Bottom and right boundary partition issue

[hangao]

Problem:
For bottom boundary ( y0 + cbHeight > pic_height_in_luma_samples, x0 + cbWidth <= pic_width_in_luma_samples) and cbSize is smaller then MinQTSizeY case:

allowSplitBtHor and allowSplitBtVer are both true, because of the the condition below in 6.4.1 is false:
-perpCbPos + perpCbSize is greater than perpMaxPicSize and cbSize is greater than MinQtSizeY

if both of allowSplitBtHor and allowSplitBtVer are true. mtt_split_cu_vertical_flag is present, which should not be present in this case. The same problem will happen in right boundary and cbSize is smaller then MinQTSizeY case.

Fix:
Reform the allowBtSplit conditions in 6.4.1 as follow to fix the problem and that make sure corner case is correct.

The variable allowBtSplit is derived as follows:
–If one or more of the following conditions are true, allowBtSplit is set equal to FALSE:

–cbSize is less than or equal to MinBtSizeY
–cbWidth is greater than MaxBtSizeY
–cbHeight is greater than MaxBtSizeY
–mttDepth is greater than or equal to MaxMttDepth + depthOffset
–perpCbPos + perpCbSize is greater than perpMaxPicSize and cbSize is greater than MinQtSizeY

–Otherwise if all of the following conditions are true, allowBtSplit is set equal to FALSE

–btSplit is equal to SPLIT_BT_VER
–x0 + cbWidth is greater than pic_width_in_luma_samples
–y0 + cbHeight is greater than pic_width_in_luma_samples

–Otherwise if all of the following conditions are true, allowBtSplit is set equal to FALSE:

–btSplit is equal to SPLIT_BT_VER
–y0 + cbHeight is greater than pic_height_in_luma_samples

–Otherwise if all of the following conditions are true, allowBtSplit is set equal to FALSE:

–btSplit is equal to SPLIT_BT_HOR
–x0 + cbWidth is greater than pic_width_in_luma_samples
–y0 + cbHeight is smaller than or equal to pic_height_in_luma_samples

–Otherwise if all of the following conditions are true, allowBtSplit is set equal to FALSE:

–mttDepth is greater than 0
–partIdx is equal to 1
–MttSplitMode[ x0 ][ y0 ][ mttDepth − 1 ] is equal to parallelTtSplit

–Otherwise, allowBtSplit is set equal to TRUE.

[bbross]

Fixed in VVC D2 v6