78:T1bfc, ## Description At full color range with 4:2:0, the CUDA NV12 kernel (`RGBA_to_NV12` in `src/platform/linux/cuda.cu`) writes incorrect chroma for pure red and pure blue. Moonlight then shows `#ff0000` as green and `#0000ff` as dark green. This code runs on Linux with an NVIDIA GPU. The cause is an unclamped store. The kernel scales chroma by 256 and stores the float in a `uint8_t`. For `#ff0000`, V is 128/255 \+ 0.5, approximately 1.002. Scaled, this gives 256.5, and the store wraps it to 0. Blue has the same problem with U. `#fe0000` and `#0000fe` give approximately 256.0, so the rounding of the float calculation decides if they wrap. The 4:4:4 kernel scales by 255, has a maximum of 255.5 and cannot wrap. I did not change it. Changes: - `src/platform/linux/cuda_color.h` is a new header. Its two functions compile for the GPU and for the host: - `clamp_to_uint8()` clamps a sample to the range 0 to 255. NaN gives 0. - `nv12_chroma_sample()` calculates the average of a 2x2 block in the same order as the old kernel code. Then it clamps the result. - `RGBA_to_NV12` uses `nv12_chroma_sample()`. The arithmetic is the same as before, except for the clamp. - `cuda::test::convert_to_nv12()` is a test hook in `cuda.cu` and `cuda.h`. It runs the real NV12 kernel on a frame from host memory. Only builds with `SUNSHINE_TESTS` include it. I put the clamp in a header so that unit tests can check it on a host without a GPU. ### Screenshot Before before-fix

After

### Issues Fixed or Closed - Fixes \#5953 #### Roadmap Issues ## Testing I added `tests/unit/platform/linux/test_cuda_color.cpp`. It has two test suites: - `CudaColorTest` (5 tests) runs on all hosts. It checks these items: - The clamp at the edges, at ±infinity and at NaN. - Full\-range V of `#ff0000` and U of `#0000ff` stay at 255 for Rec. 601, Rec. 709 and Rec. 2020. - 11 colors in all six 8\-bit colorspaces agree with the ITU\-T H.273 formula, within 1 code value. - Limited\-range chroma stays between 16 and 240. - The chroma of a block is the average of its four pixels. - `CudaNv12KernelTest` (2 tests) runs the real kernel through the test hook on solid frames. It checks the chroma plane against the same formula. It also checks that full\-range red and blue keep the maximum value. The tests skip if there is no CUDA device, as on CI. Checks that I ran: - I built `CudaColorTest` with GoogleTest and Apple clang (C\+\+23) on macOS. I used a copy of `color_vectors_from_colorspace()` from `src/video_colorspace.cpp`. All 5 tests pass. - Regression check: I put the old unclamped store back into `nv12_chroma_sample()`. Then `FullRangePureRedAndBlueKeepMaximumChroma` and `Nv12ChromaMatchesTheColorspaceMatrix` fail, with V of red and U of blue at 0. - `CudaNv12KernelTest` compiles against `src/platform/linux/cuda.h` (clang `-fsyntax-only`). - `clang-format` with the repository configuration makes no changes to the changed files. - Manual test: I ran Sunshine with this change on the same host and client as in \#5953 (Moonlight for macOS, HEVC 8\-bit, 4:2:0, full range). I used the six\-color