Remove unused code in Perlin noise 1D impl (#19765)

# Objective

- Fix #19759 
- The bigger permutation table only comes into play for higher
dimensions than 1, when you start doing
`PERMUTATION_TABLE[PERMUTATION_TABLE[index] + some_number]`
- The bigger permutation table has no mathematical meaning, it's just
there to avoid having to write more `& 0xFF` when doing multiple nested
lookups in higher dimensions
- But we only use 1D Perlin noise for the camera shake because we want
the dimensions to be uncorrelated

## Solution

- So, we can trim the permutation table down :) 
- This should be mathematically identical, as a wrapped value will still
access the same element as an unwrapped value would in the bigger table
- The comment was a bit misleading anyways. "mirror" did not refer to
"mirrored values" but to "repeated values".

## Testing

- Ran the example. Still behaves like before.

examples/camera/2d_screen_shake.rs

@@ -226,21 +226,22 @@ mod perlin_noise {
 
     pub fn generate(x: f32) -> f32 {
         // Left coordinate of the unit-line that contains the input.
-        let xi0 = x.floor() as usize;
+        let x_floor = x.floor() as usize;
 
         // Input location in the unit-line.
-        let xf0 = x - xi0 as f32;
+        let xf0 = x - x_floor as f32;
         let xf1 = xf0 - 1.0;
 
         // Wrap to range 0-255.
-        let xi = xi0 & 0xFF;
+        let xi0 = x_floor & 0xFF;
+        let xi1 = (x_floor + 1) & 0xFF;
 
         // Apply the fade function to the location.
         let t = fade(xf0).clamp(0.0, 1.0);
 
         // Generate hash values for each point of the unit-line.
-        let h0 = PERMUTATION_TABLE[xi];
+        let h0 = PERMUTATION_TABLE[xi0];
-        let h1 = PERMUTATION_TABLE[xi + 1];
+        let h1 = PERMUTATION_TABLE[xi1];
 
         // Linearly interpolate between dot products of each gradient with its distance to the input location.
         let a = dot_grad(h0, xf0);
@@ -263,8 +264,8 @@ mod perlin_noise {
         }
     }
 
-    // Perlin noise permutation table, the second half is a mirror of the first half.
+    // Perlin noise permutation table. This is a random sequence of the numbers 0-255.
-    const PERMUTATION_TABLE: [u8; 512] = [
+    const PERMUTATION_TABLE: [u8; 256] = [
         0x97, 0xA0, 0x89, 0x5B, 0x5A, 0x0F, 0x83, 0x0D, 0xC9, 0x5F, 0x60, 0x35, 0xC2, 0xE9, 0x07,
         0xE1, 0x8C, 0x24, 0x67, 0x1E, 0x45, 0x8E, 0x08, 0x63, 0x25, 0xF0, 0x15, 0x0A, 0x17, 0xBE,
         0x06, 0x94, 0xF7, 0x78, 0xEA, 0x4B, 0x00, 0x1A, 0xC5, 0x3E, 0x5E, 0xFC, 0xDB, 0xCB, 0x75,
@@ -282,23 +283,6 @@ mod perlin_noise {
         0x91, 0xEB, 0xF9, 0x0E, 0xEF, 0x6B, 0x31, 0xC0, 0xD6, 0x1F, 0xB5, 0xC7, 0x6A, 0x9D, 0xB8,
         0x54, 0xCC, 0xB0, 0x73, 0x79, 0x32, 0x2D, 0x7F, 0x04, 0x96, 0xFE, 0x8A, 0xEC, 0xCD, 0x5D,
         0xDE, 0x72, 0x43, 0x1D, 0x18, 0x48, 0xF3, 0x8D, 0x80, 0xC3, 0x4E, 0x42, 0xD7, 0x3D, 0x9C,
-        0xB4, 0x97, 0xA0, 0x89, 0x5B, 0x5A, 0x0F, 0x83, 0x0D, 0xC9, 0x5F, 0x60, 0x35, 0xC2, 0xE9,
+        0xB4,
-        0x07, 0xE1, 0x8C, 0x24, 0x67, 0x1E, 0x45, 0x8E, 0x08, 0x63, 0x25, 0xF0, 0x15, 0x0A, 0x17,
-        0xBE, 0x06, 0x94, 0xF7, 0x78, 0xEA, 0x4B, 0x00, 0x1A, 0xC5, 0x3E, 0x5E, 0xFC, 0xDB, 0xCB,
-        0x75, 0x23, 0x0B, 0x20, 0x39, 0xB1, 0x21, 0x58, 0xED, 0x95, 0x38, 0x57, 0xAE, 0x14, 0x7D,
-        0x88, 0xAB, 0xA8, 0x44, 0xAF, 0x4A, 0xA5, 0x47, 0x86, 0x8B, 0x30, 0x1B, 0xA6, 0x4D, 0x92,
-        0x9E, 0xE7, 0x53, 0x6F, 0xE5, 0x7A, 0x3C, 0xD3, 0x85, 0xE6, 0xDC, 0x69, 0x5C, 0x29, 0x37,
-        0x2E, 0xF5, 0x28, 0xF4, 0x66, 0x8F, 0x36, 0x41, 0x19, 0x3F, 0xA1, 0x01, 0xD8, 0x50, 0x49,
-        0xD1, 0x4C, 0x84, 0xBB, 0xD0, 0x59, 0x12, 0xA9, 0xC8, 0xC4, 0x87, 0x82, 0x74, 0xBC, 0x9F,
-        0x56, 0xA4, 0x64, 0x6D, 0xC6, 0xAD, 0xBA, 0x03, 0x40, 0x34, 0xD9, 0xE2, 0xFA, 0x7C, 0x7B,
-        0x05, 0xCA, 0x26, 0x93, 0x76, 0x7E, 0xFF, 0x52, 0x55, 0xD4, 0xCF, 0xCE, 0x3B, 0xE3, 0x2F,
-        0x10, 0x3A, 0x11, 0xB6, 0xBD, 0x1C, 0x2A, 0xDF, 0xB7, 0xAA, 0xD5, 0x77, 0xF8, 0x98, 0x02,
-        0x2C, 0x9A, 0xA3, 0x46, 0xDD, 0x99, 0x65, 0x9B, 0xA7, 0x2B, 0xAC, 0x09, 0x81, 0x16, 0x27,
-        0xFD, 0x13, 0x62, 0x6C, 0x6E, 0x4F, 0x71, 0xE0, 0xE8, 0xB2, 0xB9, 0x70, 0x68, 0xDA, 0xF6,
-        0x61, 0xE4, 0xFB, 0x22, 0xF2, 0xC1, 0xEE, 0xD2, 0x90, 0x0C, 0xBF, 0xB3, 0xA2, 0xF1, 0x51,
-        0x33, 0x91, 0xEB, 0xF9, 0x0E, 0xEF, 0x6B, 0x31, 0xC0, 0xD6, 0x1F, 0xB5, 0xC7, 0x6A, 0x9D,
-        0xB8, 0x54, 0xCC, 0xB0, 0x73, 0x79, 0x32, 0x2D, 0x7F, 0x04, 0x96, 0xFE, 0x8A, 0xEC, 0xCD,
-        0x5D, 0xDE, 0x72, 0x43, 0x1D, 0x18, 0x48, 0xF3, 0x8D, 0x80, 0xC3, 0x4E, 0x42, 0xD7, 0x3D,
-        0x9C, 0xB4,
     ];
 }