Thumbnail position calculation

[paulJordaan]

Description

Fix Y position calculation for the getThumbnails funtion.
Fixes #3511

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to
  not work as expected)
• This change requires a documentation update

Checklist:

• I have signed the Google CLA https://cla.developers.google.com
• My code follows the style guidelines of this project
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have verified my change on multiple browsers on different platforms
• I have run ./build/all.py and the build passes
• I have run ./build/test.py and all tests pass

[avelad]

Should be: Math.floor(thumbnailPosition / rows) * height;

(columns vs rows)

[paulJordaan]

@avelad I've checked the logic again and the use of columns is correct. Consider the following as per the unit test.
Grid of 2x3 100x150px:

[0][1]
[2][3]
[4][5]

Requesting the position of thumbnail 5 using your suggested edit would result in the following:

Math.floor(thumbnailPosition / rows) * height
Math.floor( 5 / 3) * 50
1 * 50
yPosition = 50

The correct position for thumbnail 5 should be:

x= 50
y= 100

[shaka-bot]

All tests passed!