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Bug 4188 - Software renderer SDL_RenderCopyEx blits corrupt image under certain cases
Summary: Software renderer SDL_RenderCopyEx blits corrupt image under certain cases
Status: RESOLVED FIXED
Alias: None
Product: SDL
Classification: Unclassified
Component: render (show other bugs)
Version: 2.0.8
Hardware: x86_64 All
: P2 normal
Assignee: Sam Lantinga
QA Contact: Sam Lantinga
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2018-06-07 01:30 UTC by duckgrease
Modified: 2018-10-30 14:00 UTC (History)
2 users (show)

See Also:

Attachments
corrupt SDL_RenderCopyEx example code (3.29 KB, text/plain)
2018-06-07 01:30 UTC, duckgrease 		Details
patch (2.95 KB, patch)
2018-10-09 09:46 UTC, Sylvain 		Details | Diff
patch v2 (4.28 KB, patch)
2018-10-17 19:32 UTC, Sylvain 		Details | Diff
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Description duckgrease 2018-06-07 01:30:11 UTC 
Created attachment 3255 [details]
corrupt SDL_RenderCopyEx example code

SDL_RenderCopyEx blits wrong image (in some cases it's bunch of alternating horizontal lines, some cases it's image from the wrong coordinate, and in some cases it's just a bunch of garbled pixels), when the following conditions are met:
- Use software renderer.
- Enable either horizontal or vertical flip.
- source and destination rectangles must have same width and height, and must be smaller than the size of the texture.
- source rectangle's X and Y coordinates must be 0.

I was able to reproduce this problem on both Windows 10 and Linux 64 bit, from version 2.0.3 to latest 2.0.8.

Attached an example (modified from the 2D software rendering example code). Go to line 62 and disable flip and you'll see non-corrupt image.
Comment 1 Sylvain 2018-10-09 09:46:12 UTC 
Created attachment 3355 [details]
patch

You're right. This has never worked perfectly. 
Last commit was almost fine https://hg.libsdl.org/SDL/rev/1e1ce9f6d215 bug #3029

This patch fixes rotations 0/90/180/270 with/out flip (0, Vertical,Horizontal,Both).
Comment 2 Sam Lantinga 2018-10-10 00:41:58 UTC 
Patch added, thanks!
https://hg.libsdl.org/SDL/rev/b19b09eb9e6d
Comment 3 Sylvain 2018-10-17 19:32:12 UTC 
Created attachment 3381 [details]
patch v2

Re-opening this issue.

It fixes the test-case, but it introduces a regression with another bug (bug #4313).

So here's a new patch that activate cropping of the source surface to solve the issue.
It also reverts the wrong changeset.
It prevents unneeded colorkey error message.
Comment 4 Sylvain 2018-10-17 20:15:29 UTC 
marked as reopened
Comment 5 Ozkan Sezer 2018-10-30 12:07:28 UTC 
Sam:  Do we need this for 2.0.9 ?
Comment 6 Sylvain 2018-10-30 12:40:19 UTC 
Oops, I forgot to activate you. Yep you really want this. It fixes my regression and the bug.
Comment 7 Sam Lantinga 2018-10-30 14:00:26 UTC 
Patch added, thanks!
https://hg.libsdl.org/SDL/rev/bced4041fcc0