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Create Retna3D #631

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30 changes: 30 additions & 0 deletions Retna3D
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Original file line number Diff line number Diff line change
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// GLSL Fragment Shader Pseudocode

uniform sampler2D u_image; // The captured camera texture
varying vec2 v_texCoord; // Current texture coordinate (0.0 to 1.0)
Comment on lines +3 to +4
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@gemini-code-assist gemini-code-assist bot Nov 23, 2025

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critical

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)


void main() {
// Define the peripheral zone (bottom 50% of the image)
float peripheral_y_boundary = 0.5;

// Define the maximum shift amount (0.88 pixels converted to texture coordinate units)
float max_shift_coord = 0.88 / texture_width_pixels;

// 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) * 2.0;
float current_shift_x = max_shift_coord * ramp_factor;

// Apply the shift to the horizontal coordinate (x)
vec2 shifted_coord = vec2(v_texCoord.x + current_shift_x, v_texCoord.y);

// Fetch the color from the shifted coordinate
gl_FragColor = texture2D(u_image, shifted_coord);
} else {
// Top 50% (Clear Top) remains unshifted
gl_FragColor = texture2D(u_image, v_texCoord);
}
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@gemini-code-assist gemini-code-assist bot Nov 23, 2025

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high

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);

}