Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Change definition of scanline in text. #117

Open
wants to merge 1 commit into
base: master
Choose a base branch
from
Open

Change definition of scanline in text. #117

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
2 changes: 1 addition & 1 deletion content/video.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@ Whereas sound and joypad functionality have to make do with only a few measly re

## Draw and blank periods {#sec-blanks}

As said, the entire GBA screen is refreshed every 60th of a second, but there's more to it than that. After a scanline has been drawn (the HDraw period, 240 pixels), there is a pause (HBlank, 68 pixels) before it starts drawing the next scanline. Likewise, after the 160 scanlines (VDraw) is a 68 scanline blank (VBlank) before it starts over again. To avoid tearing, positional data is usually updated at the VBlank. This is why most games run at 60 or 30 fps. (FYI, syncing at the VBlank is also why we in PAL countries often had slower games: PAL TVs run (ran) at 50Hz, hence only 50 fps instead of 60, hence a 17% slower game if nobody bothered to account for it. Few companies ever did <kbd>:(</kbd> ).
As said, the entire GBA screen is refreshed every 60th of a second, but there's more to it than that. After all the pixels in one line has been drawn (the HDraw period, 240 pixels), there is a pause (HBlank, 68 pixels) before it starts drawing the next line. The combination of these two is called scanline. Likewise, after the 160 scanlines (VDraw) is a 68 scanline blank (VBlank) before it starts over again. To avoid tearing, positional data is usually updated at the VBlank. This is why most games run at 60 or 30 fps. (FYI, syncing at the VBlank is also why we in PAL countries often had slower games: PAL TVs run (ran) at 50Hz, hence only 50 fps instead of 60, hence a 17% slower game if nobody bothered to account for it. Few companies ever did <kbd>:(</kbd> ).

Both the [CowBite Spec](http://www.cs.rit.edu/~tjh8300/CowBite/CowBiteSpec.htm#Graphics%20Hardware%20Overview) and [GBATEK](https://problemkaputt.de/gbatek.htm#lcddimensionsandtimings) give you some interesting details about the timings of the display. A full screen refresh takes exactly 280896 cycles, divided by the clock speed gives a framerate of 59.73. From the Draw/Blank periods given above you can see that there are 4 cycles per pixel, and 1232 cycles per scanline. You can find a summary of timing details in table 4.1.

Expand Down