"Game engine light in light out" 4. shader

4. Shaders

「 The game engine   Shallow in, shallow out 」 Is an open source e-book ,PDF/ Code with the book / Download resources ： https://github.com/ThisisGame/cpp-game-engine-book

Shader is Shader,Shader It's just a paragraph GPU Program source code .

We learned it in College C Language is CPU Program source code ,Shader and C There are many similarities in language , Write code, too 、 compile 、 link .

Use the following table to make a comparison .

	C Language	Shader
Target hardware	CPU	GPU
Compilation process	Create project	establish GPU Program
	Create multiple code files	establish Shader object ( The vertices Shader And clips Shader)
	Write multiple codes	Upload Shader Source code to Shader object
	Compile code	compile Shader
	Add to link list	Add to link list
	link	link

Is it very similar ！

Render an image , In fact, in the GPU On the implementation of Shader Code , Then set the vertex coordinates 、 Color data as input , Through Shader To deal with , Then output pixel data to the screen .

and C The difference in language is ,C Language only needs one main.c The file can be compiled successfully .

however Shader It is a supporting , Vertex Shader( Vertex shader )、Fragment Shader( Fragment Shader ), You can't have one without the other .

	C Language	Shader
Target hardware	CPU	GPU
List of code files	main.c	main.vs(Vertex Shader)
	...	main.fs(Fragment Shader)

Types of shaders

Vertex Shader( Vertex shader )、Fragment Shader( Fragment Shader / Pixel shader ) These two are what we hear most .

Geometry Shader、Computer Shader Yes, but I haven't used it in actual projects .

Tessellation Control Shader 、Tessellation Evaluation Shader These two have hardly heard of .

This is determined by the work content , Everyone is engaged in mobile game development .

Mobile phones on the market at present , A large part is still OpenGL ES3.0 Version of or lower .

Computer Shader stay OpenGL ES 3.1 The version just started to support .

Geometry Shader stay OpenGL ES 3.2 The version just started to support .

 For more information, please refer to OpenGL Official website ：
https://www.khronos.org/opengl/wiki/Category:Shaders

This book only introduces Vertex Shader( Vertex shader )、Fragment Shader( Fragment Shader ).

stay 3. Drawing simple figures In the supporting projects in this chapter ,ShaderSource.h There is... In it Vertex Shader and Fragment Shader Source code .

Here's the picture ：

Look at this code , Also found and C Language similarities – All the entrances are main function .

	C Language	Shader
Target hardware	CPU	GPU
entrance	void main()	void main()

The current section is right Shader Just have a general image , The following chapters will introduce in detail .