Create Retna3D

[Thugga369]

Retania

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[gemini-code-assist]

Summary of Changes

Hello @Thugga369, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a new GLSL fragment shader, 'Retna3D', which is designed to apply a specific visual distortion to rendered images. The shader processes an input texture, applying a horizontal shift exclusively to the bottom half of the image. This shift gradually increases towards the bottom edge, creating a unique and dynamic visual effect.

Highlights

• New Shader File: A new GLSL fragment shader file named 'Retna3D' has been added to the repository.
• Visual Distortion Effect: The shader implements a unique visual distortion effect that horizontally shifts the bottom 50% of an input texture.
• Ramping Shift: The horizontal shift applied by the shader smoothly increases from zero at the image's mid-point (y=0.5) to a maximum value at the very bottom edge (y=1.0).

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[gemini-code-assist]

Code Review

This pull request introduces a GLSL fragment shader for a 'Retna3D' effect. My review focuses on ensuring the shader code is correct, robust, and maintainable. I've identified a critical compilation error due to an undeclared variable and have also suggested a refactoring to improve the main logic by removing code duplication, eliminating a magic number, and preventing potential rendering artifacts at the texture edges. Applying these suggestions will make the shader functional and more robust.

[gemini-code-assist]

The shader uses texture_width_pixels on line 11, but it's not declared as a uniform. This will cause a compilation error. You should declare it as a uniform to pass the texture's width from your application code.

uniform sampler2D u_image; // The captured camera texture
uniform float texture_width_pixels; // The width of the texture in pixels
varying vec2 v_texCoord;   // Current texture coordinate (0.0 to 1.0)

[gemini-code-assist]

This block of code can be refactored for better maintainability and robustness. Here are a few points:

• Code Duplication: The texture2D call is repeated in both the if and else branches. You can avoid this by using a variable for the texture coordinate and having a single texture2D call at the end.
• Magic Number: The value 2.0 on line 18 is a magic number. It's derived from peripheral_y_boundary being 0.5. Calculating it dynamically makes the code more robust if peripheral_y_boundary changes.
• Edge Artifacts: The shifted x-coordinate on line 22 can go beyond 1.0, which may cause texture wrapping artifacts. It's safer to clamp the coordinate to the [0.0, 1.0] range.

The suggested code below addresses these points.

    // By default, we sample from the original texture coordinate.
    vec2 sample_coord = v_texCoord;

    // Check if the current pixel is in the peripheral zone (bottom)
    if (v_texCoord.y > peripheral_y_boundary) {
        
        // Calculate a shift amount that smoothly ramps down to 0 at the boundary
        // and is maximum at the bottom edge (y=1.0)
        float ramp_factor = (v_texCoord.y - peripheral_y_boundary) / (1.0 - peripheral_y_boundary); 
        float current_shift_x = max_shift_coord * ramp_factor;

        // Apply the shift to the horizontal coordinate (x), clamping to avoid artifacts.
        sample_coord.x = clamp(v_texCoord.x + current_shift_x, 0.0, 1.0);
    }

    // Fetch the color from the (potentially shifted) coordinate.
    gl_FragColor = texture2D(u_image, sample_coord);