[my advanced OpenGL learning journey] about the access methods of vector and matrix classification of OpenGL shaders: xyzw/rgba/stpq and array subscripts

One 、 The expression of the individual components of a vector

The individual components of a vector can be accessed in two ways ：

1. Use “.” Operator .
2. Use The array subscript .

Two 、 Naming scheme

2.1 Three combined access methods

According to the number of components that make up the vector , Each component can be accessed through the following three combinations

1. {x,y,z,w}
   It usually represents a spatial coordinate (x,y,z,w), You can use... Separately .x、.y、.z and .w To get their first 1、2、3、4 Weight .
2. {r,g,b,a}
   Usually represents a color (r,g,b,a), You can use... Separately .r、.g、.b and .a To get their first 1、2、3、4 Weight .
3. {s,t,p,q}
   Usually represents a texture coordinate （s,t,p,q）, You can use... Separately .s、.t、.p and .q To get their first 1、2、3、4 Weight .

2.2 Meaning of combination mode

The reason for the three different naming schemes is that vectors can be used interchangeably to represent mathematical vector 、 Color and texture coordinates .

• x/r/s The component always refers to the... Of the vector 1 Weight .
• y/g/t The component always refers to the... Of the vector 2 Weight .
• z/b/p The component always refers to the... Of the vector 3 Weight .
• w/a/q The component always refers to the... Of the vector 4 Weight .
  Different naming conventions are just not convenient .

2.3 Precautions for combination mode

however , You cannot mix naming conventions when accessing vectors （ In other words , No .xgr Such reference methods , Because only one naming convention can be used at a time ）

3、 ... and 、 Use “.” Operator

Use "." Operator , You can rearrange the components of the vector in the operation .

Here is an example .

	vec3 myVec3 = vec3(0.0,1.0,2.0);   // myVec3 = {0.0,1.0,2.0}
	vec3 temp;
	
	temp = myVec3.xyz;                 // temp = {0.0,1.0,2.0}
	temp = myVec3.xxx;                 // temp = {0.0,0.0,0.0}
	temp = myVec3.zyx;                 // temp = {2.0,1.0,0.0}

Four 、 Use array subscripts "[]" Operator access

Besides using "." Operator , Use array subscripts "[]" Operator access .

In array subscript , Elements [0] Corresponding to x, Elements [1] Corresponding to y, wait .

A matrix is considered to consist of some vectors . for example ,mat2 It can be seen as two vec2,mat3 Can be seen as 3 individual vec3, wait .

For matrices , Individual columns can use the array subscript operator "[]" choice , Each vector can then be accessed through the vector access behavior .

Here are some examples of access matrices ：

 mat4 myMat4 = mat4(1.0);    // Initialize diagonal to 1.0 (identity)
    
 vex4 col0 = myMat4[0];      // Get col0 vector out of the matrix 
 float m1_1 = myMat4[1][1];  // Get element at [1][1] in matrix 
 float m2_2 = myMat4[2].z;    // Get element at [2][2] in matrix