test card from the issue. Before the fix, `#ff0000` shows as green and `#0000ff` shows as dark green. With the fix, all six colors show correctly. I added screenshots from before and after the fix. ## Type of Change - [ ] **feat**: New feature (non\-breaking change which adds functionality) - [x] **fix**: Bug fix (non\-breaking change which fixes an issue) - [ ] **docs**: Documentation only changes - [ ] **style**: Changes that do not affect the meaning of the code (white\-space, formatting, missing semicolons, etc.) - [ ] **refactor**: Code change that neither fixes a bug nor adds a feature - [ ] **perf**: Code change that improves performance - [ ] **test**: Adding missing tests or correcting existing tests - [ ] **build**: Changes that affect the build system or external dependencies - [ ] **ci**: Changes to CI configuration files and scripts - [ ] **chore**: Other changes that don't modify src or test files - [ ] **revert**: Reverts a previous commit - [ ] **BREAKING CHANGE**: Introduces a breaking change (can be combined with any type above) ## Checklist - [x] Code follows the style guidelines of this project - [x] Code has been self\-reviewed - [x] Code has been commented, particularly in hard\-to\-understand areas - [x] Code docstring/documentation\-blocks for new or existing methods/components have been added or updated - [x] Tests have been added or updated for new or modified functionality, including regression tests for bug fixes ### AI Usage See our [AI usage policy](https://docs.lizardbyte.dev/latest/developers/contributing.html#ai-usage). - [x] AI tools were used while preparing this PR I used an AI agent. It found the cause in `cuda.cu`, wrote the fix and the tests, ran the checks above, and wrote a draft of this description. I found the bug, reproduced it with a test card, and tested the workarounds in \#5953. 79:Tc09,## [![Quality Gate Passed](https://cdn.trylle.com/media/images/9c421b538b25f3b09f4b2fe2b0372ec2?key=AcQi5aACo4g%2FYo5l5IjHF3xVl6%2FNs4GJqvnQmK1WYQSdtSdRF26f%2FHvQaxVtYfwO5Zmn8dluvsUfc7rMx%2B%2FgQY2OVykvJejXvd9AGYYByqXGzgFAz8gNAGxDHrnoHKtqik9jZGG8QAdOiWU9mFubBHZXaF9DzWU0BmQyy0MI3IUIg8dPDcYRSwg1fpo1NafBvh5XrY6twS%2B7azc0BlfnOuF%2F1fUWs5kIgW%2Fyqnll0eMqf1%2BqbdHuUxive7nB4cFYbX1HRO8%3D "Quality Gate Passed")](https://sonarcloud.io/dashboard?id=LizardByte_Sunshine&pullRequest=5962) **Quality Gate passed** Issues\ ![](https://cdn.trylle.com/media/images/1f80bcb90d79b2b11bb739f48a001eba?key=AUC4JpfjThVa%2Bs177EUoO7i8HgbzCRl8Z01fv0xPDZPLrH%2BDQmUptp2xqyXz6Ry5UVz15ge3hfUJfcrNsco49HOerENB6eluOhBp2S6N6eD%2BR8aS31oqgsuMjumS%2FmD8yI8EO6a6pU6kCSlBJSXMdzHQdpi2f29zd6J3eWkDgK27I67k4Q%2FGj8yrJg24QPoLAitYTBYgMAOhTN%2FUCC%2FmZ0m0c0v6pN10QUhZhOgt%2BmAQ "") [0 New issues](https://sonarcloud.io/project/issues?id=LizardByte_Sunshine&pullRequest=5962&issueStatuses=OPEN,CONFIRMED&sinceLeakPeriod=true)\ ![](https://cdn.trylle.com/media/images/2dc6921822f23cc8f5227994feb4f3a1?key=Ac0A%2B0GOiKtG7s6yUOkdAw93Omn2d6UW4CeD2L0U%2BJBRKNXLhiTbhcAYui4CWhVpOt5sS%2FIpI5GuMUAr%2BR7rVdKH%2BhxG6gKozNa21fwbQxSdpTU%2FjZ2iFl9kDiolBU4S%2BRFIeFGghV92lOKfCd6%2BYiGPTNPcoNmsgSbkTS3%2FbidmrAdQOrK9LWMRC%2FNHb3Q89TG%2B6T73DUYy9yDpnhpnR17g1F78itSkkEQd60W2pU9pWj4%3D "") [0 Accepted issues](https://sonarcloud.io/project/issues?id=LizardByte_Sunshine&pullRequest=5962&issueStatuses=ACCEPTED) Measures\ ![](https://cdn.trylle.com/media/images/1f80bcb90d79b2b11bb739f48a001eba?key=AUC4JpfjThVa%2Bs177EUoO7i8HgbzCRl8Z01fv0xPDZPLrH%2BDQmUptp2xqyXz6Ry5UVz15ge3hfUJfcrNsco49HOerENB6eluOhBp2S6N6eD%2BR8aS31oqgsuMjumS%2FmD8yI8EO6a6pU6kCSlBJSXMdzHQdpi2f29zd6J3eWkDgK27I67k4Q%2FGj8yrJg24QPoLAitYTBYgMAOhTN%2FUCC%2FmZ0m0c0v6pN10QUhZhOgt%2BmAQ "") [0 Security Hotspots](https://sonarcloud.io/project/security_hotspots?id=LizardByte_Sunshine&pullRequest=5962&issueStatuses=OPEN,CONFIRMED&sinceLeakPeriod=true)\ ![](https://cdn.trylle.com/media/images/1f80bcb90d79b2b11bb739f48a001eba?key=AUC4JpfjThVa%2Bs177EUoO7i8HgbzCRl8Z01fv0xPDZPLrH%2BDQmUptp2xqyXz6Ry5UVz15ge3hfUJfcrNsco49HOerENB6eluOhBp2S6N6eD%2BR8aS31oqgsuMjumS%2FmD8yI8EO6a6pU6kCSlBJSXMdzHQdpi2f29zd6J3eWkDgK27I67k4Q%2FGj8yrJg24QPoLAitYTBYgMAOhTN%2FUCC%2FmZ0m0c0v6pN10QUhZhOgt%2BmAQ "") [0.0% Coverage on New Code](https://sonarcloud.io/component_measures?id=LizardByte_Sunshine&pullRequest=5962&metric=new_coverage&view=list)\ ![](https://cdn.trylle.com/media/images/1f80bcb90d79b2b11bb739f48a001eba?key=AUC4JpfjThVa%2Bs177EUoO7i8HgbzCRl8Z01fv0xPDZPLrH%2BDQmUptp2xqyXz6Ry5UVz15ge3hfUJfcrNsco49HOerENB6eluOhBp2S6N6eD%2BR8aS31oqgsuMjumS%2FmD8yI8EO6a6pU6kCSlBJSXMdzHQdpi2f29zd6J3eWkDgK27I67k4Q%2FGj8yrJg24QPoLAitYTBYgMAOhTN%2FUCC%2FmZ0m0c0v6pN10QUhZhOgt%2BmAQ "") [0.0% Duplication on New Code](https://sonarcloud.io/component_measures?id=LizardByte_Sunshine&pullRequest=5962&metric=new_duplicated_lines_density&view=list) [See analysis details on SonarQube Cloud](https://sonarcloud.io/dashboard?id=LizardByte_Sunshine&pullRequest=5962) 7a:T4b8,fix(linux/cuda): clamp NV12 chroma so full-range red and blue do not wrap RGBA_to_NV12 scales chroma by 256 and stores the float into a uint8_t without a clamp. At full range, V of pure red and U of pure blue are 128/255 + 0.5, about 1.002, so the scaled value is 256.5 and wraps to 0. Moonlight clients that request full-range 4:2:0 then show #ff0000 as green and #0000ff as dark green. Move the chroma store into src/platform/linux/cuda_color.h, a header whose helpers compile for both the GPU and the host: - clamp_to_uint8() clamps a sample to [0, 255]. - nv12_chroma_sample() averages a 2x2 block in the same order as the old kernel code, then clamps. The NV12 kernel calls nv12_chroma_sample(). The 4:4:4 kernel scales by 255, peaks at 255.5 and cannot wrap, so it is unchanged. Tests in tests/unit/platform/linux/test_cuda_color.cpp: - CudaColorTest runs on any host. It checks the clamp, the colors from the issue, every 8-bit colorspace against the ITU-T H.273 formula, and the limited-range bounds. - CudaNv12KernelTest runs the real kernel through a test-only hook, cuda::test::convert_to_nv12() (SUNSHINE_TESTS builds only), and skips when no CUDA device is present. 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Commits on Tue, Oct 20, 2026