assembly)---> primitives ---(rasterization)---> fragments ---(fragment shader)---> output pixels

The shaders (here, just the vertex and fragment shaders) are programmable. You can do all sorts of things with them. You could just swap the red and green channels, or you could implement a bump mapping to make your surfaces appear much more detailed. Writing these shaders is an important part of graphics programming. Here's a link with some nice examples that should help you see what you can accomplish with custom shaders: http://docs.unity3d.com/Documentation/Components/SL-SurfaceShaderExamples.html.

In the not-too-distant past, the only way to program them was to use GPU assembler. In OpenGL's case, the language is known as ARB assembler. Because of the difficulty of this, the OpenGL folks gave us GLSL. GLSL is a higher-level language that can be compiled and run on graphics hardware. So to sum it all up, programmable shaders are an integral part of the OpenGL framework (or any modern graphics API), and GLSL makes it vastly easier to program them.