Update random rain

[ternaus]

Summary by Sourcery

Optimize the rain effect generation and update the tests.

Enhancements:

• Optimize add_rain using OpenCV polylines for faster rain generation.

Tests:

• Add tests to verify the shape, type, brightness, and visibility of rain drops, as well as to ensure the input image is preserved.

[sourcery-ai]

Reviewer's Guide by Sourcery

This pull request optimizes the add_rain function by using vectorized operations and improves the rain generation logic.

Sequence diagram for optimized rain effect generation

sequenceDiagram
    participant C as Client
    participant R as RainTransform
    participant F as add_rain Function
    participant CV as OpenCV

    C->>R: Apply rain transform
    R->>R: Generate rain parameters
    Note over R: Vectorized coordinate generation
    R->>F: Call add_rain with parameters
    F->>CV: Create rain layer
    F->>CV: Draw polylines (single call)
    F->>CV: Apply blur (if needed)
    F->>CV: Add rain layer to image
    F->>CV: Adjust brightness
    F-->>C: Return transformed image

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Flow diagram for optimized rain generation process

flowchart TD
    A[Start] --> B[Generate rain parameters]
    B --> C{Check num_drops}
    C -->|num_drops > 0| D[Generate coordinates vectorized]
    C -->|num_drops = 0| E[Create empty array]
    D --> F[Create rain layer]
    E --> F
    F --> G[Draw polylines]
    G --> H{Check blur value}
    H -->|blur > 1| I[Apply blur]
    H -->|blur <= 1| J[Skip blur]
    I --> K[Add rain layer to image]
    J --> K
    K --> L{Check brightness}
    L -->|coefficient != 1.0| M[Adjust brightness]
    L -->|coefficient = 1.0| N[Skip brightness]
    M --> O[End]
    N --> O

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File-Level Changes

Change	Details	Files
Optimized rain drop drawing using vectorized operations.	Replaced the loop for drawing rain drops with a single cv2.polylines call. Pre-allocated a rain layer to draw rain drops on. Removed the redundant blur operation. Used cv2.multiply for brightness adjustment instead of converting to HSV.	albumentations/augmentations/functional.py
Improved rain drop generation logic.	Simplified the calculation of the number of rain drops based on image height. Simplified the slant calculation. Generated all rain drop coordinates in a single call using random_generator.integers. Used a fixed proportion for drop length based on image height. Ensured that rain_drops is an empty array when num_drops is 0.	albumentations/augmentations/transforms.py
Added unit tests for the add_rain function.	Added tests to verify the shape and data type of the output image. Added tests to verify the brightness adjustment. Added tests to verify that rain drops are visible in the output. Added tests to verify that the input image is not modified.	tests/functional/test_functional.py

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[sourcery-ai]

Hey @ternaus - I've reviewed your changes and they look great!

Here's what I looked at during the review

• 🟡 General issues: 1 issue found
• 🟢 Security: all looks good
• 🟡 Testing: 1 issue found
• 🟢 Complexity: all looks good
• 🟢 Documentation: all looks good

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