Fix half-pixel offsets in scaling renderer #231
Merged
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
- This bug was very subtle. It can be hard to notice! - Context: When the scaling renderer transformation matrix is created, it needs to center the image within the border. - The previous code always evaluated the translation to (0, 0) - This PR makes half-pixel adjustments to the translation when needed, making it impossible to rasterize the texture on a half-pixel boundary. - I spotted this while working on pixel-aspect-ratio support, but it can most easily be witnessed in the `conway` example by grabbing the top or bottom resize handle on the window and slow dragging it up and down by 1-pixel-at-a-time. When you hit a half-pixel bug the entire texture will change slightly; some pixels will become hidden.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
(0, 0)conwayexample by grabbing the top or bottom resize handle on the window and slow dragging it up and down by 1-pixel-at-a-time. When you hit a half-pixel bug the entire texture will change slightly; some pixels will become hidden or incorrectly duplicated.This bug is amazing! I can't believe I never noticed it, considering how seriously I take pixel-perfect rendering.
Here are some zoomed-in screenshots of before-and-after to highlight the bug. The object is intended to look more-or-less circular. This first image demonstrates a half-pixel offset on the vertical axis:
Before:
After:
And just in case you have trouble seeing it, here is an image that composes both together with the
afterversion blended using the difference operation at 95% opacity. This should make it very clear how the half-pixel offset hides and duplicates pixels.