【帧内预测】8.4.4.2.2 Reference sample substitution process for intra sample prediction

Inputs to this process are: 
–  reference  samples  p[ x ][ y ]  with  x =  −1, y =  −1..nTbS * 2  − 1  and  x = 0..nTbS * 2  − 1,  y =  −1 for intra sample prediction, 
–  a transform block size nTbS, 
–  a variable cIdx specifying the colour  component of the current block. 
Outputs of this process are the modified  reference  samples  p[ x ][ y ]  with  x =  −1, y =  −1..nTbS * 2  − 1  and x = 0..nTbS * 2 − 1, y =  −1 for intra sample prediction. The variable bitDepth is derived as follows: 
–  If cIdx is equal to 0, bitDepth is set equal to BitDepthY （亮度）
–  Otherwise, bitDepth is set equal to BitDepthC （色差）
The values of the samples p[ x ][ y ] with x =  −1, y =  −1..nTbS * 2  − 1 and x = 0..nTbS * 2  − 1, y =  −1 are modified as follows: 
–  If  all  samples  p[ x ][ y ]  with  x =  −1, y =  −1..nTbS * 2  − 1  and  x = 0..nTbS * 2  − 1,  y = −1 are marked as "not available for intra prediction", the value 1  <<  ( bitDepth − 1 ) is substituted for the values of all samples p[ x ][ y ]. （若边界样点都无效，则边界用于帧内预测的参考样点值均设为 1  <<  ( bitDepth − 1 ) ）
–  Otherwise (at least one but not all samples p[ x ][ y ] ar e marked as "not available for intra prediction"), the following ordered steps are performed: （）

1.   When p[ −1 ][ nTbS * 2  − 1 ] is marked as "not available for intra prediction", search sequentially starting from x =  −1, y = nTbS * 2  − 1  to x =  −1, y =  −1, then from x = 0, y =  −1  to x = nTbS * 2 − 1,  y =  −1. Once a sample p[ x ][ y ] marked as "available for intra prediction" is found, the search is terminated and the value of p[ x ][ y ] is assigned to p[  −1 ][ nTbS * 2  − 1 ]. （第一个遍历点如果无效，则用遍历方向上的第一个有效点的值代替）
2.   Search sequentially starting from x = −1, y = nTbS * 2 − 2 to x =  −1, y =  −1, when p[ x ][ y ] is marked as "not available for intra prediction", the value of p[ x ][ y  + 1 ] is substituted for the value of p[ x ][ y ]. 
3.   For x = 0..nTbS * 2 − 1, y =  −1, when p[ x ][ y ] is marked as "not  available for intra prediction", the value of p[ x  − 1 ][ y ] is substituted for the value of p[ x ][ y ]. （2 和 3指的是无效点用遍历顺序的前一个有效点的值代替）
All  samples  p[ x ][ y ]  with  x = −1, y =  −1..nTbS * 2  − 1  and  x = 0..nTbS * 2  − 1,  y =  −1 are marked as "available for intra prediction"