[Feat/Fix] Easing snapshots (#4)

* create snapshots folder, but ignore its contents

* script to generate snapshots of easing plots

* fix all broken easings

* update readme

.gitignore

@@ -7,3 +7,4 @@ phpunit.xml
 phpstan.neon
 testbench.yaml
 vendor
+tests/Snapshots/*.png

README.md

@@ -59,6 +59,20 @@ $x = (new Tween())
 composer test
 ```
 
+### Visual Snapshot Testing
+To generate plots of all `Ease` methods, from the project root, run
+```bash
+./scripts/generateSnapshots
+```
+The 256x256 PNGs will be generated in the `tests/Snapshots` directory.
+These snapshots will be ignored by git, but allow visual inspection of the plots to
+compare against known good sources, like [Easings.net](https://easings.net).
+
+> **Note** The `scripts` directory _may_ need to have its permissions changed to allow script execution
+```bash
+chmod -R 777 ./scripts
+```
+
 ## Changelog
 
 Please see [CHANGELOG](CHANGELOG.md) for more information on what has changed recently.

scripts/generateSnapshots

@@ -0,0 +1,36 @@
+#!/usr/bin/env php
+<?php
+
+require_once __DIR__.'/../vendor/autoload.php';
+
+use ProjektGopher\FFMpegTween\Enums\Ease as AvailableEasings;
+use ProjektGopher\FFMpegTween\Ease;
+
+echo 'starting... (fail fast)'.PHP_EOL;
+
+$time = "X/H";
+
+foreach (AvailableEasings::cases() as $ease) {
+    echo "Generating snapshot for {$ease->value} easing...".PHP_EOL;
+    $easeMultiplier = Ease::{$ease->value}($time);
+
+    $input = "-f lavfi -i \"color=c=black:s=256x256:d=1\"";
+    $margin = '28';
+    $filter = "-vf \"geq=if(eq(round((H-2*{$margin})*({$easeMultiplier}))\,H-Y-{$margin})\,128\,0):128:128\"";
+    $out = "-frames:v 1 -update 1 tests/Snapshots/{$ease->value}.png";
+    $redirect = '2>&1'; // redirect stderr to stdout
+
+    $cmd = "ffmpeg -y {$input} {$filter} {$out} {$redirect}";
+
+    (array) $output = [];
+    (int) $code = 0;
+    exec($cmd, $output, $code);
+
+    if ($code !== 0) {
+        echo PHP_EOL;
+        echo "Failed to generate snapshot for {$ease->value} easing.".PHP_EOL;
+        echo "Output: ".PHP_EOL;
+        echo implode(PHP_EOL, $output).PHP_EOL;
+        exit(1);
+    }
+}

src/Ease.php

@@ -111,7 +111,8 @@ public static function EaseInOutExpo(string $time): string
         $firstExp = "pow(2\\,20*({$time})-10)/2";
         $secondExp = "(2-pow(2\\,-20*({$time})+10))/2";
 
-        return "if(eq(({$time})\\,0)\\,0\\,(if(eq(({$time})\\,1)\\,1\\,if(lt(({$time})\\,0.5)\\,pow(2\\,20*({$firstExp})-10)/2)\\,(2-pow(2\\,-20*({$secondExp})+10))/2)))";
+        // We have to set the return value for 0 and 1 explicitly as we lose accuracy at the 4th decimal place.
+        return "if(eq(({$time})\\,0)\\,0\\,if(eq(({$time})\\,1)\\,1\\,if(lt(({$time})\\,0.5)\\,{$firstExp}\\,{$secondExp})))";
     }
 
     public static function EaseInCirc(string $time): string
@@ -134,7 +135,7 @@ public static function EaseInBack(string $time): string
         $c1 = 1.70158;
         $c3 = $c1 + 1;
 
-        return "{$c1}*pow(({$time})\\,3)-{$c3}*pow(({$time})\\,2)";
+        return "{$c3}*pow(({$time})\\,3)-{$c1}*pow(({$time})\\,2)";
     }
 
     public static function EaseOutBack(string $time): string
@@ -157,7 +158,7 @@ public static function EaseInElastic(string $time): string
     {
         $c4 = (2 * M_PI) / 3;
 
-        return "if(eq(({$time})\\,0)\\,0\\,if(eq(({$time})\\,1)\\,1\\,-pow(2\\,10*({$time})-10)*sin(({$time})*10-10.75)*{$c4}))";
+        return "if(eq(({$time})\\,0)\\,0\\,if(eq(({$time})\\,1)\\,1\\,-pow(2\\,10*({$time})-10)*sin((({$time})*10-10.75)*{$c4})))";
     }
 
     public static function EaseOutElastic(string $time): string
@@ -188,12 +189,12 @@ public static function EaseOutBounce(string $time): string
         $n1 = 7.5625;
         $d1 = 2.75;
         $firstExpr = "{$n1}*pow(({$time})\\,2)";
-        $secondTime = "(({$time})-1.5)";
-        $secondExpr = "{$n1}*({$secondTime}/{$d1})*({$secondTime})+0.75";
-        $thirdTime = "(({$time})-2.25)";
-        $thirdExpr = "{$n1}*({$thirdTime}/{$d1})*({$thirdTime})+0.9375";
-        $fourthTime = "(({$time})-2.65)";
-        $fourthExpr = "{$n1}*({$fourthTime}/{$d1})*({$fourthTime})+0.984375";
+        $secondTime = "(({$time})-1.5/{$d1})";
+        $secondExpr = "{$n1}*{$secondTime}*{$secondTime}+0.75";
+        $thirdTime = "(({$time})-2.25/{$d1})";
+        $thirdExpr = "{$n1}*{$thirdTime}*{$thirdTime}+0.9375";
+        $fourthTime = "(({$time})-2.65/{$d1})";
+        $fourthExpr = "{$n1}*{$fourthTime}*{$fourthTime}+0.984375";
 
         return "if(lt(({$time})\\, 1/{$d1})\\,{$firstExpr}\\,if(lt(({$time})\\,2/{$d1})\\,{$secondExpr}\\,if(lt(({$time})\\,2.5/{$d1})\\,{$thirdExpr}\\,{$fourthExpr})))";
     }
@@ -202,9 +203,9 @@ public static function EaseInOutBounce(string $time): string
     {
         $x1 = self::EaseOutBounce("1-2*({$time})");
         $x2 = self::EaseOutBounce("2*({$time})-1");
-        $gtExpr = "(1-({$x1}))/2";
-        $ltExpr = "(1+({$x2}))/2";
+        $ltExpr = "(1-({$x1}))/2";
+        $gtExpr = "(1+({$x2}))/2";
 
-        return "if(lt(({$time})\\,0.5)\\,{$ltExpr}\\,{$gtExpr}";
+        return "if(lt(({$time})\\,0.5)\\,{$ltExpr}\\,{$gtExpr})";
     }
 }