feat: add normal map preprocessing pipeline for correct channel layout conversion

[Limitex]

closes #40

[Copilot]

Pull request overview

This PR adds a normal-map-aware preprocessing and resize pipeline so normal maps can be resized/compressed without channel-layout corruption (DXTnm AG vs RG vs RGB) and without gamma/sRGB side effects.

Changes:

• Add NormalMapPreprocessor and NormalMapSourceLayoutDetector to detect/convert normal map channel layouts before compression.
• Update TextureCompressorService to preprocess normal maps before EditorUtility.CompressTexture, including fallback handling and semantic-alpha decisions for BC7.
• Update TextureProcessor to support isNormalMap resizing (linear read/write + higher-precision RT when available) and add extensive editor tests covering the pipeline end-to-end.

Reviewed changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
Editor/TextureCompressor/Core/Services/TextureProcessor.cs	Adds isNormalMap resize path using linear color space + float/half RT selection.
Editor/TextureCompressor/Core/Services/TextureCompressorService.cs	Integrates normal map preprocessing + source-layout detection into compression and fallback flow.
Editor/TextureCompressor/Core/Services/TextureFormatSelector.cs	Narrows responsibility to format prediction; exposes ResolvePlatform.
Editor/TextureCompressor/Core/Services/NormalMapPreprocessor.cs	New normal map channel packing/normalization logic for BC5/DXT5/BC7 + semantic alpha rules.
Editor/TextureCompressor/Core/Services/NormalMapSourceLayoutDetector.cs	New heuristic detector for AG vs RG vs RGB layouts in ambiguous formats (DXT5/BC7).
Tests/Editor/TestUtilities/NormalMapTestTextureFactory.cs (+ .meta)	Adds deterministic normal-map texture generators for test patterns and layouts.
Tests/Editor/Core/Services/TextureProcessorTests.cs	Expands resize tests to cover normal-map-specific behavior.
Tests/Editor/Core/Services/TextureFormatSelectorTests.cs	Removes compression-invocation tests now handled at service level; adds platform resolution tests.
Tests/Editor/Core/Services/TextureCompressorServiceTests.cs	Adds extensive integration tests for compression format selection, frozen overrides, layout detection, and alpha semantics.
Tests/Editor/Core/Services/NormalMapSourceLayoutDetectorTests.cs (+ .meta)	Adds unit tests for layout detection and resolve behavior.
Tests/Editor/Core/Services/NormalMapResizePipelineTests.cs (+ .meta)	Adds resize pipeline regression tests focused on normal map integrity.
Tests/Editor/Core/Services/NormalMapPreprocessorTests.cs (+ .meta)	Adds unit tests for preprocessing conversions and normalization behavior.
Tests/Editor/Core/Services/NormalMapPreprocessorPipelineTests.cs (+ .meta)	Adds end-to-end tests for resize + preprocess + real compression round-trips.
Tests/Editor/TestUtilities.meta	Adds Unity folder meta for new test utilities location.

Comments suppressed due to low confidence (1)

Editor/TextureCompressor/Core/Services/TextureProcessor.cs:177

• ResizeTo changes RenderTexture.active and allocates a temporary RenderTexture but doesn’t use a try/finally. If Graphics.Blit, ReadPixels, or Apply throws, RenderTexture.active may remain modified and the temporary RT may leak. Wrap the body in try/finally to always restore RenderTexture.active and ReleaseTemporary(rt) (and consider cleaning up the partially-created result).

                RenderTexture previous = RenderTexture.active;
                RenderTexture.active = rt;
                Graphics.Blit(source, rt);

                // Preserve mipmap setting from source texture
                // For normal maps, use linear color space to prevent gamma correction
                Texture2D result = new Texture2D(
                    newWidth,
                    newHeight,
                    TextureFormat.RGBA32,
                    source.mipmapCount > 1,
                    isNormalMap
                );
                result.ReadPixels(new Rect(0, 0, newWidth, newHeight), 0, 0);
                result.Apply(source.mipmapCount > 1);

                // Copy texture settings from source
                result.wrapModeU = source.wrapModeU;
                result.wrapModeV = source.wrapModeV;
                result.wrapModeW = source.wrapModeW;
                result.filterMode = source.filterMode;
                result.anisoLevel = source.anisoLevel;

                RenderTexture.active = previous;
                RenderTexture.ReleaseTemporary(rt);

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[Copilot]

Pull request overview

Copilot reviewed 21 out of 21 changed files in this pull request and generated 1 comment.

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