From 2232beacb7af14cf0f4575a9d05e1dcf315399c4 Mon Sep 17 00:00:00 2001
From: zefie <zefie@zefie.net>
Date: Sun, 26 Apr 2026 22:01:14 -0400
Subject: [PATCH] fix ALP generation and default to it

---
 zefie_wtvp_minisrv/app.js                     |  8 ++++-
 .../includes/classes/WTVImage.js              | 30 ++++++++++++++++---
 2 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/zefie_wtvp_minisrv/app.js b/zefie_wtvp_minisrv/app.js
index 94b69e38..832ff2ca 100644
--- a/zefie_wtvp_minisrv/app.js
+++ b/zefie_wtvp_minisrv/app.js
@@ -1314,9 +1314,15 @@ async function sendToClient(socket, headers_obj, data = null) {
     }
    
 
+    let imageArtemisType = 'ALP'
     // Add last modified if not a dynamic script
     if (socket_sessions[socket.id]) {
         if (socket_sessions[socket.id].request_headers) {
+            if (socket_sessions[socket.id].request_headers.query) {
+                    if (socket_sessions[socket.id].request_headers.query.forceALF) {
+                        imageArtemisType = 'ALF';
+                    }
+            }
             if (socket_sessions[socket.id].request_headers.service_file_path) {
                 // Don't change Last-modified header if provided already
                 if (!headers['Last-Modified'] && !headers['minisrv-no-last-modified']) {
@@ -1354,7 +1360,7 @@ async function sendToClient(socket, headers_obj, data = null) {
             if (minisrv_config.config.image_decoder.image_formats && minisrv_config.config.image_decoder.image_formats.includes(headers_obj[contype_key].toLowerCase())) {            
                 const convertOpts = {
                     jpegQuality: minisrv_config.config.image_decoder.jpg_quality,
-                    type: 'ALF'
+                    type: imageArtemisType
                 };
 
                 if (minisrv_config.config.image_decoder.max_height > 0) convertOpts.maxHeight = minisrv_config.config.image_decoder.max_height;
diff --git a/zefie_wtvp_minisrv/includes/classes/WTVImage.js b/zefie_wtvp_minisrv/includes/classes/WTVImage.js
index 502dd168..06c83e51 100644
--- a/zefie_wtvp_minisrv/includes/classes/WTVImage.js
+++ b/zefie_wtvp_minisrv/includes/classes/WTVImage.js
@@ -17,7 +17,6 @@
  *
  *   ALP – the alpha table is prefixed with a black (0,0,0) phantom entry so
  *          that palette index 0 is always fully-transparent black.
- *          ALP encoding does not yet work correctly.
  *   ALF – the alpha table is suffixed with a black (0,0,0) phantom entry
  *          (last palette slot is fully-transparent black).
  *
@@ -367,6 +366,25 @@ class WTVImage {
         return { data: Buffer.concat(chunks), endOffset: offset };
     }
 
+    /**
+     * Build the Artemis alpha lookup table payload for ALP/ALF.
+     *
+     * ALP stores its alpha table with a phantom transparent palette entry
+     * at index 0, so the payload omits that slot and encodes only the
+     * remaining indices.
+     * ALF stores its alpha table directly and may be left full-length.
+     */
+    buildArtemisAlphaTable(type, alphaTable) {
+        if (type !== 'ALP') return Buffer.from(alphaTable);
+
+        // Drop the phantom transparent index 0, then trim trailing opaque values
+        // since ALP app payloads are typically truncated like ALF.
+        const table = alphaTable.slice(1);
+        let trimEnd = table.length - 1;
+        while (trimEnd >= 0 && table[trimEnd] === 0xFF) trimEnd--;
+        return Buffer.from(table.slice(0, trimEnd + 1));
+    }
+
     // ---------------------------------------------------------------------------
     // Artemis alpha extension codec
     // ---------------------------------------------------------------------------
@@ -461,7 +479,11 @@ class WTVImage {
         const rgba = Buffer.from(origData);
         for (let i = 0; i < pixelCount; i++) {
             const idx = indices[i];
-            rgba[i * 4 + 3] = (idx < alphaTable.length) ? alphaTable[idx] : 0xFF;
+            if (type === 'ALP') {
+                rgba[i * 4 + 3] = (idx === 0) ? 0x00 : ((idx - 1 < alphaTable.length) ? alphaTable[idx - 1] : 0xFF);
+            } else {
+                rgba[i * 4 + 3] = (idx < alphaTable.length) ? alphaTable[idx] : 0xFF;
+            }
         }
 
         return { rgba, width, height, type };
@@ -697,7 +719,7 @@ class WTVImage {
             realPalette[transparentIdx * 3 + 2] = 0;
         }
 
-        const emitAlphaTable = fullAlpha;
+        const emitAlphaTable = this.buildArtemisAlphaTable(type, fullAlpha);
         const hasTransparent = bestZeroIdx >= 0;
 
         // Re-encode the LZW image stream from our (possibly swapped) indices.
@@ -917,7 +939,7 @@ class WTVImage {
 
         // Emit full alphaTable (no truncation; WebTV may default missing
         // entries to 0x00 transparent rather than 0xFF opaque).
-        const emitAlphaTable = finalAlpha;
+        const emitAlphaTable = this.buildArtemisAlphaTable(type, finalAlpha);
 
         const minCodeSize = Math.max(2, Math.ceil(Math.log2(colors)));
         const appExtBlock = this.buildAppExtension('Artemis ', type, emitAlphaTable);