Linux shell programming

 - without permission change

/bin/sh <name of script>

- make scrhipt to be an excutable file

chmod +x <name of script>

sar : system activity report

on linux

sar : system activity report

Rendering : Glossary

• OpenGL: a formal specification of a graphics API that defines the layout and output of each function.

• GLAD: an extension loading library that loads and sets all OpenGL’s function pointers for us so we can use all (modern) OpenGL’s functions.

• Viewport: the 2D window region where we render to.

• Graphics Pipeline: the entire process vertices have to walk through before ending up

as one or more pixels on the screen.

• Shader: a small program that runs on the graphics card. Several stages of the graphics

pipeline can use user-made shaders to replace existing functionality.

• Vertex: a collection of data that represent a single point.

• Normalized Device Coordinates: the coordinate system your vertices end up in

after perspective division is performed on clip coordinates. All vertex positions in NDC

between -1.0 and 1.0 will not be discarded or clipped and end up visible.

• Vertex Buffer Object: a buffer object that allocates memory on the GPU and stores

all the vertex data there for the graphics card to use.

• Vertex Array Object: stores buffer and vertex attribute state information.

• Element Buffer Object: a buffer object that stores indices on the GPU for indexed

drawing.

• Uniform: a special type of GLSL variable that is global (each shader in a shader program

can access this uniform variable) and only has to be set once.

• Texture: a special type of image used in shaders and usually wrapped around objects,

giving the illusion an object is extremely detailed.

• Texture Wrapping: defines the mode that specifies how OpenGL should sample textures

when texture coordinates are outside the range: (0, 1).

• Texture Filtering: defines the mode that specifies how OpenGL should sample the

texture when there are several texels (texture pixels) to choose from. This usually occurs

when a texture is magnified.

• Mipmaps: stored smaller versions of a texture where the appropriate sized version is chosen based on the distance to the viewer.

• stb_image: image loading library.

• Texture Units: allows for multiple textures on a single shader program by binding

multiple textures, each to a different texture unit.

• Vector: a mathematical entity that defines directions and/or positions in any dimension.

• Matrix: a rectangular array of mathematical expressions with useful transformation properties.

• GLM: a mathematics library tailored for OpenGL.

• Local Space: the space an object begins in. All coordinates relative to an object’s origin.

• World Space: all coordinates relative to a global origin.

• View Space: all coordinates as viewed from a camera’s perspective.

• Clip Space: all coordinates as viewed from the camera’s perspective but with projection

applied. This is the space the vertex coordinates should end up in, as output of the vertex

108 Chapter 11. Review shader. OpenGL does the rest (clipping/perspective division).

• Screen Space: all coordinates as viewed from the screen. Coordinates range from 0 to

screen width/height.

• LookAt: a special type of view matrix that creates a coordinate system where all coordinates are rotated and translated in such a way that the user is looking at a given target from a given position.

• Euler Angles: defined as yaw, pitch and roll that allow us to form any 3D direction

vector from these 3 values.

V, I, R

Current - C / s, A

Voltage - J / C, V

R - (J * s) / C^2, Ohm  or V / A

ex) If I have 10V and 2mA then I can calculate R which is 5k Ohm

Predicting the future is hard so try improve something iteratively.

Predicting the future tends to be a waste of time and resources. It is better to take a breadth-first approach and get the basics right. Then, let the details emerge and plan on regular refactoring to keep the architecture healthy.

RTM

 Requirements/Reverse Traceability Matrix

요구 사항이 실제 설계, 테스트케이스, 코드로 어떻게 구현되었는지 역추적 할 수 있다.

Performance Optimization -Riot tech blog-

I'm really enjoying read these articles. especially optimizations.

https://technology.riotgames.com/news/profiling-case-missing-milliseconds

interesting thing is that just put one equal sign op removes 2ms stall.

currentTimeInMs > startTime + timeout 

replace to

currentTimeInMs >= startTime + timeout

In addition, Riot tech blog has tons of great articles there so you should check that out.