Trap the water altitude via custom uniform

Trap Water Altitude/README.md

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+# Trap Water Altitude
+> by SpacEagle17
+
+This shader snippet provides a custom uniform to record the altitude of water bodies. The recorded altitude:
+
+- Defaults to 61.9 when exiting water, entering from a cave, or during shader reload
+- Maintains the entered altitude value until the player exits the water
+- Uses a smooth transition technique to capture the eye altitude while in water
+
+The code should be added to your `shaders.properties` file. Then, to use this functionality, declare the uniform in your shader program like this:
+```glsl
+uniform float waterAltitude = 61.9; // Tracks the altitude of water bodies, with default value for fallback
+```
+Works on Iris and OptiFine  
+Special thanks to Xonk for the large number smooth() trick used to record values.
+
+> Used in Euphoria Patches to progressively darken water as the player descends deeper
+
+For more information about custom uniforms, visit the [shaders.properties documentation](https://shaders.properties/current/reference/shadersproperties/custom_uniforms/).

Trap Water Altitude/trap-water-altitude.properties

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+# By SpacEagle17
+# Add the following code to your shaders.properties file.
+
+variable.float.trapWater = if(isEyeInWater == 1, 100000000000000.0, 0.0)
+variable.float.trapEyeAltitude = smooth(if(eyeBrightness.y < 224.0, 61.9, eyeAltitude - 1), trapWater, trapWater)
+uniform.float.waterAltitude = if(isEyeInWater != 1, 61.9, trapEyeAltitude)